Dr Ziyang Song

Prof. Dazhang Ling Miao

Laurent Ruhlmann

Dr Yaokang Lv

Dazhang Zhu

Liangchun Li

Lihua Gan

Mingxian Liu

Prof. Liangchun Zhu

Prof Li

Prof Mingxian Lihua Gan

Liu

Prof Laurent Ruhlmann

Keywords: self-assembly, carbon superstructure, ultrastable charge storage, proton-coupled redox kinetics, energy storage

Designing ingenious and stable carbon nanostructures is critical but still challenging for use in energy storage devices with superior electrochemistry kinetics, durable capacitive activity, and high rate survivability. To pursue the objective, a simple self-assembly strategy is developed to access carbon superstructures built of nanoparticle embedded plates. The carbon precursors, 2,4,6-trichloro-1,3,5-triazine and 2,6-diaminoanthraquinone can form porous organic polymer with "protic salt"-typed rigid skeleton linked by -NH2 + Cl --"rivets", which provides the cornerstone for hydrogen-bonding-guided self-assembly of the organic backbone to superstructures by π-π plane stacking. The ameliorative charge density distribution and decreased adsorption energy in as-fabricated carbon superstructures allow the high accessibility of the build-in protophilic sites and efficient ion diffusion with a low energy barrier. Such superstructures thus deliver ultra-stable charge storage and fast proton-coupled redox kinetics at the structural-chemical defects, contributing to unprecedented lifespan (1,000,000 cycles), high-rate capability (100 A g -1 ) for carbon-based supercapacitors, and an ultrahigh energy density (128 Wh kg -1 ) for Zn-ion hybrid supercapacitors. The self-assembled carbon superstructures significantly improve the all-round electrochemical performances, and hold great promise for efficient energy storage.

Introduction

With fascinating characteristics of abundance, high electrical conductivity, environmental benignity, and stable electrochemistry, carbon-based materials have been widely used as electrodes for energy storage devices such as supercapacitors and Zn-ion hybrid capacitors. [1] Electrical energy can be stored through reversible electrosorption of charged species at the carbon-electrolyte interface, enabling fast energy harvesting/delivering in seconds and theoretical work lifespan of more than a million cycles. [2] Crafting intrinsic heterogeneous electrochemically active sites within carbon framework can contribute additional pseudocapacitance, further boosting the energy storage performance. [3] Unfortunately, this scenario is always accompanied with sluggish electrochemistry kinetics and degenerated scaffold firmness caused by heteroatomic motifs, triggering dramatic activity loss and insufficient power/cycle durability. [4] As a result, it is difficult for the fabricated devices to achieve millions of cycles in theory. In fact, the presently reported service life of carbon-based devices is rarely more than 200,000 cycles, especially at large current rates.

The surface chemistry, although crucial, affects the charge transfer dynamics and functionality redox responses of carbon electrodes in a chemistry sensitive/influenced process only if that chemistry is accessible for the electrolyte ions. [5] Three-dimensional carbon superstructures constructed from the assembly of low-dimensional segments constitute attractive prospects for energy applications. [6] This is because the superstructures inherit the desirable features of their building blocks and gain certain extra unconventional advantages, such as exceptional skeleton robustness, more exposed electroactive sites, and fast ion transfer kinetics. [7] Therefore, it is essential to fundamentally design stable carbon superstructures to allow the high availability of heteroatomic motifs and efficient ion migration with lower energy hurdles, for comprehensively improving device performances to match the expected energy storage target.

The selection of small molecules with customized chemical structure, composition and selfassembly behavior as alternative precursors to design functionalized carbons is still an interesting and ongoing work to maximize their applications in energy storage. [7a, 8] The triazine unit, a strong electroactive building block, features with highly stable C=N covalent bonds and thus provides a high density of electroactive moieties. [9] Such structure bearing good electronic carrier ability and chemical stability harnesses unique charge-storage mechanism to enable high-kinetics, reversible-capacity, rapid-cycling devices. [10] Meanwhile, given the complementary electronic attributes, the electron-withdrawing benzoquinone unit can enable two reversible one-electron transfer reactions per carbonyl center. [11] This quinone/hydroquinone transformation brings rapid electron migration in the charge/discharge process, displaying robust redox reactivity and electrochemical reversibility to boost the energy/power delivery. [12] Therefore, such complementary molecular units combine both significant electrochemical stability and multi-electron heteroatomic chemical transfer process to fulfill efficient energy storage. In addition, quinone species containing C=O groups feature high pseudocapacitance activity, but generally suffer from unsatisfied cycle stability due to their dissolution from the electrode into the electrolyte. The conversion of monomer molecules into polymers (and carbons) can inhibit the dissolution, maintain the chemical stability and improve the cycle performance. [13] The problem left behind is how to bridge the gap between the precursors with electroactive carbonyl and triazine building blocks to stable and well-designed carbon superstructures to achieve the above goal.

Herein, a self-assembly strategy is demonstrated to design well-defined laminated organic polymers or carbon superstructures with jagged edges, based on the aromatic nucleophilic substitution reaction between 2,4,6-trichloro-1,3,5-triazine (TT) and 2,6-diaminoanthraquinone (DQ) through the grafting of -NH2 and -Cl (Figure 1a, e) followed by carbonization and activation processes using sodium cyanate as the activator. A mechanism investigation unravels the key role of -NH2 + Cl -bridges on the growth of porous polymer nanoparticles and H-bonding self-assembly of polymeric intermediates into the superstructures. Due to high thermal stability, the organic polymer superstructures can be readily converted into hierarchical porous carbons with maintained geometry by pyrolysis/activation. The advantages of the carbon superstructures are highlighted by the comprehensive performance improvements in carbonbased supercapacitors. Besides, a constructed Zn-ion hybrid supercapacitor, involving a carbon superstructure cathode, a zinc metal anode and an aqueous Zn(CF3SO3)2 electrolyte, also delivers remarkable energy storage performances. Systematic characterizations coupled with kinetics analysis identify the source of the exceptional charge storage as high-kinetics ion binding at the structural-chemical defects and the proton-coupled multielectron redox process of heteroatomic motifs in the ultrastable carbon superstructures.

Results and Discussion

Superstructure Formation Mechanism.

The synthetic route of the carbon superstructures was mainly involving three stages: i) Formation of polymer nanoparticles by aromatic nucleophilic substitution reaction of TT/DQ (Figure 1a, b); ii) Self-assembly of the nanoparticles into organic polymer superstructures (Figure 1c); iii) Pyrolysis/activation conversion to carbon superstructures (Figure 1d). Due to the electron-pulling effect of the halogen bonds, and the electron-pushing ability of the amine groups, TT can couple with DQ very quickly (~1 min) to yield polymer nanoparticles (~70 nm) possessing hexameric "protic salt"-like conjugated skeleton bridged by -NH2 + Cl -groups (Figure 1e, Figure S1). The quaternary ammonium salt linkers serve as the "rivets" to significantly enhance the rigidity of the polymer scaffold, which is crucial for the following self-assembly process. There are hydrogen-bonding interactions among -NH2 + Cl -linkers and carbonyl groups within the adjacent network chains in the form of N-H…O and N-H…N (Figure 1f, Figure S1). This interaction promotes the π-π plane stacking of the rigid conjugated building blocks, benefiting directed chain-like self-assembly to layered superstructures with zigzag-like edges (Figure S2). X-ray powder diffraction patterns (XRD) unravel the evolution of structural regularity of self-assembled TT-DQ polymer networks (Figure 1g). Such a selfassembly behavior lasts about 3 h to get stable and porous superstructures with relatively concentrated pore sizes of ~3.2 nm (Figure 1h, i). Finally, the porous polymers can be converted into hierarchical porous carbons with inherited superstructures via common carbonization/activation, due to the high thermal stability (Figure 1j-n). It is inferred that rigid -NH2 + Cl -bridges are the footstone for the self-assembly of polymeric intermediates to the superstructures. To prove this, triethylamine (TEA) was added to the reaction system to remove HCl from -NH2 + Cl -linkers of TT-DQ (Figure 2a), which would result in the formation of -NH-linkers (Figure 2b) between TT and DQ. XPS spectra also reveals the absence of Cl element in the resultant organic polymer (Figure 2c). High flexible -NH-linkers cause the intertwist of the polymer chains and thus lead to the deformation of TT-DQ framework. XRD patterns (Figure 2d) indicate much less regular skeleton structure of TT-DQ compared with those shown in Figure 1f. As a result, the lack of rigid -NH2 + Cl --linkers is unfavorable for the plane π-π stacking to get regular superstructures.

The as-synthesized flexible TT-DQ polymer with -NH-linkers exhibits disordered morphologies at the polymerization times of 1 and 180 min (Figure 2e-f), and inferior pore structure (Table S1).

Physicochemical Characterization of Carbon Superstructures.

In addition to topology, the pore structure and surface chemistry of the carbon superstructures derived from different polymerization times were further studied. The nitrogen sorption isotherms with a rapid adsorption at low relative pressure and a hysteresis loop at middlepressure region (Figure 3a) reveal the micro-, and mesoporous texture (Figure 3b). [14] The carbon superstructures exhibit ultrahigh surface areas (up to 1993 m 2 g -1 , Table S2) and hierarchical pore structure, which offer ample adsorption sites and highly open channels and thus are expected to enhance the electrolyte transport kinetics and charge storage capability. [15] In the carbon superstructures, N and O species are homogeneously distributed in the skeleton (Figure S3). X-ray photoemission spectroscopy (XPS, Figure 3c) identifies high contents of N (6.49-10.22 wt.%) and O (5.04-7.81 wt.%) elements (Table S2). The N 1s signal of the carbon superstructures (obtained by polymerization of 180 min follow by carbonization/activation) are fitted by three peaks (Figure 3d) assigned to the pyridinic nitrogen at 398.2 eV (N-6, 37.4%), the pyrrolic nitrogen at 400.3 eV (N-5, 34.5%), and the quaternary nitrogen at 401.8 eV (N-Q, 28.1%). [16] Three typical peaks at 531.6, 531.92, and 533.64 eV are observed in O 1s spectra (Figure 3d), corresponding to O-1 (C=O, 69.1%) and O-2 (C-OH/C-O-C, 30.9%) groups. [17]

Electrochemical Energy Storage Kinetics.

The electrochemical performances of the carbon superstructures for H + -hosting supercapacitors were investigated. Highly symmetric galvanostatic charge/discharge (GCD) profiles (Figure 4a, Figure S4) reveal superior electrochemical reversibility and charge storage behaviors of the carbon devices. [18] Benefiting from the well balance between geometry merit, pore structure parameters and functionality (Table S2), the optimal carbon superstructures originated from the polymerization time of 180 min delivers the highest electrode capacitance of 468 F g -1 at 1 A g -1 . We calculated the respective capacitance contribution from electrical double layer capacitances (CE) and pseudocapacitance (CP). [19] From GCD data (1-100 A g -1 ), the CE value is 314 F g -1 , and the CP contribution is 154 F g -1 , accounting for 32.9% of the total electrode capacitance (Figure S5a), which proves high redox activity of the retained heteroatom functionalities after carbonization. A remarkable capacitance of 269 F g -1 is still maintained at 100 A g -1 , demonstrating a superior large-current tolerance. Attracted by high capacitance and rate capability, the detailed capacitive storage behaviors of the assembled supercapacitors were studied by cyclic voltammetry (CV) curves based on the Dunn method (see Supporting Information Section S4 for details). [20] Quasi-rectangular shapes with two redox couples are observed (Figure 4b), which are linked to the ion-adsorption behavior and heteroatomic redox reactions of nitrogen species and carbonyl groups. [21] Two pairs of redox peaks at 0.37/0.32 and 0.49/0.44 V are attributable to the quinone/hydroquinone switching and pyridinic/pyrrolic nitrogen response. [21,22] Upon increasing the scan rate from 10 to 500 mV s -1 , CV profiles remain rectangular, with only slight shifted redox peaks, substantiating the accelerated ion/electron transfer dynamics and boosted redox reaction reversibility even at large scan rates. [23] The current density (i) and the scan rate (v) of a supercapacitor follow the relationship of i = kv b , where the power-law exponent of b is a vital index to estimate the charge-storage dynamics. Generally, the b value of 0.5 corresponds to sluggish reaction kinetics, while b = 1 signifies an ideal supercapacitor with ultrarapid reaction kinetics. [24] By plotting the log i against the log v, the b-values can be determined to be 0.98-0.99 for typical oxidation (O)/reduction (R) peaks in the scan-rate range of 10-500 mV s -1 (Figure 4c), corroborating the ultra-fast charge-storage kinetics of the carbon-based device. Almost 99.7% of the total stored charge is achieved by fast-kinetics process at 500 mV s -1 (Figure S6), which include the electric doublelayer capacitance and the most surface faradic pseudocapacitance, [5c, 20a] confirming that the energy can be easily stored and delivered. The capacitive contribution from the fast-kinetics processes distinctly dominates that of the slow-kinetics processes at all scanning rates (Figure 4d). The slow electrode capacitance gradually decays with the increase of scan rates due to charge-transfer limited or diffusion-controlled inner Faraday reactions, [25] while rapidcapacitance remains unchanged (367 F g -1 ).

Even at higher mass loadings (25 and 50 mg cm -2 ), as-fabricated supercapacitors still deliver very low ion diffusion resistances of 0.20-0.23 Ω (Figure S7), small relaxation time constants of 0.47-0.83 s (Figure 4e), and ultrafast electrochemical capacitance storage (Figure S8 and Table S3). Moreover, the assembled supercapacitors exhibit high capacitive storage of 350-418 F g -1 at 1 A g -1 , remarkable survivability at 100 A g -1 (Figure 4f, Table S4) and cycle stability (Figure S9) even at ultrahigh active substance loadings, highlighting the ultrarapid ion/charge migration kinetics. The outstanding supercapacitive activity profit from the well-orchestrated carbon superstructures, which acts as stable interconnected conductive networks during the high-rate charge/discharge process to boost the electron conduction along the layered skeleton topography and push ion permeation inside the electroactive voids. Besides, the assembled supercapacitor with the active substance loading of 10 mg cm -2 displays a notable increment of initial capacitance running up to 60,000 cycles, which can be assigned to the greatly enhanced accessibility of redox-active centers by electrolyte protons. More encouragingly, the device holds 93.1% capacitance retention and a coulombic efficiency approaching to 100% when the serve term is extended to 1,000,000 cycles (Figure 4g). Post mortem characterizations of the carbon superstructures after cycling by SEM, EIS, and XPS spectra suggests the excellent stability of the carbon superstructures (inset of Figure 4g, Figure S10). To the best of our knowledge, the ultralong-term work lifespan reported here are unprecedented for carbon-based supercapacitors (Table S5). The boosted carbon/ion interface compatibility further extend the highly electroactive carbon superstructures to different types of electrolytes (Figure S11, 12) for building high energy supercapacitors (up to 113.8 Wh kg -1 ). Notably, the overall performances of the assembled carbon-based supercapacitors substantially outclass those of recently reported devices, not only referring to the durable capacitive activity, but also concerning the high-rate cyclability (Table S5).

Heteroatomic Transformation Mechanism.

The fabricated carbon-based supercapacitors demonstrate excellent supercapacitive activity and durability, due to unique structural and functional design (Figure 4h). To better comprehend the relationship between the electrochemical functionality and the charge storage mechanisms of carbon superstructures, we further performed ex situ XPS tests at multiple discharging/charging states based on a typical GCD curve (Figure 5a) to capture more chemical transformation details of heteroatomic motifs. N-6 and O-1 species gradually decrease in the process of 1-0 V discharging and nearly return back to the original value during 0-1 V charging, while N-5 resonance peak undergoes a reverse variation trend (Figure 5b,c). In contrast, N-Q without electrochemical activity is basically unchanged. These results verify that reversible switching reactions of N-6, N-5 and O-1 take place via the chemical interactions with H + during the full discharging/charging processes. Ex situ potential-dependent EIS of the carbon-based supercapacitors was also monitored to analyze ion diffusion resistivity and electron transport dynamics during the heteroatomic chemical transformation process, as shown in Figure 5d,e.

Very low ion transport resistances (Rs=0.18-0.31 Ω, Table S6) during the cycling confirm the fast charge-transfer kinetics. During discharging, Rs and Rct are on a voltage-driven downward trend. H + diffusion resistivity (σ) and transmission coefficient (DH + ) can be calculated based on the equations given in Supporting Information Section S5. There is a lessening trend in σ from 0.96 to 0.64 Ω s -0.5 , accompanying with the enlargement of DH + from 1.23×10 -8 to 2.77×10 -8 cm 2 s -1 (Figure 5f, Table S6). The values of Rs/Rct and σ/DH + get back during the charging process (Figure 5e,g). This result demonstrates reversible ion-kinetics transformation behaviors within the functionalized superstructure host, and low operation potentials promote H + diffusion to the electrode/electrolyte interface for the transformation of electroactive N/O species. Besides, Bader charge analysis was performed to unravel the chemical interaction between electrolyte ion and introduced active sites within the carbon matrix. Negative net charges of H (-0.49 eV corresponding to N-6 and -0.50 eV to N-5) indicate that the electron of H tends to be delocalized (lost). They thus tend to flow toward N-6/N-5 (+1.19 and +1.09 eV) to form stable configurations, embodying the strong chemical interaction between electroactive nitrogen sites and H + ions (Figure 5h). [26] Particularly, N-6/N-5 species bearing a lone electron pair for conjugation with the π-conjugated rings drive the interconversion between =N-and -NH-during the charge/discharge process. [27] There are also significant charge shifts from H (-0.14 eV) to electron-withdrawing quinone-type O-1 (+0.91 eV), being beneficial to yield surface adsorption-induced pseudocapacitive response. This process triggers the availability of more H + around N-6, N-5 and O-1 active centers and drives the proton-coupled reversible redox switch, bringing enhanced electrochemical energy storage. [28] The first-principles simulation based on the density functional theory (DFT) method was performed to further elucidate the above experimental results. The adsorption ability of H ion is remarkably strengthened to achieve a relative adsorption energy (∆Ea) of -4.69 and -4.85 eV for N-6 and N-5 sites (Figure 5i). This result infers that both active species are more energyfavorable for H + chemisorption to trigger pseudocapacitive reactions and modulate the electronic structure for facilitating the electron transfer within the carbon matrix. [29] The capture ability of O-1 to H atoms is boosted to deliver a binding energy of -4.38 eV (Figure 5i), indicating the robust electrochemically reactivity of carbonyl group. [30] In addition, top (Figure 5j) and side (Figure S13) views of the electron density difference were demonstrated by subtracting the charge densities of H and C atoms from N-6, N-5 and O-1 to understand the bonding nature of the adsorbed H atoms in depth. The charge depletion of H and much charge accumulation around N/O active regions are explicitly observed. A net gain of charge in these heteroatom species suggests the charge transfer tendency from the adsorbed H to the nearest C atoms, which signifies that N/O significantly boost the affinity between electrolyte ions and heteroatom-substituted carbons. [31] This finding illuminates that heteroatomic motifs throughout the carbon superstructures can effectively lower the energy barrier of chemical interactions between electroactive sites and protons, boosting the proton-driven charge storage process. Besides, the minimum diffusion energy paths of H ions in different models are

Proton-Assisted Zn-Ion Storage in Carbon Superstructures.

We further constructed a Zn-ion hybrid supercapacitor by employing zinc metal as the anode and carbon superstructures as the cathode in aqueous Zn(CF3SO3)2 electrolyte. The Zn-ion device synergizes the energy storage mechanisms of supercapacitors with rapid ion adsorption/desorption processes and batteries with faradaic reversible reactions, [32] which are expected to achieving high energy-power delivery and long-life performance. Three identical assembled Zn-ion devices exhibit the same GCD charge/discharge behavior (Figure S16 and Figure 17). The fabricated device exhibits a high capacity of 198 mA h g -1 at 0.5 A g -1 , together with a reversible capacity of 120 mA h g -1 at 50 A g -1 . Besides, the voltage drop reflected by GCD curves is only 0.09 V at a high current density level of 50 A g -1 , evidencing that the introduction of heteroaromatic species is capable of significantly enhancing electrical conductivity and promoting ion/electron transport dynamics. [33] Moreover, the device capacity is switched back to 196 mA h g -1 after 70 successive cycles at various current rates (Figure S17). To describe the degree of capacitive effect of the device, the surface-driven capacitive and diffusion-controlled energy storage processes were investigated (Figure S18), which suggest the rapid-capacitive dominated charge storage with a certain degree of diffusioncontrolled redox reactions. [34] More encouragingly, the aqueous Zn//carbon device achieves an ultrahigh energy density of 128 Wh kg -1 at 327 W kg -1 (based on the mass of carbon cathode), outperforming most previously reported Zn-based hybrid devices (Figure 6a). [1f, 2a, 4a, 32, 35] A high power density of 29.7 kW kg -1 with a corresponding energy density of 70.6 Wh kg -1 can be obtained at 50 A g -1 , showing high energy/power delivery. Presently, many reported Zn-ion devices with high energy densities are generally estimated without considering the mass of Znanode. Based on the total weight of zinc anode and carbon cathode, the fabricated Zn-ion device shows an energy density of 20.9 Wh kg -1 , 1.3 times of most recently reported value (16.2 Wh kg -1 ). [35d] Besides, the device shows a prolonged cycling performance with 91.8% capacity retention and 99.6% coulombic efficiency over 200,000 cycles at 40 A g -1 (Figure 6b). SEM images of the carbon cathode after cycling (Figure S19) indicate the superb strutural stability of the carbon superstructures in the hybrid supercapacitor. Zn 2+ cations are widely recognized as efficient active ions stored in carbon cathode, [2a, 36] but it is still unknown whether protons are active during Zn-ion storage. In view of the mildly acidic environment of Zn(CF3SO3)2 electrolyte (pH=4.12) and the smaller size of hydrated protons, [3a] investigation of the role of H + is essential to better understand the Zn-ion storage mechanism.

Therefore, we performed comparative electrochemical experiments and a series of ex-situ characterizations. An aqueous HCF3SO3 solution with the same pH of Zn(CF3SO3)2 was employed as the electrolyte to explore the possible participation of H + during Zn 2+ storage (Figure S20a). HCF3SO3-based device presents a capacity of 40 mAh g -1 , which suggest that hydrogen ions take part in the cathodic electrochemical reaction of the device. With the increase of the concentration of H + (pH value from 6.32 to 1.02), the device capacities significantly boost from 6 to 94 mAh g -1 (Figure S20b,c). This result further indicates that protons take part in the electrochemical reaction of the carbon cathode. Besides, ex-situ high-resolution O 1s XPS spectra was performed to track the surface variations of the carbon cathode at the discharging state of 0 V in hybrid Zn-ion device using HCF3SO3 electrolytes with different pH values (1.02-6.32). The contents of carbonyl groups reduce gradually with the decrease of pH values (Figure S20d), which indicates that more carbonyl functional groups are chemically consumed by more H + , supporting the redox process between C=O and H + in Equation (3) of Figure 6f.

Ex situ XPS measurement at different voltages (Figure 6c) was performed to track the surface variations of the carbon cathode. Electrochemical hydrogen adsorption/desorption leads to a dynamic local alkaline environment (Figure 6f, Equation (1)), [1f] in which OH -anions strongly coordinate with Zn 2+ to form Zn(CF3SO3)2[Zn(OH)2]3•xH2O product (confirmed by XRD analysis, Figure S21). [2c] While the generated H + cations (Figure 6f, Equation ( 2)) diffuse into carbon cathode to account for the reversible redox reactions of oxygen species. [37] During the discharging from 1.8 to 0.9 V, C=O groups in carbon cathode is continuously reduced to C-OH (Figure 6d) by gaining protons and electrons (Equation ( 3)). Meanwhile, H + and Zn 2+ ions are transferred to carbon cathode at the solid-liquid interface, named as C-Zn(H). With the proceeding of the discharging to 0 V, the C-Zn(H) further undergoes a metathesis of Zn 2+ and H + with more activated C=O groups, where the protons transferred from water are released back into the electrolyte, finally yielding C-O-Zn configuration [38] (Figure 6e, f, Equation (4), Fig. S22). During the charging, the reversibility of this process is followed. The chemical variations of O species could be a positive proof of the co-uptake of H + and Zn 2+ . The overall proton-assisted Zn-ion charge-storage mechanism within ultrahigh-rate superstructure host is depicted in Figure 6g, involving reversible electrochemical hydrogen adsorption/desorption and conversion in oxidation states of oxygen species during each round-trip charge-discharge cycle. Element mapping images (Figure S23) also reveal the highly reversible formation/dissolution transition of Zn(CF3SO3)2[Zn(OH)2]3•xH2O, supporting the adsorption/release behaviors of protons at the discharge/charge process (Table S7). The Zn-ion hybrid device configuration and overall reaction mechanism are depicted in Figure 6f. Three different electronic devices, 1.5 V light-emitting-diode (LED) lamp, 3 V miniature fan and 5 V mobile phone, were successfully powered by connecting the constructed Zn-ion hybrid supercapacitors in series (Figure 6h). Besides, two Zn-ion devices in series can successfully drive an electronic laser presenter (3 V working voltage) to present 26-page slides constantly for more than 60 min (Figure 6i), due to the good energy storage capability of the device.

For both the supercapacitor and Zn-ion hybrid device applications, the structural and functional design of carbon superstructures contribute to the all-round performance improvements in terms of supercapacitive activity and durability. Firstly, robust carbon superstructures with excellent mechanical strength can prevent skeleton deformation under large-current cycling rates and minimize the ion/electron transport obstruction within the whole carbon scaffold, forcing the achievement of ultrarapid reaction kinetics and ultrastable longevity. Secondly, large surface area and multi-scale porosity of carbon scaffold afford ample ion-interaction platforms for promoting chemical adsorption process, and allow the high accessibility of the build-in protophilic sites and efficient ion transport with low energy barriers.

Thirdly, rich heteroatomic motifs dispersed throughout the carbon superstructures afford dense redox-active sites bonded to electrolyte cations, which trigger proton-driven high-rate redox kinetics to supplement remarkable pseudocapacitance storage/delivery. Their synergism optimizes the supercapacitive performances and further elevating the energy/power supplies of carbon superstructures to superior levels.

Conclusion

In conclusion, a self-assembly strategy is demonstrated to design carbon superstructures derived from TT-DQ. Structural evolution investigation untangles the key roles of -NH2 + Cl -bridges and hydrogen-bonding interaction on the self-assembly process of polymeric intermediates into rigid polymer superstructures and carbon derivatives. With prominent merits in superstructures, the fabricated carbon-based supercapacitor features excellent electrochemical performance in terms of ultrahigh rate performance (269 F g -1 at 100 A g -1 ) and long-life cyclability (93.1% capacitive activity after 1,000,000 cycles at 100 A g -1 ).

Significantly, an aqueous Zn-ion hydrid supercapcitor delivers an ultrahigh energy density of 128 Wh kg -1 and an ultralong duration of 91.8% retention over 200,000 cycles at 40 A g -1 .

Marriage of comprehensive characterizations and dynamic analysis illustrate that functionalized carbon superstructures can effectively lower the ion-binding energy barriers at the structural-chemical defects, promoting proton-coupled charge storage on the electrode surface. This work offers a new insight in the improvement of charge storage performance through design of structure engineering and surface chemistry.

Keywords: self-assembly, carbon superstructure, ultrastable charge storage, proton-coupled redox kinetics, energy storage.

Ziyang Song, Ling Miao, Laurent Ruhlmann, Yaokang Lv, Dazhang Zhu, Liangchun Li, Lihua Gan, and Mingxian Liu*

Self-Assembled Carbon Superstructures Achieving Ultra-Stable and Fast Proton-Coupled Charge Storage Kinetics

The table of contents entry

Complementary acceptor-donor molecules of 2,4,6-trichloro-1,3,5-triazine and 2,6diaminoanthraquinone form porous organic polymer with "protic salt"-typed rigid skeleton linked by -NH2 + Cl --"rivets", which offers the cornerstone for H-bonding self-assembly of the organic backbone to carbon superstructures by π-π plane stacking. The superstructures achieve ultra-stable and fast proton-coupled charge storage kinetics, giving unprecedented lifespan (1,000,000 cycles) and high energy-density for carbon (zinc) supercapacitors. S3. The capacitances fitted by the area of CV profiles at different scan rates, the rate performances, the range of b values, and the capacitance originated from fast-kinetic process of the carbon electrode with different mass loadings of active materials in H2SO4 electrolyte. Table S4. Supercapacitive performances of the carbon electrode at different current densities under various mass loadings of active materials in H2SO4 electrolyte. Table S5. Comparison of Cs, mass loading of active materials and cycle stability of reported carbon electrodes for supercapacitors in the recent literatures.

Section S5. Kinetics Exploration of Carbon-Based Supercapacitors. S7. X-ray electron diffraction spectroscopy data of carbon cathode corresponding to various stages of the discharging/charging courses shown in Figure S23.

working electrodes with a Celgard 3501 polypropylene membrane in the middle using 100 μL different electrolytes of 6 M KOH, 1 M H2SO4, 1 M Na2SO4, LiTOF (lithium trifluoromethane sulfonate in deionized water, 21 mol kg -1 ), 1 M TEMABF4/ACN (triethylmethylammonium tetrafluoroborate in deuterated acetonitrile), neat EMIMBF4 (1-ethyl-3-methylimidazolium tetrafluoroborate).

The performances were characterized on a CHI660E electrochemical workstation including cyclic voltammetry (CV), galvanostatic charge-discharge (GCD), and electrochemical impedance spectroscopy (EIS). The gravimetric capacitance (Cs) of a single electrode of the linear supercapacitors were calculated based on the following equations:

Cs (F g -1 ) = 4 × I × ∆t m × ∆V (1)
For a nonlinear supercapacitor, the capacitance is calculated from the integrated form:

C = ∫ dQ ∫ dV = ∫ Idt ∫ dV = i∆t ∆V (2)
The energy density (E) and power density (P) of the supercapacitors were calculated according to the following equations:

E (Wh kg -1 ) = 1 7.2 × 4
Cs∆V 2

(3)

P (W kg -1 ) = E ∆t × 3600 (4)
I (A), ∆t (s), m (g), and ∆V (V) denotes charge current, discharge time, the total mass of active materials on two electrodes, and the voltage window, respectively.

Zn-Ion Hybrid Supercapacitor. Carbon//Zn(CF3SO3)2//Zn hybrid supercapacitor was assembled in 2032 coin-type cell with the as-prepared carbon electrode as cathode, Zn foil as anode and 3 M Zn(CF3SO3)2 as electrolyte. The specific capacity (Cm, mAh g -1 ) and cycling performance were estimated on a LAND-CT3001A multichannel galvanostat within the voltage range of 0-1.8 V, CV and EIS tests were performed using a CHI660E electrochemical workstation.

Section S3. Physicochemical Analysis of the Carbon Superstructures.

C = k1 + k2v -1/2 (7)
where the capacitance C includes a rate-independent component k1 (generally related to CE) and a diffusion-limited part determined by the scan rate, v = T -1 . In the GCD test, T is the discharge time. CE can be obtained from the intersection of fitting line and vertical axis. From GCD test, the CE values is 314 F g -1 , thus the CP contribution is 154 F g -1 (32.9% of the total electrode capacitance). the knee frequency (f) describes the maximum frequency at the phase angle of -45 o where the capacitive behavior is dominant. The higher f is, the faster the supercapacitor energy can be stored and released. The corresponding knee frequency is calculated to 6.67, 2.13, and 1.20 Hz.

The results reveal the good kinetics and high-rate capability of the electrode in acidic electrolyte.

Generally, the charge storage capability of the carbon superstructure device decreases with increasing mass loadings owing to that the elongated ion/electron transport routes under higher mass loadings lead to relatively sluggish electrochemically reaction kinetics and blocked supercapacitive activity. Rs and Rct slightly change even at 50 mg cm -2 , suggesting robust electrolyte reaction kinetics. Table S5. Comparison of Cs, mass loading of active materials and cycle stability of reported carbon electrodes for supercapacitors in the recent literatures.

Materials Cs F g -1 @A g -1

Mass Loading (mg cm -2 ) Lifespan %@Cycle@mV s -1 or A g -1 Ref.

MXene/graphene 383@1 N/A 97@30,000@200 mV s -1 S5 294@10 Hollow spheres 251@0.5 N/A 140@8,000@3 A g -1 S6 191@15 Doped carbons 348@0.5 2.5 92@35,000@20 A g -1 S7 123@80 Ordered carbon 236@0.5 1.0 105@10,000@50 mV s -1 S8 171@100 COF/aerogel 269@0.5 1.0 96@5,000@8 A g -1 S9 222@10 Porous carbon 231@0.1 1.8~2.7 123@80,000@10 A g -1 S10 150@10 Carbon nanofiber 279@0.5 N/A 122@10,000@5 A g -1 S11 165@20 Porous carbon 357@1 1.0~4.0 98@60,000@10 A g -1 S12 110@80 Carbon microspheres 301@0.2 8.0 100@5,000@5 A g -1 S13 210@5 Carbon fiber textile 220@0.5 N/A 100@10,000@5 mV s -1 S14 80@50 Carbon aerogels 300@0.5 1.5 92@5,000@2 A g -1 S15 221@10 Porous carbon 202@0.5 9.0~11.0 100@8,000@5 A g -1 S16 141@40 Carbon nanosheets 280@0.5 N/A 103@10,000@6 A g -1 S17 228@100 Biomass carbon 307@0.5 N/A 96.5@10,000@5 A g -1 S18 181@30 Carbon sheets 208@0.2 106@100 N/A 99@20,000@1 V s -1 S19

Carbon

Superstructures 468@1 269@100 10.0 103.7@60,000@100 A g -1 93.1@1,000,000@100 A g -1 This Work

Figure 1 .

 1 Figure 1. (a) Schematic molecular structures of TT and DQ. (b) Formation of TT-DQ polymer

Figure 2 .

 2 Figure 2. (a) Schematic skeleton structure, (b) FT-IR spectrum, (c) wide-scan XPS spectra,(d)

Figure 3 .

 3 Figure 3. (a) N2 sorption isotherms, (b) pore size distributions, and (c) XPS survey spectra of

Figure 4 .

 4 Figure 4. Electrochemistry characterizations of the assembled optimal carbon-based supercapacitors in 1 mol L -1 H2SO4 electrolyte. (a) GCD curves, (b) CV profiles, (c) the fitting

Figure 5 .

 5 Figure 5. Heteroatomic chemical transition in the proton storage process. (a) A GCD profile.

  FigureS15), expediting the migration of electrolyte ions on electrochemically active sites.

Figure 6 .

 6 Figure 6. Electrochemical performances of the assembled Zn-ion device. (a) Ragone plots. (b)Stability after 200,000 cycles. (c) A typical GCD curve at 2 A g -1 and corresponding ex situ(d)

Figure S12 .

 S12 Figure S12. Comparison of electrochemical properties in different electrolytes. (a) Ragone plots and (b) radar chart of the five figure-of-merit for carbon-based devices. TableS3. The capacitances fitted by the area of CV profiles at different scan rates, the rate performances, the range of b values, and the capacitance originated from fast-kinetic process of the carbon electrode with different mass loadings of active materials in H2SO4 electrolyte. TableS4. Supercapacitive performances of the carbon electrode at different current densities under various mass loadings of active materials in H2SO4 electrolyte. TableS5. Comparison of Cs, mass loading of active materials and cycle stability of reported carbon electrodes for supercapacitors in the recent literatures.

Figure S15 .

 S15 Top view of H ion diffusion in N-5 doping structure (path 1) and the corresponding diffusion barrier energies at various states.Section S6. Electrochemistry Characterization of the Assembled Zn-IonDevice.

Figure S16 .

 S16 Figure S16. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a) GCD curves at 0.5 A g -1 ,(b) the capacity and energy density of the device 2 calculated by the integral area of the GCD curve at 0.5 A g -1 , and (c) comparison of electrochemical performance of three devices. Figure S17. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a, c, e) GCD curves and (b, d, f) rate performances. Figure S18. Investigation of the capacitive effect and diffusion-controlled energy storage behaviors of the device 2: (a) CV curves. (b) The fitting plots between logi and logv at the anodic peaks (bO) and the cathodic peaks (bR). (c) Normalized capacity contribution at different scan rates. Figure S19. SEM images of the carbon cathode in Zn-ion hybrid device (a) before and (b) after 200000 cycles. Figure S20. (a) pH values of 3 M Zn(CF3SO3)2 and HCF3SO3, (b) GCD curve at 0.5 A g -1 , and (c) relastionship between capacities of the carbon-based Zn-ion device and the pH values of HCF3SO3 electrolytes. (d) Ex situ high-resolution O 1s XPS spectra of the carbon cathodes using HCF3SO3 electrolytes with different pH values at the discharging state of 0 V.Figure S21. Ex-situ XPS spectra of Zn 2p.Figure S22. XRD patterns of carbon superstructure cathode at different charge/discharge states.Figure S23. Elemental mapping images of carbon cathode at five representative discharging/charging moments (A, B, C, D, and E). Table S7. X-ray electron diffraction spectroscopy data of carbon cathode corresponding to various stages of the discharging/charging courses shown in Figure S23.

Figure S18 .

 S18 Figure S16. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a) GCD curves at 0.5 A g -1 ,(b) the capacity and energy density of the device 2 calculated by the integral area of the GCD curve at 0.5 A g -1 , and (c) comparison of electrochemical performance of three devices. Figure S17. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a, c, e) GCD curves and (b, d, f) rate performances. Figure S18. Investigation of the capacitive effect and diffusion-controlled energy storage behaviors of the device 2: (a) CV curves. (b) The fitting plots between logi and logv at the anodic peaks (bO) and the cathodic peaks (bR). (c) Normalized capacity contribution at different scan rates. Figure S19. SEM images of the carbon cathode in Zn-ion hybrid device (a) before and (b) after 200000 cycles. Figure S20. (a) pH values of 3 M Zn(CF3SO3)2 and HCF3SO3, (b) GCD curve at 0.5 A g -1 , and (c) relastionship between capacities of the carbon-based Zn-ion device and the pH values of HCF3SO3 electrolytes. (d) Ex situ high-resolution O 1s XPS spectra of the carbon cathodes using HCF3SO3 electrolytes with different pH values at the discharging state of 0 V.Figure S21. Ex-situ XPS spectra of Zn 2p.Figure S22. XRD patterns of carbon superstructure cathode at different charge/discharge states.Figure S23. Elemental mapping images of carbon cathode at five representative discharging/charging moments (A, B, C, D, and E). Table S7. X-ray electron diffraction spectroscopy data of carbon cathode corresponding to various stages of the discharging/charging courses shown in Figure S23.

Figure S19 .

 S19 Figure S16. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a) GCD curves at 0.5 A g -1 ,(b) the capacity and energy density of the device 2 calculated by the integral area of the GCD curve at 0.5 A g -1 , and (c) comparison of electrochemical performance of three devices. Figure S17. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a, c, e) GCD curves and (b, d, f) rate performances. Figure S18. Investigation of the capacitive effect and diffusion-controlled energy storage behaviors of the device 2: (a) CV curves. (b) The fitting plots between logi and logv at the anodic peaks (bO) and the cathodic peaks (bR). (c) Normalized capacity contribution at different scan rates. Figure S19. SEM images of the carbon cathode in Zn-ion hybrid device (a) before and (b) after 200000 cycles. Figure S20. (a) pH values of 3 M Zn(CF3SO3)2 and HCF3SO3, (b) GCD curve at 0.5 A g -1 , and (c) relastionship between capacities of the carbon-based Zn-ion device and the pH values of HCF3SO3 electrolytes. (d) Ex situ high-resolution O 1s XPS spectra of the carbon cathodes using HCF3SO3 electrolytes with different pH values at the discharging state of 0 V.Figure S21. Ex-situ XPS spectra of Zn 2p.Figure S22. XRD patterns of carbon superstructure cathode at different charge/discharge states.Figure S23. Elemental mapping images of carbon cathode at five representative discharging/charging moments (A, B, C, D, and E). Table S7. X-ray electron diffraction spectroscopy data of carbon cathode corresponding to various stages of the discharging/charging courses shown in Figure S23.

Figure S21 .

 S21 Figure S16. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a) GCD curves at 0.5 A g -1 ,(b) the capacity and energy density of the device 2 calculated by the integral area of the GCD curve at 0.5 A g -1 , and (c) comparison of electrochemical performance of three devices. Figure S17. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a, c, e) GCD curves and (b, d, f) rate performances. Figure S18. Investigation of the capacitive effect and diffusion-controlled energy storage behaviors of the device 2: (a) CV curves. (b) The fitting plots between logi and logv at the anodic peaks (bO) and the cathodic peaks (bR). (c) Normalized capacity contribution at different scan rates. Figure S19. SEM images of the carbon cathode in Zn-ion hybrid device (a) before and (b) after 200000 cycles. Figure S20. (a) pH values of 3 M Zn(CF3SO3)2 and HCF3SO3, (b) GCD curve at 0.5 A g -1 , and (c) relastionship between capacities of the carbon-based Zn-ion device and the pH values of HCF3SO3 electrolytes. (d) Ex situ high-resolution O 1s XPS spectra of the carbon cathodes using HCF3SO3 electrolytes with different pH values at the discharging state of 0 V.Figure S21. Ex-situ XPS spectra of Zn 2p.Figure S22. XRD patterns of carbon superstructure cathode at different charge/discharge states.Figure S23. Elemental mapping images of carbon cathode at five representative discharging/charging moments (A, B, C, D, and E). Table S7. X-ray electron diffraction spectroscopy data of carbon cathode corresponding to various stages of the discharging/charging courses shown in Figure S23.

Figure S22 .

 S22 Figure S16. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a) GCD curves at 0.5 A g -1 ,(b) the capacity and energy density of the device 2 calculated by the integral area of the GCD curve at 0.5 A g -1 , and (c) comparison of electrochemical performance of three devices. Figure S17. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a, c, e) GCD curves and (b, d, f) rate performances. Figure S18. Investigation of the capacitive effect and diffusion-controlled energy storage behaviors of the device 2: (a) CV curves. (b) The fitting plots between logi and logv at the anodic peaks (bO) and the cathodic peaks (bR). (c) Normalized capacity contribution at different scan rates. Figure S19. SEM images of the carbon cathode in Zn-ion hybrid device (a) before and (b) after 200000 cycles. Figure S20. (a) pH values of 3 M Zn(CF3SO3)2 and HCF3SO3, (b) GCD curve at 0.5 A g -1 , and (c) relastionship between capacities of the carbon-based Zn-ion device and the pH values of HCF3SO3 electrolytes. (d) Ex situ high-resolution O 1s XPS spectra of the carbon cathodes using HCF3SO3 electrolytes with different pH values at the discharging state of 0 V.Figure S21. Ex-situ XPS spectra of Zn 2p.Figure S22. XRD patterns of carbon superstructure cathode at different charge/discharge states.Figure S23. Elemental mapping images of carbon cathode at five representative discharging/charging moments (A, B, C, D, and E). Table S7. X-ray electron diffraction spectroscopy data of carbon cathode corresponding to various stages of the discharging/charging courses shown in Figure S23.

Figure S23 .

 S23 Figure S16. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a) GCD curves at 0.5 A g -1 ,(b) the capacity and energy density of the device 2 calculated by the integral area of the GCD curve at 0.5 A g -1 , and (c) comparison of electrochemical performance of three devices. Figure S17. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a, c, e) GCD curves and (b, d, f) rate performances. Figure S18. Investigation of the capacitive effect and diffusion-controlled energy storage behaviors of the device 2: (a) CV curves. (b) The fitting plots between logi and logv at the anodic peaks (bO) and the cathodic peaks (bR). (c) Normalized capacity contribution at different scan rates. Figure S19. SEM images of the carbon cathode in Zn-ion hybrid device (a) before and (b) after 200000 cycles. Figure S20. (a) pH values of 3 M Zn(CF3SO3)2 and HCF3SO3, (b) GCD curve at 0.5 A g -1 , and (c) relastionship between capacities of the carbon-based Zn-ion device and the pH values of HCF3SO3 electrolytes. (d) Ex situ high-resolution O 1s XPS spectra of the carbon cathodes using HCF3SO3 electrolytes with different pH values at the discharging state of 0 V.Figure S21. Ex-situ XPS spectra of Zn 2p.Figure S22. XRD patterns of carbon superstructure cathode at different charge/discharge states.Figure S23. Elemental mapping images of carbon cathode at five representative discharging/charging moments (A, B, C, D, and E). Table S7. X-ray electron diffraction spectroscopy data of carbon cathode corresponding to various stages of the discharging/charging courses shown in Figure S23.

Figure S3 .

 S3 Figure S3. (a) Elemental mapping images of C, N and O and (b) FI-IR spectra for carbon

Figure S4 .

 S4 Figure S4. GCD profiles of the assembled supercapacitors based on carbon superstructures

Figure S5 .

 S5 Figure S5. The capacitance vs. square root of half-cycle time.

Figure S6 .

 S6 Figure S6. Capacitance contribution from fast and slow kinetics at (a) 10 and (b) 500 mV s -1 .

Figure S7 .

 S7 Figure S7. EIS spectra of the devices with various mass loadings of active materials.

Figure S8 .

 S8 Figure S8. Ultrarapid charge-storage kinetics of the assembled supercapacitors under two mass loadings of 25 and 50 mg cm -2 in H2SO4 electrolyte. (a, b) Capacitance contribution. (c, d) The

Figure S9 .

 S9 Figure S9. (a) Long-term cycling stability of carbon supercapacitors at 100 A g -1 over 200,000

Figure S10 .

 S10 Figure S10. (a) Nyquist plots, (b) XPS spectra and (c) high-resolution O 1s of the carbon electrode with 10 mg cm -2 after long-term cycling test.

Figure S11 .

 S11 Figure S11. Electrochemical performances of the assembled carbon-based supercapacitors

Figure S12 .

 S12 Figure S12. Comparison of electrochemical properties in different electrolytes. (a) Ragone

Figure S13 .

 S13 Figure S13. Side views of the electron density difference for one H ion adsorbed in carbon

Figure S14 .

 S14 Figure S14. The diffusion paths of H ions in different models.

Figure S15 .

 S15 Figure S15. Top view of H ion diffusion in N-5 doping structure (path 1) and the corresponding

Figure S18 .

 S18 Figure S18. Investigation of the capacitive effect and diffusion-controlled energy storage

Figure S19 .

 S19 Figure S19. SEM images of the carbon cathode in Zn-ion hybrid device (a) before and (b) after

Figure S20 .

 S20 Figure S20. (a) pH values of 3 M Zn(CF3SO3)2 and HCF3SO3, (b) GCD curve at 0.5 A g -1 , and

Figure S23 .

 S23 Figure S23. Elemental mapping images of carbon cathode at five representative

Table S6 .

 S6 Calculated ion resistance parameters. Figure S13. Side views of the electron density difference for one H ion adsorbed in carbon skeleton. Figure S14. The diffusion paths of H ions in different models.

Table S2 .

 S2 SBET

	Time	SBET	N	O	N-6+N-5	O-1	EHS a	Cm
	(min)	(m 2 g -1 )	(wt.%)	(wt.%)	(%)	(%)	(wt.%)	(F g -1 )
	1	1249	6.49	6.92	55.5	34.1	5.96	302
	30	1466	7.37	7.64	65.3	35.2	7.68	329
	60	1662	8.07	7.01	67.8	34.8	7.91	369
	120	1668	8.14	7.28	66.5	40.3	8.35	415
	180	1993	10.22	5.04	71.9	69.1	10.83	468
	360	1913	7.99	7.81	66.6	43.4	8.71	458
	a EHS (wt.%) = (N-6 + N-5) × N% + O-1 × O%.

, heteroatom contents, relative contents of N-6/N-5 and O-1 species, the contents of effective heteroatomic species (EHS) and electrochemical capacitances (Cs) of carbon superstructures based on TT-DQ polymers at different polymerization times.

Table S6 .

 S6 Calculated ion resistance parameters.

	State	Voltage (V) Rs (Ω)	Rct (Ω)	σ (Ω s -0.5 ) DH + (cm 2 s -1 ) × 10 -8
		1.0	0.31	0.81	0.96	1.23
		0.8	0.23	0.73	0.87	1.50
	Discharge	0.6	0.21	0.67	0.83	1.65
		0.4	0.20	0.65	0.79	1.82
		0.2	0.19	0.58	0.74	2.07
		0	0.18	0.42	0.64	2.77
		0.2	0.19	0.59	0.76	1.97
		0.4	0.22	0.60	0.82	1.69
	Charge	0.6	0.23	0.65	0.88	1.47
		0.8	0.25	0.67	0.92	1.34
		1.0	0.29	0.84	0.98	1.18

Table S7 .

 S7 X-ray electron diffraction spectroscopy data of carbon cathode corresponding to various stages of the discharging/charging courses shown in Figure S23.

	Element (wt.%)	A	B	C	D	E
	Zn	1.03	19.09	28.44	21.78	0.98
	S	0.49	2.33	4.98	3.41	0.24
	F	1.47	9.86	10.34	8.71	1.04
	O	70.42	52.20	44.87	50.97	71.23
	C	25.50	16.38	10.53	14.02	25.80
	N	1.09	0.14	0.84	1.11	0.71

Acknowledgements

This work is financially supported by the National Natural Science Foundation of China (Nos. 21875165, 51772216, and 21905207), the Science and Technology Commission of Shanghai Municipality, China (20ZR1460300, 14DZ2261100), Zhejiang Provincial Natural Science Foundation of China (No. LY19B010003), and the Fundamental Research Funds for the Central Universities. The authors are grateful to the University of Strasbourg and the CNRS.

Received: ((will be filled in by the editorial staff))

Revised: ((will be filled in by the editorial staff))

Figure S17. Repeated electrochemical experiments on three identical assembled Zn-ion devices: (a, c, e) GCD curves and (b, d, f) rate performances.

Self-Assembled Carbon Superstructures Achieving Ultra-Stable and Fast Proton-Coupled Charge Storage Kinetics

Supporting Information Supporting Information is available from the Wiley Online Library or from the author.

Conflict of Interest

The authors declare no conflict of interest.

Supporting Information

Self-Assembled Carbon Superstructures Achieving Ultra-Stable and Fast Proton-Coupled Charge Storage Kinetics Ziyang Song, Ling Miao, Laurent Ruhlmann, Yaokang Lv, Dazhang Zhu, Liangchun Li, Lihua Gan, and S2. SBET, heteroatom contents, relative contents of N-6/N-5 and O-1 species, the contents of effective heteratomic species (EHS) and electrochemical capacitances (Cs) of carbon superstructures based on TT-DQ polymers at different polymerization times.

Section S4. Electrochemical Charge Storage of Carbon-Based

Supercapacitors.

Synthesis of Carbon Superstructure.

0.92 g (5 mmol) of 2,4,6-trichloro-1,3,5-triazine (TT) dissolved in acetonitrile (50 mL) was added into a mixture of 1.79 g (7.5 mmol) 2,6-diaminoanthraquinone (DQ) and 50 mL acetonitrile at 80 °C under stirring for 0.5-3 h. The TT-DQ polymer was collected by filtration, washing, and drying, followed by a one-step carbonization/activation using sodium cyanate as the activator (1:1, w/w) under N2 atmosphere at 800 °C (3 °C min -1 ) for 2 h to yield the carbon superstructures. For comparison, the carbons were also prepared under the same synthesis steps except addition of 4.2 mL triethylamine (TEA).

Characterization.

The sample morphologies were observed using scanning electron microscopy (SEM, Hitachi S-4800) and transmission electron microscopy (TEM, JEM-2100). sorption measurements were carried out using a Micromeritics apparatus (ASAP 2460) at the liquid nitrogen temperature (-196 °C). The surface area and pore size distribution were calculated using the Brunauer-Emmett-Teller (BET) equation and the nonlocal density functional theory equilibrium model. The surface chemistry was studied by an X-ray photoelectron spectrometer (XPS, AXIS Ultra DLD). Fourier-transformed infrared spectrum (FT-IR) was collected on a Thermo Nicolet NEXUS spectrometer. The material structure was characterized by X-ray diffraction (XRD, Bruker D8 advance powder diffractometer with a Cu Kα radiation source).

Electrochemical Evaluation.

Symmetric Supercapacitors. The working electrodes were prepared by pressing a slurry mixture containing carbon materials (80 wt%), graphite (10 wt%), and polytetrafluoroethylene (10 wt%) onto the stainless-steel sheet, and then dried at 80 °C (the mass loading of the active substance is about 10 mg cm -2 ). The 2016 coin-type cells were assembled by stacking two same

DFT Calculation.

The spin-polarized DFT calculations were performed by employing Vienna Ab initio Simulation Package (VASP). 1 The projector-augmented wave (PAW) pseudopotentials 2 with a plane-wave cutoff of 520 eV and Perdew-Burke-Ernzerhof (PBE) function 3 of the generalized gradient approximation (GGA) were adopted to model the electron exchange-correlation interactions. The convergence criterion for the structural optimizations set to be 1×10 -5 eV, and all atomic structures were allowed to be relaxed until the residual forces on each atom dropped below 0.02 eV Å -1 . The geometric optimization was performed by the 3×3×1 Monkhorst-Pack k-point mesh. A supercell of graphene containing 6×6 unit cells with a vacuum region of 20 Å thickness was created to ensure negligible interaction between slabs for describing the N/O codoped carbon systems. The adsorption energy was calculated based on the form:

where EH/carbon, Ecarbon, and EH denote energies of carbon systems with and without H adsorption, and the energy of single H atom in bulk structure, respectively. The more negative the adsorption energy values signify the stronger the H adsorption strength on the carbon systems.

To describe the bonding nature of H adsorbed on doped carbon systems and charge transfer between them in detail, the charge density differences of H absorbed on the constructed carbon structures were calculated by subtracting the charge densities of the H atom and carbon substrates from the corresponding compounds.

The barriers of H ion diffusion on pyrrole-N graphene systems were calculated using the climbing image nudged elastic band (CI-NEB) approach. 4 Bader charge calculations were performed to analyze the charge transfer and the interaction intensity between H and N/Osubstituted active sites. The Dunn's method was employed to quantify the capacitance contribution from fast-kinetic processes (including electrical double-layer capacitive processes and surface rapid redox reactions) and slow-kinetic processes (redox reactions that are diffusion-controlled). The charge-storage kinetic information can be collected by analyzing the relationship between current (i) and the scan rate (v), which can be expressed as the following:

where the k1 and k2 are constants, k1v accounts for the current density contributed from fastkinetic process. The second term k2v 1/2 corresponds to the current density associated with slowkinetic (or diffusion-limited) process. Dividing v 1/2 on both sides of the equation yields:

Therefore, i/v 1/2 and v 1/2 are expected to generate a linear relationship, the capacitance contribution from fast/slow kinetics can be differentiated by linear fitting. The slope corresponds to k1 and the y-intercept equals k2. By repeating the above steps for other potentials and scan rates, the respective capacitance contribution from fast and slow reactions can be quantitatively mapped out. The ratio of fast capacitance to total capacitance equals the ratio of the area of the marked region to the area of the total CV region. The electron transport and ion diffusion resistivity were analyzed with EIS based on the following forms:

where τ: relaxation time constant (s);

𝑓: knee frequency (Hz);

Z': real part of impedance (Ω);

𝜔: angle frequency (rad s -1 ); σ: diffusion resistance (Ω s -0.5 );

Rs: ohmic resistance between the electrode and electrolyte (Ω);

Rct: charge transfer resistance (Ω);

n: electron transfer numbers per molecule during electron reaction; D: ion diffusion coefficient (cm 2 s -1 );

A: surface area of electrode (cm 2 ); R: gas constant (8.314 J mol -1 K -1 );

T: Kelvin temperature (293.15 K);

C: molar concentration of electrolyte (mol L -1 );

F: Faraday constant (96485 C mol -1 ).

Section S6. Electrochemistry Characterization of the Assembled Zn-Ion

Device. Following the charge process, the peak feature undergoes a reverse variation trend.


Marie Vayer

Shaofei Zhang

Joseph Moran

David Leboeuf

Rapid and Mild Metal-Free Reduction of Epoxides to Primary Alcohols Mediated by HFIP

Keywords: epoxides, hydrogenolysis, hexafluoroisopropanol, Brønsted acid, (hetero)cycles

The reduction of epoxides is a powerful tool to access anti-Markovnikov alcohols, but reported methods are poorly compatible with strongly electronically deactivated substrates. Here, we describe a general method for the linear-selective reduction of styryl oxides incorporating strong electron-withdrawing groups. The method remains compatible with more traditional epoxide motifs, such as aliphatic and electron-rich styrene oxides. Other (hetero)cycles such as oxetanes, tetrahydrofurans, aziridines and cyclopropanes can also be reductively opened. This user-friendly reaction relies on the combination of a Brønsted acid catalyst and hexafluoroisopropanol as a solvent and thus, in contrast to existing epoxide reduction methods, does not require anhydrous reagents or an inert atmosphere. The generated primary alcohols can be conveniently functionalized in situ by a dehydrative Friedel-Crafts arylation without pre-activation.

 Notwithstanding their undeniable utility and wide scope, these methods suffer either from regioselectivity issues or from functional group tolerance. To circumvent those issues, the direct hydration of alkenes has been described, 5 featuring, for instance, triple relay catalysis, 6 visible-light-mediated protocols, 7 and metal-oxo enzymes. 8 However, these methods are mostly limited to terminal styrene oxides.

 Although the overall reaction scope of these methods was broad, neither were reported to be compatible with highly deactivated styrene oxides bearing a electron-withdrawing group stronger than a trifluoromethyl 18 nor to reduce (hetero)cycles beyond epoxides. Lambert's method operates under mild conditions (ambient temperature and pressure), but regiocontrol is incomplete in the case of aliphatic epoxides. Recently, an elegant and mild Scheme 1. Approaches toward the synthesis of primary aliphatic alcohols.

 However, this method only provided moderate yields (41-51%) for deactivated styrene oxides, while aliphatic epoxides exclusively led to Markovnikov alcohols. In summary, while several protocols have been developed, each with their own

advantages and limitations, a general and user-friendly method for epoxide reduction is still missing.

In hexafluoroisopropanol (HFIP), a solvent known for its Hbond donating ability, 20 the strength of catalytic Brønsted acids is drastically increased, rendering electronically deactivated substrates more reactive. 21 We recently reported an efficient, practical, and broadly applicable Friedel-Crafts arylation of epoxides, including highly deactivated styrene oxides, using catalytic triflic acid (TfOH) in HFIP. [START_REF] Zhang | Unlocking the Friedel-Crafts Arylation of Primary Aliphatic Alcohols and Epoxides Driven by Hexafluoroisopropanol[END_REF][START_REF] Li | J. Friedel-Crafts Alkylation of Arenes with Epoxides Promoted by Fluorinated Alcohols or Water[END_REF] The formed alcohols could undergo a second arylation to access diaryl-and triarylalkanes without pre-activation, [START_REF] Li | Electrochemically Enabled, Nickel-Catalyzed Dehydroxylative Cross-Coupling of Alcohols with Aryl Halides[END_REF] although this is less efficient when two different nucleophiles were employed. Herein, we demonstrate that this simple catalytic system can be applied to the reduction of epoxides, including electronically deactivated substrates, to rapidly afford the corresponding anti-Markovnikov alcohols at room temperature (Scheme 1C). This practical transformation exhibits broad functional group tolerance, notably towards strong electron-withdrawing groups, and can also be applied to the reductive ring-opening of other (hetero)cycles, such as oxetanes, cyclopropanes and aziridines. Moreover, by coupling epoxide reduction to Friedel-Crafts reactions in the same pot, this work overcomes existing limitations in the dehydrodiarylation of epoxides.

Our optimization studies started with para-nitrostyrene oxide 1a as a model substrate using TfOH as a catalyst (5 mol%) in HFIP (0.2 M) as a solvent (Table 1, see also the Supporting Information for full details). Triethylsilane (Et3SiH) was initially chosen as a hydrogen donor due to its compatibility with HFIP in hydrosilylation reactions [START_REF] Zhan | Chemoselective Hydrosilylation of the α,β-Site Double Bond in α,β-and α,β,γ,δ-Unsaturated Ketones Catalyzed by Macrosteric Borane Promoted by Hexafluoro-2propanol[END_REF] and, more generally, in acidic media. 26 Using an excess of Et3SiH (2 equiv), the target product 2a was obtained in 86% yield within 30 minutes at ambient temperature (entry 1). Other hydrogen donors such as H2 and pinacol borane (HBPin) were tested but did not generate 2a (entries 2 and 3). The catalyst loading could be reduced to 1 mol% or even 0.1 mol% without any drop in yields (entries 4 and 5). However, at 0.1 mol% loading, a prolonged reaction time (2 h) was required to fully convert the silyl-protected intermediate into 2a. Increasing the concentration proved to be detrimental to the yields (entries 6 and 7). The combination of 1 mol% TfOH and 1.5 equiv. of Et3SiH was optimal in terms of efficacy (91%) and reaction time (30 min) (entry 8). Of note, the reaction was accomplished on a larger scale (7.5 mmol) to deliver 2a in 88% yield (1.1 g). [START_REF]Of note, regarding reactions on large scale, HFIP can be simply recovered by distillation, offsetting[END_REF] Common solvents (CH2Cl2, MeNO2 and toluene) and O-methyl hexafluoroisopropanol (HFIPMe) were also examined but did not provide 2a in synthetically useful yields (entries 9-12), highlighting the critical role of HFIP in this reaction. Lastly, a control experiment was performed in the absence of TfOH and no product was observed (entry 13). With optimized conditions in hand, we explored the scope of the reaction using a large variety of epoxides (Scheme 2). Monosubstituted styrene oxides were smoothly converted into the target primary aliphatic alcohols in high yields (up to 91%).

In particular, the reaction was compatible with highly electronically deactivated styrene oxides containing perfluoro, trifluoromethyl, cyano, amide, ester, and ketone groups. In the latter case, a product resulting from the reduction of the ketone in the alkane was nonetheless observed in 20% yield. The transformation was also extended to aliphatic epoxides to provide the anti-Markovnikov alcohols in good yields (51-91%). In a limited number of cases (2s and 2t), some amounts of Markovnikov alcohols were detected. On the other hand, one limitation of our method concerns the reactivity of glycidyl ether derivatives, whose reduction led mainly to the branched alcohol (2u). This might be explained by the coordination of the promoter system to both oxygen functionalities, favoring the direct addition of the silane to the epoxide at the less sterically hindered position. The reaction was also compatible with 1,1disubstituted epoxides (aryl-alkyl and alkyl-alkyl substituents) to exclusively afford primary alcohols in yields up to 92% (2v-2ai). The methodology was successfully applied to derivatives of bioactive molecules such as pentoxifylline (2ah, 65%) and rotenone (2ai, 57%). 1,2-Disubstituted and 1,1,2-trisubstitued epoxides were amenable to this process to provide the corresponding secondary alcohols in 55-85% yields (2aj-2an).

During those investigations, we noticed, the formation of a side product resulting from a 1,2-Me shift, which was directly correlated to the substitution pattern of the styrene oxide. This type of rearrangement could be suppressed with less electrondeficient 1-phenylpropylene oxide (2am) as well Scheme 2. Scope of the reaction.

a TfOH (20 mol%) and Et3SiH (3 equiv). b Yield determined by 1 H NMR using mesitylene as an external standard. as with trisubstituted epoxides (2an). Moving beyond epoxides, the method served as a rare metal-free protocol for the reduction of related but underdeveloped aryl-substituted (hetero)cycles such as oxetanes (2q), 19,28 tetrahydrofurans (5), 19,29 aziridines (7), [START_REF] Chandrasekhar | Reductive Opening of Aziridines with Polymethylhydrosiloxane[END_REF] and cyclopropanes (9), 31 generating the corresponding ring-opening products in high yields (80-98%). Since primary alcohols were successfully produced with our strategy and based on our previous work on the Friedel-Crafts arylation of primary aliphatic alcohols, [START_REF] Zhang | Unlocking the Friedel-Crafts Arylation of Primary Aliphatic Alcohols and Epoxides Driven by Hexafluoroisopropanol[END_REF] we next examined a one pot method for the reductive ring-opening arylation of epoxides (Scheme 3). Due to the importance of the 1,1,2-triarylethane and 1,2-diarylalkane motifs in life sciences, [START_REF] Tolstoy | Iridium-Catalyzed Asymmetric Hydrogenation Yielding Chiral Diarylmethines with Weakly Coordinating or Noncoordinating Substituents[END_REF] the reactivity of 1,1-disubstituted epoxides was initially studied using p-xylene as an arene nucleophile for the second step. First, the reaction was conducted under the conditions designed for the reductive ring-opening. After the reaction was completed, 10 mol% TfOH and 5 equivalents of p-xylene were added to the reaction mixture, which was typically heated to 80 °C for 48 h. The target products were thus obtained in 59 to 94% yields (10a-10f) via a phenonium ion intermediate. The formation of regioisomers was observed as the nucleophile can attack at either the internal (major product) or the terminal position (minor product) of the phenonium ion intermediate. The major advantage of this reaction sequence is that it overcomes the limitations encountered with our previous work on the dehydrodiarylation of epoxides, where yields were modest, or even low in the case of aliphatic epoxides, when two different nucleophiles were used. The reaction was also found to be compatible with mono-substituted styryl oxides, giving access to the corresponding products 11a-11c in good yields (50-73%). Lastly, we demonstrated that an intramolecular Friedel-Crafts alkylation could be accomplished following the reduction of epoxide 12, affording tetrahydronaphthalene 13 in 62% yield.

We then investigated the mechanism of this transformation (Scheme 4). Based on the reactivity of epoxides with Brønsted acids, 33 we hypothesized that deactivated styrene oxide 1a is first protonated by TfOH, whose acidity is augmented through its coordination to HFIP. This increase in acidity promotes the Meinwald rearrangement of the epoxide to the corresponding aldehyde 14. This aldehyde would be further reduced by the silane to access silyl ether 15, which would be deprotected in situ to deliver phenylethanol 2a under our acidic reaction conditions. A series of experiments was carried out to evaluate this proposal (Scheme 5B). In the absence of triethylsilane, aldehyde 14 was obtained as sole product in 81% yield (Eq. 1). When subjected to our standard conditions, 14 yielded the target alcohol 2a (Eq. 2). Of note, the reduction step did not work without TfOH, showing its importance for each step. The reaction in the presence of deuterated triethylsilane (Et3SiD) furnished the corresponding product [D]-2a, which is consistent with aldehyde 14 being a crucial intermediate (Eq. 3). Lowering the loading of TfOH to 0.1 mol% allowed us to observe the formation of silyl ether 15 in a 1:1 mixture with 2a after 30 min before it fully converted into 2a after 2 h (Eq. 4). The reaction was also performed with other representative epoxides (electron-rich styrene oxide, 1,1-disubstituted epoxide and mono-substituted alkyl epoxide) in the presence of Et3SiD to evaluate whether the substitution pattern has an influence on the reaction pathway (Scheme 5.C). In the case of 1q and 1ae, the reaction led to similar results as 1a (Eq. 5 and Eq.6), which is consistent with a Meinwald rearrangement. On the other hand, in the case of electron-rich styrene oxide (1o), deuteration was observed at the benzylic position ([D]-2o), suggesting that the stabilized carbocation intermediate underwent a direct reduction. In parallel, we conducted a similar experiment with oxetane 3, tetrahydrofuran 4 and Scheme 3. One pot sequential reductive ring-opening of epoxides/Friedel-Crafts arylation reaction a Yield determined by 1 H NMR using mesitylene as an external standard.

Scheme 4. Mechanistic investigations aziridine 6. In the case of 4 and 6, we observed deuteration exclusively at the benzylic position, in the same vein as with 1o.

In turn, a mixture of several products was obtained with 3, making it difficult to identify a clear mechanism. Lastly, to determine whether the Meinwald rearrangement occurred through a concerted mechanism or a carbocation, we compared the reactivity of diasteromeric derivatives of (+)-isopulegol (Eq. 10 and Eq. 11). In both cases, 3,6-dimethyloctahydrobenzofuran 17, resulting from the cyclization of the reaction intermediate, was obtained with a similar dr, consistent with the formation of a carbocation during the first step of the Meinwald rearrangement.

In conclusion, we have developed a practical strategy to selectively access anti-Markovnikov alcohols via a reductive ring-opening of epoxides. The mechanistic studies suggest an isomerization/hydrosilylation process promoted by the association of TfOH/HFIP in the presence of triethylsilane. This transformation occurs under mild conditions and exhibits a broad substrate scope, including aryl epoxides containing strong electron-withdrawing groups and derivatives of bioactive molecules. In addition, the reaction was extended to oxetane, tetrahydrofuran, aziridine and cyclopropane as electrophiles.

Finally, a one-pot epoxide reduction/dehydroarylation sequence was disclosed, leading to the rapid preparation of complex arylated products.

Table 1 .

 1 Optimization of reaction conditions for the formation of phenylethanol 2a.

	Entry Variation from standard conditions a	Yield (%)
	1	none	86
	2	H2 (20 bar) instead of Et3SiH	-
	3	HBPin instead of Et3SiH	-
	4	1 mol% of TfOH instead of 5 mol%	83

a Reactions performed in a sealed tube. b 2 h reaction time. c 7.5 mmol scale.

ACKNOWLEDGMENT

D.L. and J.M thank the CNRS. The authors thank Wahnyalo Kazone for HRMS analysis.

Funding Sources

This work was supported by the Interdisciplinary Thematic Institute ITI-CSC via the IdEx Unistra (ANR-10-IDEX-0002) within the program Investissement d'Avenir. S.Z. thanks the China Scholarship Council for a fellowship.

ASSOCIATED CONTENT Supporting Information.

The Supporting Information is available free of charge via the Internet at http://pubs.acs.org. Experimental procedures, optimizations studies, mechanistic studies, characterization data; copies of NMR spectra (PDF)

AUTHOR INFORMATION

Author Contributions

The manuscript was written through contributions of all authors.

Notes

The authors declare no competing financial interest.


Jing Yi

Harpreet Kaur

Wahnyalo Kazöne

Sophia A Rauscher

Louis-Albin Gravillier

Prof. Dr Kamila B Muchowska

Joseph Moran
email: moran@unistra.fr

] J Yi

Dr L.-A Gravillier

A Nonenzymatic Analog of Pyrimidine Nucleobase Biosynthesis

Keywords:

Metabolic theories for the origin of life posit that inorganic catalysts enabled self-organized chemical precursors to the pathways of metabolism, including those that make genetic molecules. Recently, experiments showing nonenzymatic versions of a number of core metabolic pathways have started to support this idea. However, experimental demonstrations of nonenzymatic reaction sequences along the de novo ribonucleotide biosynthesis pathways are limited.

Here we show that all three reactions of pyrimidine nucleobase biosynthesis that convert aspartate to orotate proceed at 60 ºC without photochemistry under aqueous conditions in the presence of metals such as Cu 2+ and Mn 4+ . Combining reactions into one-pot variants is also possible. Life may not have invented pyrimidine nucleobase biosynthesis from scratch, but simply refined existing nonenzymatic reaction channels. This work is a first step towards uniting metabolic

Thinking about the chemical origins of life is often divided along --assumes that self-replicating genetic polymers, likely RNA, emerged directly from a prebiotic chemistry bearing little resemblance to biosynthetic pathways. [ 1 ] From that perspective, early prebiotic chemistry is simply a tool to furnish building blocks for a later self-organized process. A central challenge for this vision of prebiotic chemistry is the direct, robust and high-yielding synthesis of ribonucleotides or deoxyribonucleotides by any plausible means. Experimental work along these lines has been arguably the major thrust of the field for the past 50 years, [ 2 ] with recent experimental work from Sutherland, [3] Carell, [4] Powner, [5] Benner, [6] and Trapp [7] . However, without overlooking the undeniable importance of ribonucleotides and RNA in the origin of life, [8] starting in the late 1980s -- [9,10,11,12] This approach considers the origin of life to have involved the spontaneous onset of a self-organized reaction network, which was driven into existence by a thermodynamic need to relax geochemical redox gradients. The initial catalysts enabling the self-organized reactivity would have been minerals, clays and metals, but certain organics produced by the network could additionally feed back as catalysts to reinforce the existing reactions and to enable new ones. [13,14,15] Such a reaction network would have been historically continuous with biological metabolism. Furthermore, because complex systems, such as metabolism, are difficult to disrupt and rewrite, certain energetic and chemical similarities should exist with metabolism today. From this alternative perspective, ribonucleotides and their oligomers would have been produced by the prebiotic reaction network, possibly initially in small quantities, but gained prominence within it because they offered a critical catalytic or regulatory function within the existing self-organized chemistry. [12] Viewed from this angle, a central challenge of prebiotic chemistry is to figure out what the conditions for such self-organized chemistry would have been. One way towards this goal is to search for conditions that recapitulate nonenzymatic variants of core metabolic reactions and processes, [16,17] including those for the synthesis of genetic molecules. [ 18 ] Multiple, possibly very different, conditions might be found to enable any particular reaction or pathway without enzymes, and some of these conditions may have no relevance to the origin of life. However, this strategy should eventually identify conditions that enable a larger system to self-organize. [17] Experimental efforts in this direction [19] have thus far focused on metal-catalyzed analogues of carbon fixation pathways, [START_REF] Huber | W chtersh user[END_REF]21,22,23,24] amino acid [25,26,27] and cofactor [ 28 , 29 ] biosynthesis, and sugar metabolism [ 30 , 31 , 32 , 33 ] . Investigations into purely chemical conditions that trigger reactions of ribonucleotide biosynthesis in a prebiotic context have been limited, as we will discuss below.

Ribonucleotides are biosynthesized in two general ways: by salvage pathways that regenerate ribonucleotides after they degrade, and by de novo pathways that build them up from scratch starting from amino acids, C1 compounds and phosphoribosylpyrophosphate (PRPP), an activated form of ribose-5-phosphate. The first three steps of de novo pyrimidine ribonucleotide biosynthesis are illustrated by the black arrows in Scheme 1. First, aspartate (ASP) reacts with carbamoyl phosphate (CAP) to give carbamoyl aspartate (CAA), catalyzed by carbamoyl phosphate synthetase. [START_REF] Mcmurry | The Organic Chemistry of Biological Pathways[END_REF] CAA then undergoes a dehydrative cyclization to give dihydroorotate (DHO) catalyzed by Scheme 1. The first three steps of de novo pyrimidine ribonucleotide biosynthesis convert aspartate (ASP) to orotate (ORO), as shown by the black arrows. Additional reactions observed in this report are described by blue arrows.

dihydroorotase. DHO is oxidized to orotate (ORO) by various electron-accepting cofactors, catalyzed by dihydroorotate dehydrogenase. Later on in the pathway, not illustrated in Scheme 1, ORO couples with PRPP to give -monophosphate, and, in subsequent steps, the canonical pyrimidine ribonucleotides uridine--monophosphate and cytidine--monophosphate. The conversion of ASP to ORO is therefore a key biosynthetic bottleneck in the formation of pyrimidine ribonucleotides.

Much prebiotic chemistry has been described that conceptually resembles ribonucleotide biosynthesis, [2] but little that involves precisely the same reactions and substrates. However, if metabolism is derived from self-organized chemistry, deviations from the reactions or substrates it uses, even if they lead to a biological product, might lack relevance to prebiotic chemistry. As for reports that specifically recapitulate ribonucleotide salvage pathways, Jaber, Georgelin and coworkers examined the nonenzymatic formation of adenosine monophosphate from adenine and phosphoribosylpyrophosphate (PRPP). [START_REF] Akouche | [END_REF] Chemistry that roughly resembles de novo pyrimidine nucleobase biosynthesis has also been reported, but not for the biological substrates along the entire path. [18,36,37,38] Yamagata used urea, rather than CAP, and UV light, rather than a chemical oxidant, at 80-90 ºC. [38] In that study, the photooxidation of DHO to ORO was particularly challenging, reaching <1% yield after 2.5 days and declining thereafter. It still remains unclear whether all the biological transformations of pyrimidine ribonucleobase biosynthesis can occur without enzymes and, crucially, without photochemistry, as none of the nonenzymatic analogues of the other pathways described above depend on light. [START_REF] Huber | W chtersh user[END_REF][21][22][23][24][25][26][27][28][29][30][31][32][33] Here we examine these first three key steps experimentally and find that they all occur nonenzymatically in water at 60 ºC without the need for UV light.

We began our investigations by exploring the nonenzymatic reaction between ASP, derived from the non-enzymatic reductive amination of oxaloacetate, [22] and CAP to give CAA. Previously, CAP and CAA have been obtained in a prebiotic context starting from cyanate or from urea (via cyanate), [38,39,40,41] however the use of CAP to prepare CAA, as in the biological pathway, has not yet been studied. The reaction between ASP (8.5 mM) and CAP (8.5 mM) was assayed over a pH range of 3-9 and a temperature range of 0-60 ºC. Acidic conditions were found to be ineffective. The optimal conditions were found to be pH 8 and 60 ºC, giving 37% yield after 16 h, as determined by quantitative 1 H NMR by integrating against dimethyl sulfone (DMS) as an internal standard. The identity of the product was additionally confirmed by LC-QTOF-MS analysis of the reaction mixture through comparison with an authentic sample. The use of a two-fold excess of CAP relative to ASP gave CAA in 63% yield after 16 h (Figure 1A). When the initial concentration of ASP was increased from 8.5 mM to 21 mM (still with a 2:1 ratio of CAP to ASP), the yield of CAA increased to 74%. Full optimization details can be found in Table S1. From a mechanistic standpoint, cyanate is known to be produced, along with phosphate, by thermal fragmentation of CAP and is therefore a likely intermediate in the reaction. [42,43] In line with this proposal, the use of pH 8 phosphate buffer, rather than water adjusted to pH 8, decreased the yield of CAA to 10% (Table S1, entry 10), which might be explained by a less favorable equilibrium between CAP and cyanate in the presence of excess phosphate.

Encouraged by this result, we next explored the nonenzymatic dehydrative cyclization reaction of CAA to DHO. It should be noted that this reaction is endergonic and at pH 7.4 at 37 ºC the enzyme catalyzed process favors CAA over DHO by a factor of 16.6 at equilibrium. [44] Thus, low yields of DHO are to be expected under similar conditions. The reaction was assayed over a pH range of 1-9 and a temperature range of 20-60 ºC. The products were quantified by 1 H NMR and confirmed by LC-QTOF-MS in the same way as described earlier. At pH values near the lower end of this range, the reaction did not produce any DHO, but instead gave rise to the 5-membered product, hydantoin-5-acetate (HAA). This result is similar to that observed in a non-prebiotic context during the total synthesis of orotic acid. [41] A new screen was therefore conducted across the same range of conditions but in the presence of a panel of metal salts and oxides. Zn 2+ , Cu 2+ and Fe 3+ produced a small amount of DHO at the higher pH values, with Cu 2+ being the most selective for DHO over HAA. For example, the reaction of CAA with CuSO4 (40 mol%) at 60 ºC, pH 8 after 16 h gave DHO in 1% yield as the only observed cyclization product (Figure 1B). At lower pH values the DHO obtained increased, but HAA became the major product due to the acidcatalyzed background reaction (Table S2). For example, at pH 2 in the presence of Cu 2+ , DHO was obtained in 3% yield together with 25% of HAA. Increasing the initial concentration of the starting material to 21 mM improved the yield of both products, giving 4% DHO and 40% HAA. [45] We note that Cu 2+ has proven an intriguing additive in a number of different prebiotic contexts. [27,46] We next examined the oxidation of DHO to ORO. Previously, a nonenzymatic version of this reaction had only been observed in <1% yield under direct UV irradiation. [38] A screen was devised to assay oxidants over a pH range of 2-9 and a temperature range of 20-60 ºC. At 60 ºC, two optimal oxidants were found to be H2O2 and MnO2, the prebiotic plausibility of which was recently discussed. [ 47 , 48 ] In the case of H2O2 as oxidant, the reaction worked best at pH 9, giving 34% yield of ORO after 16 h. In the case of MnO2 as oxidant, at pH 3.5, ORO was obtained in 16% yield, together with 2% of uracil (URA) after 16 h. Next, we studied the influence of metal additives on the oxidation. The presence of metal ions inhibited the H2O2 promoted oxidation to ORO. For example, the presence of Cu 2+ reduced the yield to <3% ORO, together with 4% URA. However, in the case of the MnO2 promoted oxidation, a screen of metal ion additives (Fe 2+ , Co 2+ , Ni 2+ , Cu 2+ ) revealed that the presence of Cu 2+ (40 mol%) enhanced the outcome, giving ORO in 51% yield together with 2% URA (Figure 1C). The other metal co-catalysts assayed did not display any enhancing effects (Table S3). Cu 2+ is thus capable of influencing both the cyclization and oxidation steps on the nonenzymatic version of the biological path to ORO.

Given that the cyclization of CAA to DHO occurred in highest yield at lower pH, where it is accompanied by HAA as major product (Table S2), we wondered whether HAA might also be converted to ORO under similar oxidative conditions. Could HAA be oxidized to 1 under plausibly prebiotic conditions, which could then undergo a known rearrangement under alkaline aqueous conditions to give ORO? [41] Exposing HAA to H2O2 did not result in its oxidation under the conditions we tested. In contrast, exposing HAA to MnO2 in the presence of Cu 2+ (40 mol%) at 60 ºC for 16 h indeed resulted in its oxidation to 1 (characteristic singlet at 5.4 ppm in 1 H NMR) and to URA (2%) (Table S4).

Basifying the reaction mixture with NaOH and continued heating for a further 3 h resulted in a decrease in concentration of 1 due to its conversion to ORO (11%) along with hydrolysis to CAA (Figure 1D). Thus, the adventitious conversion of CAA to HAA is not necessarily a dead end, as it can be funneled towards the same end-product, ORO (Scheme 1, blue arrows).

In order to assess the feasibility of a non-photochemical one-pot process mimicking pyrimidine nucleobase biosynthesis, we first attempted to merge the dehydrative cyclization and oxidation steps. Heating CAA in the presence of Cu 2+ at 60 ºC, followed by the addition of MnO2 at 16 h and NaOH at 32 h gave ORO in 2% yield at 35 h. It was later found that the yield could be improved to 13% NMR yield (24% by LC-QTOF-MS) of ORO by lowering the initial reaction pH, along with a 1% yield of URA and 13% of unreacted CAA (Figure 2A). This outcome is in agreement with the aforementioned influence of pH on the cyclization of CAA to DHO and HAA. Next, we examined a one-pot process for the conversion of ASP and CAP to ORO. Heating ASP and CAA (1:2) at 60 ºC at pH 8, followed by the addition of Cu 2+ and HCl at t = 16 h, MnO2 at t = 32 h, and NaOH at t = 48 h gave ORO in 1% NMR yield (4% by LC-QTOF-MS) along with 14% CAA at t = 54 h. Intermediate 1 is notably observed by 1 H NMR in both of the one-pot experiments described in Figure 2, indicating that the pathways proceeding through DHO and through HAA are both occurring. It was also possible to obtain ORO from ASP in one pot by adding all the reagents from the beginning apart from the basification of the reaction at t = 16 h with NaOH, however, the yield decreased to <1% (Table S6, entry 2). NaOH must not be added from the beginning as DHO rapidly decomposes in its presence. Control experiments indicate that the decrease in yield observed when all reagents (other than NaOH) are present from the beginning is due to the decomposition of CAP by Cu 2+ (Table S1, entry 6).

In conclusion, we have uncovered a non-photochemical nonenzymatic analog of pyrimidine nucleobase biosynthesis in which some steps are promoted by metals. Some of the steps are inhibited by metals or by unfavorable pH values, which explains why the one-pot version of this chemistry was helped by timed addition of metals or timed changes in pH. Although pH gradients do exist in certain natural environments, such as hydrothermal vents, [49] we feel it is premature to place this chemistry in a specific geological location. Whether or not the particular set of conditions described here are directly relevant for the origin of life, they nonetheless constitute a proof of principle that this key biological process on the path to genetic molecules could have existed even before enzymes had evolved to catalyze it. In addition to the specific reactions of the biosynthetic pathway shown here, parallel nonenzymatic reactions not found in biology also occur but still eventually arrive at the same biological endpoint: orotate. The conversion of ASP to ORO does not necessarily require metals, especially if a potentially prebiotic alternative oxidant could be found. However, at least at 60 ºC in aqueous solution, [45] only the metal-mediated reaction sequence follows the de novo biosynthetic pathway, passing through DHO. It is this path that carries greater explanatory value when viewed in the framework of the hypothesis that nonenzymatic reactions templated the evolution of the biological pathway. [9][10][11][12][13][14][16][17][18][19] Evolutionary refinement of the redundant branched nonenzymatic reaction network shown in Scheme 1 (both black and blue arrows) would logically result in a streamlined linear pathway like the one found in biology today (black arrows only). [START_REF] Clay | Following submission of this work, a prebiotic synthesis of orotate was reported starting from hydantoin and glyoxylate, which also proceeds through 1. Interestingly, the reaction occurs under conditions similar to the ones reported here (60-80 ºC). As the reaction of glycine with CAP followed by dehydrative cyclization would form hydantoin, just as ASP reacts with CAP to eventually form HAA, that pathway and the two reported here would all be expected to arrive at ORO starting from the amino acids of core metabolism. It remains unclear why only the path passing through DHO was retained in biology[END_REF] In line with this idea, some enzymes still catalyze an equilibrium between CAA, HAA and DHO, [51 ] even though there appears to be no biological use for HAA. The present work can be viewed as a first experimental step toward incorporating genetic molecules into a self-consistent metabolic framework for the origin of life. Preliminary experiments indicate that the N-carbamoylation of ASP with CAP is not selective over other amino acids (Figure S7). However, the potential implications of this observation to a self-organized prebiotic chemistry depends on many factors which are at present difficult to constrain. Future work should investigate to what extent a one-pot nonenzymatic version of this pathway can occur without controlled changes to reaction conditions, and whether the nonenzymatic assembly of pyrimidine ribonucleotides can occur in ways paralleling their de novo biosynthesis. [52]

Entry for the Table of Contents

The biosynthetic reactions that convert aspartate into orotate, the precursor to pyrimidine nucleobases, occur nonenzymatically and without photochemistry at 60 ºC in the presence of metals, giving insight into how these metabolic pathways may have emerged at the origin of life.

Institute and/or researcher Twitter usernames: @MoranLabUdS

Figure 1 . 1 H

 11 Figure 1. Study of single reaction steps. (A) 1 H NMR spectrum of the products of reaction of aspartate ASP and carbamoyl phosphate CAP B) 1 H NMR of the products of cyclization reaction of carbamoyl aspartate CAA. (C) 1 H NMR of the products of oxidative reaction of dihydroorotate DHO. (D) 1 H NMR of the products of oxidative reaction of hydantoin-5-acetate (HAA). Yields were determined by quantitative 1 H NMR with water suppression techniques, integrating against dimethyl sulfone as an internal standard.

Figure 2 .

 2 Figure 2. One-pot formation of pyrimidine bases. (A) 1 H NMR and LC-QTOF-MS of the products of multi-step reaction of carbamoyl aspartate (CAA). (B) 1 H NMR and LC-QTOF-MS of the products of multi-step reaction of aspartate, (ASP) and carbamoyl phosphate (CAP). [M-H] at m/z = 155.0098 was chosen as characteristic fragment for ORO, [M-H] at m/z = 111.0196 was chosen as characteristic fragment for URA.

Acknowledgements

This project has received funding from the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement n° -Curie grant exploring also supported by the Interdisciplinary Thematic Institute ITI-CSC via the IdEx Unistra (ANR-10-IDEX-0002) within the program . J.M. thanks the VW Foundation (no. 96_742) for generous support. J.Y. thanks the China Scholarship Council for a fellowship. We thank Dr. David Leboeuf and Dr. Robert J. Mayer for helpful feedback on the manuscript.