Laura C Loaiza

Monconduit Laure

Seznec Vincent

Towards germanium

layered materials as superior negatives electrodes for Li-, Na-

Introduction

Nowadays, the batteries play a key role in almost all of the technologies that surround human kind. In order to satisfy the increasing demand, the design of more efficient devices with higher energy densities and cycle life is crucial. In this context group 14 elements appear as suitable candidates for anode materials due to their high theoretical capacities. Particularly, Ge forms Li15Ge4 [START_REF] Jung | [END_REF] with 1384 mAh/g and NaGe [2] and KGe [3] with 369 mAh/g. These significant specific capacity values come at the expense of a volume expansion that leads to a capacity fading. Additionally, Ge is less abundant than Si, thus its practical application remains hindered by its high cost. Nevertheless, it presents a series of advantages over silicon as an electrode: i) it allows very fast Li + diffusion, (ca 400 times faster than in silicon) [4,5] and exhibits an electronic conductivity two orders of magnitude larger. [6] ii) Lithiated Ge alloys have a slightly lower volumes than the corresponding Si analogues, hence their associated volumetric expansion is smaller. [7] iii) Ge experiences an isotropic volume expansion that permits a facile stress relaxation; while this process in Si is anisotropic and promotes the formation of cracks in the electrode. [8] Several strategies have been proposed in the literature to mitigate the volume variations in Ge anode electrodes, among them, the reduction of the dimensions to form nanoparticles, nanowires, nanotubes and thin films. [9] Another option are the layered or two-dimensional materials (2D), in which the active surface area is increased and the energy barrier for diffusion is lower. For the group 14 the dimensional diversity is based in the nature of the bonding between atoms, producing Ge with layered structures based on a mix sp 2 -sp 3 bonding with the fourth bond completed by -H or -OH, such in germanane (GeH)n. [10] This last one is obtained from the layered CaGe2 in which the [Ge -] Zintl ion allows the topotactic deintercalation of Ca 2+ while preserving the Ge backbone. [11] This germaniumbased layered material was first reported in 2000 [12,13] and presents several differences compared to its bulk counterpart, for instance it has a direct band gap and exhibit a strong photoluminescence (change in color from the gray-metallic in CaGe2 to red in germanane [12] ), which is directly related with the presence of -OH and -H groups. [14] Hence the nature of the ligands has a repercussion in the physical and chemical properties. This characteristic is absent in most of the Van der Waals compounds due to their neutrality, while for germanane it can be easily achieved by a modification of the synthesis conditions. [15] The germanane layers can be exfoliated into nanosheets (GeNS), by mechanical processes, like scotch tape or sonication. [16,17] These GeNS have buckled honeycomb structures identical to Ge (111) but are easily oxidized. This issue can be addressed by the introduction of covalent bonds improving the chemical and thermal stability. [18] This versatility of germanane sets it as promising candidate for battery applications, not only due to its layered structure and improved electronic conductivity and ion diffusivity but also by its feasibility to be modified to meet certain requirements; properties that undoubtedly would be beneficial for improving the electrochemical performance of Ge-based anodes in batteries. Other applications such as supercapacitors, optoelectronics or catalysis are foresee as well. In this study, the alkali-ion storage properties of germanane were evaluated, the results are very promising with 2150, 495 and 205 mAh/g of reversible capacity for Li, Na and K respectively. The layered morphology of germanane buffers the volume expansion, increases the surface area and lowers the energy barrier for diffusion. [17] These results show the versatility of germanane as anode material for different battery systems, opening the quest on a deeper research and understanding of the layered Ge-based phases.

[a]

Results and Discussion

• CaGe2 The CaGe2 is a Zintl phase with a layered structure consisting of Ge6 rings interconnected to form planes, each Ge atom is bonded to other 3 Ge atoms and completes the octet rule by accepting one electron from the Ca 2+ . Likewise CaSi2, the CaGe2 phase presents several polymorphs (Figure S1). The β-CaGe2 or 6R-CaGe2, that crystallizes in the rhombohedral CaSi2-type (space group R-3m), known for several decades as the only thermodynamically stable polymorph. Recent studies have revealed the existence of the 2H or α-CaGe2 that crystallizes in a hexagonal cell (space group P63mc), its formation is related to the synthesis conditions and is a metastable phase stabilized by the presence of impurities. [19] The 3R-CaGe2 has a rhombohedral unit cell (space group R-3m) and is the most stable polymorph at low temperature, while the 6R stabilizes above 673 K. [19] The aforementioned polymorphs mainly differ by their stacking sequences, the layers are organized in a staggered fashion, and follow the ABAB sequence for 2H-CaGe2, ABC for 3R-CaGe2 and AA'BB'CC' for 6R-CaGe2. [20,21] The stacking compatibility allows the formation of other metastable phases, meaning that the 4H polymorph can be easily formed from the 3R-CaGe2 by the addition of an A' stacking to the matrix. [19][20][21] As observed in the Figure S1, the stacking originates different interlayer distances that are related to the CaGe2 stability, indeed a large interlayer distance leads to a rapid decomposition upon contact with moisture, according to the reaction: [START_REF] Brandt | Silicon Chemistry: From the Atom to Extended Systems[END_REF] CaGe2 + H2O → Ca(OH)2(GeH)2

(1)

This decomposition product contains layers of germanane (GeH)n separated by Ca(OH)2 monolayers with no destructive oxidation of the Ge backbone. The stacking sequence is preserved, although the c parameter is increased due to the bigger size of Ca(OH)2. [20,[START_REF] Vogg | [END_REF] The CaGe2 was synthesized by ball milling, mixing stoichiometric amounts of Ca and Ge followed by an annealing process at 800°C in a sealed tube under Ar. The diffraction pattern and the corresponding Le Bail profile matching are presented in Figure 1-a. The analysis indicates the presence of at least two polymorphs, the 3R and 6R, but other polymorphs could be present. The annealing temperature (800°C) allows the stabilization of both 3R and 6R, although if increased to 950°C only the 6R should be formed. The profile matching provided refined cell parameters of a/b=4.008(2) Å, c=10.320(7) Å and V= 143.64(1) Å 3 for the 3R-CaGe2 and a/b=3.999(2) Å, c=30.714(3) Å and V= 425.52(5) Å 3 for the 6R-CaGe2, in line with the literature. [12,19,20,24] Likewise CaSi2 the CaGe2 presents a turbostratic disorder with a preferential orientation of the planes, impeding an adequate refinement. [20] The Raman spectra for CaGe2 (Figure 1-b), presented two A1g modes at 300 and 202 cm -1 and three Eg modes at 244, 235 and 125 cm -1 . In layered hexagonal materials such as the 3R-and 6R-CaGe2 the Eg modes correspond to the in-plane lattice vibrations while the A1g to the out-of-plane. [24] In certain occasions some modes can be activated depending on the polarization of the incident light while some others are independent of this variable. The SEM pictures for the CaGe2 showed in Figure 1-c indicate a layered morphology, with particles of different lateral size, agglomerates of several stacked layers and some particles with different morphology.

• Germanane The germanane was obtained from the CaGe2, by dissolution in concentrated HCl at -20°C, according to Equation 2. Contrary to siloxene, [25] the formation of germanane does not undergo a hydrolysis reaction even at temperatures >0°C, yet the low temperatures increase the crystallinity. [12] Consequently germanane mainly forms Ge-H bonds and no Ge-OH, following the formula Ge6H6, which contrary to polysilane (Si6H6) is stable 10 µm 10 µm c) in air. [START_REF] Brandt | Silicon Chemistry: From the Atom to Extended Systems[END_REF] The resulting powder is reddish and exhibits photoluminescence in the infrared. [12] 3CaGe2 + 6HCl + 3H2O → Ge6H6+ 3CaCl2+3H2(g)

(2)

The preferential bonding of Ge-H over Ge-OH reveals the different oxidation behavior of Si and Ge sheets. This difference can be understood in terms of the binding energies, the Si-O bond (8.0 eV) is significantly stronger than the Ge-O (6.6 eV) and the Si-H bond (3.0 eV) is slightly weaker than the Ge-H bond (3.2 eV). The absence of -OH bonds improves the germanane stability. [26] Nevertheless, the prolonged exposure to moisture causes substitution of Ge-H bonds by Ge-OH, forming the Germoxene Ge6OH3H3. This compound has much less structural stability and the introduction of -OH groups predominately influences the band gap. [11,[START_REF] Brandt | Silicon Chemistry: From the Atom to Extended Systems[END_REF] Figure 2-a reveals the preservation of the layered morphology after the topotactic deintercalation of Ca in CaGe2. The particle size distribution is inhomogeneous, various lateral sizes and stacks of different layers are observed. Indeed, the TEM images show the presence of several staggered layers as well as holes on the particle surface, probably caused by the H2 released during the synthesis process.

The XRD pattern for germanane (Figure 2-c) is in line with the reports in the ICSD database (192507) for (GeH)n. The broad diffraction peaks indicate a decrease in the crystallite size. The Le Bail profile matching shows the presence of two polymorphs, 3R-GeH and 6R-GeH, thus the crystal symmetry of CaGe2 has been preserved after Ca deintercalation. The refined cell parameters of the 3R polymorph are a/b=3.922(4)Å, c=11.8764(7)Å and V=158.2(9)Å 3 , and for the 6R a/b= 4.027(9) Å, c=34.6(1)Å and V=486.9(3) Å 3 (Figure S2). Similarly to CaGe2, the germanane presents an inherent turbostratic disorder that limits the quality of the refinement, although the obtained cell parameters are in line with the literature. [11,12,27] The c lattice constant expands from 10.320(7) Å in 3R-CaGe2 to 11.8764(7) Å in 3R-GeH and from 30.714(3) Å in 6R-CaGe2 to 34.6(1)Å in 6R-GeH. The a cell parameter experiences a slight decrease from 4.008(2) Å in CaGe2 to 3.922(4) Å in germanane for the 3R polymorph, while for the 6R there is a slight increase from 3.999(2) Å in CaGe2 to 4.027(9) Å in germanane, in agreement with the literature. [11,16,21] The expansion in the c parameter from CaGe2 to germanane, is caused by the replacement of Ca 2+ by two -H between each layer. [16] The interlayer distance d, calculated from the Bragg Equation, is 6.14 Å which is slightly lower than the one of siloxene 6.31 Å. [25] This decrease is related with the preferential bonding of germanane with -H and the almost absent -OH groups. [11,12] The electron diffraction (Figure 2-d) for germanane presents a high crystallinity and contrary to siloxene, [25] it is stable with the electron beam, thus the experiment can be performed under normal conditions. The pattern shows a preferential orientation of the planes and can be indexed in a hexagonal cell assuming a [011] zone axis. Several polymorphs are reported for germanane: the 1T (P-3m1one layer per trigonal unit cell), 2H (P63mc-two layers per hexagonal cell), 3R (R-3m three layers per rhombohedral cell), 4H (P-3m1 four layers per hexagonal cell) and 6R (R-3m six layers per rhombohedral cell). They all present a similar value for the a cell parameter, while the c varies according to the number of layers per unit cell. [11,21] Each polymorph present its stacking sequence, the 3R has ABC, the 4H A'ABC and the 6R A'AB'BC'C. [19] In analogy with CaGe2 the interlayer distance is directly related to the staking sequence in the polymorph, the larger the distance is the highest is the reactivity. [11,19,27] Finally, several polymorphs can coexist in the same sample, thus in some cases their identification can be complex. [19] The Raman spectrum (Figure 3-a) shows a change with respect to the CaGe2, and it is composed of only one band centered at 302 cm -1 corresponding to the in-plane E2 mode of the Ge-Ge bond. This signal is blue-shifted compared to the E2 Ge-Ge signal for c-Ge centered at 297 cm -1 . [16] A similar band is observed in CaGe2, corresponding to an out-of-plane A1g vibration at 300 cm -1 . These results are in line with the literature, although the A1 mode should be present at 227 cm -1 , probably the polarization of the incident light deactivates this Raman mode in our germanane. The Infrared spectrum in Figure 3-b, shows the presence of Ge-H vibrations, centered at 2000 cm -1 (Ge-H stretching) and 570 and 507 cm -1 (Ge-H wagging) preferentially oriented parallel to the c axis. [12] Other weak vibration modes are found at 770 and 850 cm -1 , assigned to the bending of Ge-H2, probably located at the edges of the layers or originated from Ge vacancies. [16,26] The band at 830 cm -1 corresponds to the Ge-O-Ge stretching mode, indicating a partial oxidation of the planes or the presence of glassy/amorphous oxides. No -OH vibrations are found for germanane, thus the bonding is preferentially done with -H.

In order to evaluate the stability of germanane, an in situ controlled-temperature XRD was performed from 30 to 450°C (Figure 4). The (002) and (100) Bragg reflections of germanane are present until 150°C, temperature after which they shift towards higher angles and intensity decreases until complete disappearance at ~300°C. Meanwhile, the peak at 27° assigned to c-Ge produced as a synthesis by-product and the additional small peaks from the Kapton window remain unchanged.

According to the literature, the amorphization of germanane starts at 75°C and is completed at 175°C. The dehydrogenation occurs between 200-250°C and at 300-350°C the residual Cl from the synthesis is desorbed. Due to a stronger Si-H bonding compared with Ge-H, the dehydrogenation temperature for germanane is lower than the one of siloxene (400°C). [12,16,28] The thermal stability of germanane can be improved by replacing the Ge-H bonds by the less reactive Ge-CH3 ones. [15] The electrochemical behavior of germanane was evaluated by galvanostatic cycling in Li, Na and K half-cells. The electrolyte was 1 M LiFP6 (NaPF6) in 1:1 EC/DMC + 1% FEC, while 0.8 M KPF6 (KFSI) in 1:1 EC/DEC were used for potassium. Figure 5 shows the galvanostatic curves and their respective derivative curves. The discharge capacities for the first cycle are 3732, 982 and 485 mAh/g and for the second one 2150, 495 and 205 mAh/g for Li, Na and K, respectively. Note that the conductive additive contributes to the capacity with ~270 mAh/g for Li, ~120 mAh/g for Na and ~150 mAh/g for K (Figure S3). Surprisingly, the sodiation of germanane delivered a capacity that exceeds the theoretical capacity for NaGe (396 mAh/g), according to the literature more than one Na can be inserted in the Ge matrix. [29,30] For potassium, the optimal cycling conditions must be established before assuming an improved cyclability. The galvanostatic cycling of germanane takes place at higher voltages compared to siloxene. [25] The first discharge for Li and Na is characterized by a plateau at ≈1.5 V and 1.3 V, respectively, assigned to the reduction of the FEC additive. Following, for Li there are two regions with different sloping profiles, the first one at around 0.6-0.3 V and the second one from 0.3-0 V. For the first charge and subsequent ones, two pseudo-plateaus are observed from 0.3-0.5 V and 0.5-1.0 V. The second discharge is slightly different from the first one, and a plateau is observed at 0.65 V, followed by a region with a sloping profile prolonged until 0.15 V. These features are reflected in the derivative curve (Figure 5-b) by a three reduction peaks at 1.2, 0.5 and 0.14 V during the first discharge, while the second one presented reduction peaks at 0.65 (plateau in the galvanostatic curve), 0.32 and 0.16 V. For the first and second oxidation, peaks at 0.4 and 0.95 V are observed, in line with the two-pseudo plateaus in the galvanostatic curve.

For sodium, in the first discharge after the plateau at 1.3 V, the potential decreases with a constant slope. For the first charge and subsequent ones, a pseudo-plateau is observed between 0.5-0.7 V, which gradually disappears as the cycling proceeds.

The second discharge presents a constant sloping profile until 0.2 V followed by a steady decrease in the potential. All these processes are displayed in the derivative curve (Figure 5-d), in the first discharge by reduction peaks at 1.3 and 0.04 V, accompanied by two other small signal at 0.6 and 0.7 V. For the first charge, one oxidation peak is observed at 0.7 V, in line with the pseudo-plateau in the galvanostatic curve. The second cycle, presents a double reduction peak at 0.08 and 0.04 V with a shoulder at 0.2 V, and an oxidation peak at 0.7 V with a shoulder at 0.4 V. For potassium, the first discharge shows a very prolonged plateau at ≈1.0 V, followed by a gradual decrease in the voltage.

Since this system has no FEC in the electrolyte formulation, this plateau must be attributed to another phenomenon than the reduction of FEC. The first and subsequent charge steps present a small region with a different slope approximately from 0.45-0.55 V that gradually vanishes with the cycling. The second discharge has a constant decrease in the voltage. The derivative curve (Figure 5-f) showed a reduction peak at 1.0 V, in line with the plateau in the galvanostatic curve, and two other peaks at 0.1 and 0.018 V during the first discharge. For the second discharge two reduction peaks are observed at 0.31 and 0.01 V.

The first and second charge presents only one oxidation peak at 0.5 V.

The observed phenomena for the lithiation of germanane are in line with the only report available in the literature. [17] The galvanostatic curve presents a sloping profile. The derivative curve displays a broad reduction peak at 0.3 V and two oxidation ones at 0.5 and 0.9 V. Given the lack of information regarding the electrochemical mechanism of germanane, the source of these peaks remains unclear. The reported reversible capacities for germanane are in the range of 1108 mAh/g while for this work 2000 mAh/g were obtained at the same rate. [17] Regarding the capacity retention properties (Figure 6), the germanane still delivers 1500, 354 and 150 mAh/g for Li, Na and K after 30, 35 and 30 cycles corresponding to a capacity retention of 67, 71 and 73%, respectively. Note that the capacity retention percentages are referred to the second cycle. The germanane showed great cyclability at high C/rates for Li as observed in Figure 6-b, where capacities in the range of 1100, 1000 and 900 mAh/g were delivered at C, 2C and 5C, respectively. This excellent rate capability can be attributed to the higher electron mobility in germanane compared to bulk Ge. [26] The sodiation of germanane is less accessible at high C/rates and 220, 170 and 120 mAh/g are obtained at C, 2C and 5C, respectively. At these rates, probably the capacity mainly comes from a capacitive behavior, as the Na ions do not have sufficient time to access the bulk of the layers, or from the conductive additive (120 mAh/g). Based on this information, the electrochemical behavior of germanane vs Li at high C/rates was tested, the results are presented in Figure 7. As observed in Figure 7-a and Figure 7-b, the profile of the galvanostatic curve for germanane cycled at C and 2C resembles to the one at C/10 described above, no significant changes, as polarization, are observed except for a size reduction of the plateau at 0.6 V during the second discharge for C and 2C. The capacities for the first discharge were 2525 and 2383 mAh/g and for the second one 1560 and 1523 mAh/g for C and 2C, respectively. A priori there is no major decrease in the capacity for C and 2C during the first cycles. For instance, after 25 cycles 1130 mAh/g are delivered at 1C and 2C, corresponding to a capacity retention (with respect to the second cycle) of 72 and 74%, respectively. For the cell at 2C after 58 cycles 990 mAh/g are obtained with a capacity retention of 65%. These values are higher compared to the reports in the literature, 530 and 265 mAh/g for 1C and 2C. [17] Thus, the germanane is very promising for high rate applications, for comparison siloxene presents a capacity retention of 52% after 58 cycles at 2C. This improvement in germanane could be related with the almost 400 faster Li ion diffusion [5] and 2 orders of magnitude higher electronic conductivity [START_REF] Jung | [END_REF] of Ge compared with Si.

The electrochemical behavior of bulk Ge and germanane were compared (Figure S4). In bulk Ge for the first discharge there is one plateau at 0.45 V, a pseudo plateau at about 0.2 V, reflected in the derivative curve by two reduction peaks at 0.43 and 0.14 V with a shoulder at 0.3 V. For the first and subsequent charge, there are two regions with a different slope between 0.3-0.5 V and 0.5-1.0 V, this last one gradually disappears with the cycling; only one oxidation peak is observed in the derivative curve at 0.43 V, accompanied by a shoulder for the second charge. The second discharge presents a plateau at 0.50 V and for the subsequent discharges the plateau appears at a higher potential 0.6 V. The derivative curve showed two reduction peaks at 0.48 and 0.14 V with a shoulder at 0.3 V. It is possible to observe then certain differences in the electrochemical behavior of germanane and bulk Ge; for the first discharge the germanane does not present the plateau and the reduction peak at 0.45 V, neither the shoulder at 0.3 V observed for bulk-Ge, while the peak at 0.14 V is present in both. For the charge, both materials share the oxidation peak at 0.43 V (region with different slope in the galvanostatic curve) and germanane presents an extra oxidation peak at 0.94 V (second pseudo plateau in the galvanostatic curve). These features are slight indicators of a different lithiation process, since the Ge is very sensitive to the cycling conditions. Probably due to the layered character of germanane the lithiated intermediates or even the electrochemical mechanism might be different. The germanane presented higher capacity values compared to bulk Ge, for both Li and Na (Figure S5). As expected the germanium presents an excellent capacity retention, property that is transferred to the germanane. This property along with the high reversible capacity renders germanane an excellent choice as anode material for Liand Na-ion batteries. Finally, the potassiation of germanane was evaluated (Figure S6), initially the same electrolyte formulation as for Li and Na was tested, 1 M KPF6 in EC/DMC 1%FEC and 1 M KFSI in EC/DMC 1%FEC. The delivered capacities were 300 and 550 mAh/g for the formulation with KPF6 and KFSI, respectively during the first discharge. The subsequent cycles are characterized by a remarked capacity loss and by the 5th cycle <50 mAh/g are obtained. Concerning the profile of the galvanostatic curve, in both cases a plateau at ~1.5 V is observed for the first discharge followed by a gradual decrease in the voltage until the end of discharge. The subsequent charge/discharge present an abrupt change in the voltage that is more pronounced as the cycling proceeds. Consequently, the germanane does not cycle correctly with K under these conditions. Therefore alternative electrolyte formulations were proposed, 0.8 M KPF6 in 1:1 EC/DEC and 0.8 M KFSI in 1:1 EC/DEC (Figure S7). The obtained capacities for the first discharge were 922 and 485 mAh/g for KPF6 and KFSI, while the second discharge delivered respectively 202 and 205 mAh/g. For KPF6 EC/DEC, the galvanostatic curve presents a sloping profile during the discharge/charge cycles. For KFSI EC/DEC a plateau at 1.0 V is observed during the first discharge and the subsequent charge/discharge cycles present a sloping profile. The cells cycled with KPF6 EC/DEC presented more irreversibility and capacity fading compared to KFSI; and after 33 cycles only 56 mAh/g are delivered for KPF6 in contrast to 150 mAh/g for KFSI. Therefore, as observed for siloxene, the formulation KFSI in EC/DEC exhibits the best performance in terms of reversible capacity and capacity retention, though tests in full cell configuration are necessary to assess the real performance of germanane in KIB. Finally, in order to get more information on the electrochemical kinetics, cyclic voltammetry has been performed on germanane. Figure 8-a, shows the CV curves for the first cycles of germanane, during the first cycle one reduction peak at 0.94 V and two oxidation ones at 0.47 and 1.06 V are observed. For the second cycle, there are three reduction peak at 0.55, 0.3 and 0.04 V while for oxidation two peaks at 0.45 and 1.1 V. The profile of the CV curve, evolves after the second cycle and a reduction peak at 0.32 V appears and the peak at 0.04 V is more defined and shifts to 0.08 V as the cycling proceeds. Meanwhile the oxidation peak gradually shifts to 0.43 V while the peak at approximately 1 V decreases in intensity. These processes are in line with the galvanostatic curve, in which two pseudoplateaus are found upon discharge and charge. In general the profile of the CV curve for germanane suggests a good stability and reversibility for the system. Figure 8-b,c show the CV curves at different scan rates from 0.1 to 100 mV/s. For scan rates between 0.1 and 1 mV/s the CV curve displays the previously mentioned peaks, which become broader and less defined and the peak current increases with the scan rate. For scan rates from 10 to 100 mV/s, the peaks are very broad and the peak current continues to augment, indicating a high polarization.

The presence of capacitive or diffusion controlled processes was calculated from the relationship between the peak current (ip) and the scan rate (v): [31] i= av b (1) Where b is determined by the slope between log(ip) vs log(v) as in Figure 8-d. A b value of 0.5 indicates a diffusion controlled process while b=1 represents a capacitive process. The b value obtained for germanane is 0.59 for both 0.1 to 1 mV/s and 5 to 100 mV/s. This value indicates that the storage mechanism is mainly diffusion controlled, in which the Faradic reaction occurs in the bulk of the material, with a smaller contribution from capacitive mechanism in which the storage only takes place at the surface of the layers and not in the bulk. [31] As observed the electrochemical properties of germanane compared to bulk Ge for different alkali ions slightly differ, clearly the layered morphology and the conditions for cycling might be involved. First, the layered morphology buffers the volume variations, reducing the strain due to reaction with alkali.

Likewise, it provides faster diffusion paths for the alkali ions, allowing high rate applications. Secondly, recent studies indicate that Ge is particularly sensitive to the cycling conditions and parameters such as C/rate, morphology or electrode formulation can influence the type of phases that are formed. For instance in one of our previous studies for the lithiation of Ge, it was found that the cycling at relatively slow regime permits the stabilization of Li17Ge4, a more lithiated phase than Li15Ge4. [32] Another study concerning the sodiation of Ge Nanowires, has shown the formation of Na1.6Ge, much sodiated phase than the expected NaGe. [2] These results put in evidence the influence of the different parameters involved in the cycling with the reversible capacities of Ge-based materials, the phases that are formed often differ from those ones commonly known, thus deeper studies are needed. In the case of germanane, the layered morphology not only buffers the volume changes but also allows to attain much higher reversible capacities compared to bulk Ge.

Conclusions

In summary, the germanium-based layered phase, the germanane, was obtained from the layered CaGe2. After topotactic deintercalation of Ca 2+ , the CaGe2 transfers the same crystal symmetry to the germanane and two polymorphs were identified by XRD, the 3R (R-3m, 3 layers per rhombohedral unit cell) and 6R (R-3m, 6 layers per rhombohedral unit cell). The SEM and TEM analysis showed a layered morphology for both CaGe2 and germanane. The Raman and infrared characterization indicate a preferential bonding of Ge with -H and almost no formation of Ge-OH. The presence of Ge-O-Ge bonds was identified and ascribed to a possible oxygen incorporation in the Ge planes or the formation of amorphous GeOx as by-product of the reaction. The thermal stability of germanane was estimated to ≈250°C, yet the amorphization starts at lower temperatures. The electrochemical performance of germanane was evaluated in Li, Na and K half-cells. The reversible lithiation capacities are in between 1700-2000 mAh/g while the sodiation between 400-500 mAh/g. These results are very promising and higher compared to bulk-Ge cycled under the same conditions. Particularly, the sodiation is higher compared to siloxene, [25] proving the feasibility of Na insertion into layered group 14-derivated phases. The germanane displayed good performance at high rates and at 1C and 2C capacities in the range of 1100-1200 mAh/g are obtained, values that are superior to the previous reports in the literature. [17] For the potassiation, the results are more ambiguous, the germanane seems to deliver good reversible capacities when the KFSI EC/DEC formulation is used, yet, tests in full cell configuration are necessary.

Finally, the layered morphology of germanane influences the electrochemical behavior by buffering or mitigating the volume expansion during cycling. The decrease in the irreversible capacity, remains a challenge, and understanding of the role of the -H groups in the first discharge and formation of the SEI layer is crucial at this stage. Additionally, due to its structure the lithiated/sodiation intermediates might be different and even another electrochemical mechanism could take place. For instance, the theoretical studies predict the absorption of Li and Na in the germanane layers with lower Li diffusion barriers (0.21-0.76 eV) than in siloxene (1.2 eV). [33,34] This work opens the quest for developing all the potential from the germanane as anode for LIB, NIB and KIB.

Experimental Section

Synthesis: The CaGe2 Zintl phase was mechanically synthesized by placing stoichiometric amounts of Ca (99% ACROS Organics) and Ge (325-Mesh, 99%, ACROS Organics) in an airtight 50 mL WC jar, with a ball:mass ratio of 10:1. The jar was rotated at 600 rpm for 18h, in a planetary ball mill (RETSCH PM 100). The recovered powder was loaded into stainless steel tubes sealed by Arc welding under Ar atmosphere and annealed for 50 h at 800°C. The germanene was synthesized in air atmosphere, by dissolving ~300 mg of CaGe2 in ~30 mL of HCl (35% VWR Chemicals) at -20°C for 8 hours. The reddish product was washed with distilled water and acetone, separated by centrifugation and vacuum dried for 30 min. All synthesis products were kept in an argon atmosphere to avoid further oxidation. Note that this synthesis method has been adapted from [17] , though in this work the ball milling of CaGe2 prior the annealing process, clearly results in the absence of impurities such as CaO in CaGe2 and in less residual c-Ge in germanane.

The Powder XRD patterns were recorded in a Bruker D8 Advanced diffractometer with Cu radiation (λ1 = 1.54056 Å, λ2 = 1.54439 Å), using an in situ cell with Be window described in ref [35] . The germanane diffractograms were collected with a zero background single Si crystal XRD sample holder. The diffraction patterns were refined using the Fullprof software. Confocal ex situ Raman Spectroscopy was performed using a DXR 2 Raman Microscope (Thermo-Fisher Scientific, 532-nm excitation). The samples were placed in a glass slide and sealed with Kapton tape in order to avoid exposure to air. The Fourier transformed Infrared Spectra (Nicolet IS10, Themo-Fisher Scientific) were performed using KBr methods, an airtight cell with NaCl window was used for air sensitive samples. Particle morphology, size and microstructure were studied by SEM (SEM-environmental FEI Quanta 200 FEG microscope) while the composition was determined by Energy Dispersive X-ray EDX (X INCA Oxford). TEM was performed in a TEM-FEI Tecnai F20 S-TWIN, operating at 200 kV fitted with a Gatan Image Filter Tridiem in post column. The electron diffraction patterns were obtained with Selected Area Electron Diffraction (SAED). The air sensitive samples were prepared in an Ar filled glove box and transferred to the TEM under an Ar flow.

In situ temperature-controlled XRD. The XRD with temperature were performed in a Bruker D8 Advanced diffractometer with Cu radiation (λ1 = 1.54056 Å, λ2 = 1.54439 Å) equipped with a HTK 1200°C Anton Parr Chamber. Electrode preparation. The electrodes were prepared with a 1:1:1 mass ratio of active material, carbon super C45 and Carboxyl Methyl Cellulose (CMC-DS = 0.9, Mw = 700 000 Aldrich), dissolved in distilled water with 0.1% of Triton X dispersant. The slurry was casted into copper foil using a doctor blade (50 µm thickness) and dried at ambient conditions for one day. 11.1 mm disks were cut and dried under vacuum at 70°C overnight.

Electrochemistry. The electrodes were tested in Li, Na and K half-cells using CR2032 coin cells, 1 M LiPF6 (NaPF6) in Ethylene Carbonate (EC)/Dimethyl Carbonate (DMC) [1:1] electrolyte with 1% Fluoro-ethylene carbonate (FEC) as additive, and a Whatman glass fiber separator (GF/ D, 675 μm). For K several electrolyte formulations and the impact of FEC addition were tested, 0.8 M KFSI in 1:1 EC/DEC, 0.8 M KFSI 1:1 EC/DMC, 0.8 M KPF6 1:1 EC/DEC and 0.8 M KPF6 1:1 EC/DMC. Galvanostatic cycling was performed at 25°C between 0 and 2 V versus Li/Li + , Na/Na + or K/K + at C/20 or C/10 (C/n = 1Li, Na or K/n h), using a VMP3 or MPG2 (Biologic) device.

Figure 1 .

 1 Figure 1. a) Le Bail profile matching for the CaGe2 phase, b) Raman spectrum for CaGe2, c) SEM pictures of the CaGe2 .

Figure 2 .Figure 3

 23 Figure 2. a) TEM picture of germanane, b) XRD diffraction pattern and c) Electron diffraction pattern for germanane

Figure 4 .Figure 5 .

 45 Figure 4. In situ XRD with temperature from 30-450°C for germanane

Figure 6 .

 6 Figure 6. Capacity retention of germanane vs a) Li at C/10, b) Na and c) K at C/20. Rate performance at different C/rates for germanane vs d) Li and e) Na. The capacity values correspond to discharge capacity .

Figure 7 .

 7 Figure 7. Galvanostatic and their corresponding capacity retention curves for germanane cycled vs Li at the rate of a), c) 1C and b), d) 2C.

Figure 8 .

 8 Figure 8. a) Cyclic voltammetry of germanane from first to sixth cycle at a scan rate of 0.1 mV/s. b) Cycling voltammetry at different scan rates from 0.1 mV/s to 1 mV/s. c) Cycling voltammetry at various scan rates from 5 mV/s to 100 mV/s. d) Determination of b-value using the relationship between the peak current and the scan rate

Entry for the Table of Contents

Towards germanium layered materials as superior negatives electrodes for Li-, Na-, and K-ion batteries

GeH n


Anouk Cohen
email: anouk.cohen@wanadoo.fr

John Angell

The Distribution of Knowledge and the Material Presence of Books: The Sidewalk Book Vendors of Rabat and Casablanca, Morocco

Keywords: Sidewalk book vendors, Books, Distribution of knowledge, Literacy, Morocco

Many of the books, newspapers, and magazines sold in Rabat and Casablanca are distributed directly by informal vendors in kiosks, on sidewalks, and in small bookshops. The growing number of kiosquiers, terrassiers, and bouquinistes (as they are called locally) suggests that they are not as marginal as their appearance might suggest. This article discusses the critical role of street traders in these two Moroccan cities, many either semi-literate or non-literate, in the circulation of the printed word-and of knowledge.

The broad avenues that separate the medinas or old cities of Morocco's administrative and economic capitals, Rabat and Casablanca, from surrounding newer zones might seem like unexpected locations to sell books. Displayed on sheets of cardboard along the sidewalks, every possible kind of book can be opened, perused, or purchased, ranging from the Qur'an and other religious tomes to novels, novellas, essays, and technical manuals. Although some formal bookstores exist, numerous "sidewalk bookstores" [START_REF] Yves | Les Gens du livre[END_REF][START_REF] Yves | Les Gens du livre[END_REF]; [START_REF] Soraya | Les Réseaux du livre islamique. Parcours parisiens[END_REF], often as close as twenty meters apart along urban avenues, transform urban sidewalks into thriving commercial zones. On heavily trafficked downtown intersections, this vast colorful mosaic of printed matter adds visual and intellectual zest to public life.

This profusion of print material inspires two immediate observations: First, literacy artifacts of every description dominate these urban streets and public spaces; second, the print trade involves a multitude of vendors operating a great diversity of sales locations. Their spaces vary from specialized booksellers in shops enclosed behind shop fronts and equipped with doors to buralistes, 1 small installations, also equipped with doors, selling an array of items including newspapers, magazines, and books as well as cigarettes and other small consumer goods, kiosquiers offering press publications and books from open booths overflowing into the streets, and "terrassiers" whose displays of books, newspapers, and magazines are spread out at the level of the sidewalk. In addition, there are bouquinistes, generally located in souks and medinas, selling books and used journals from ten square-meter, U-shaped boutiques, sometimes from behind a wooden counter. In reality, there are two categories of street businesses selling printed materials-those that operate along the streets and in the market squares, such as kiosquiers, terrassiers, and bouquinistes, and those who possess enclosed spaces, such as buralistes (or tobacco shops) and formal bookstores.

The present study focuses primarily on the first category of informal urban vendors of printed matter. Despite their ramshackle appearances, the large number of terrassiers, kiosquiers, and bouquinistes indicates their vital role in the distribution of print and knowledge. Located in otherwise lightly trafficked sites on corners of major streets such as Mohammed V and Hassan II Boulevards, in proximity to the railway station, the post office, and numerous business establishments, these easily accessible vendors regularly attract large crowds during busy times of day. The goal of this article is to present my findings about these vendors' crucial role in the circulation of the printed word-and therefore of knowledge-in Rabat and Casablanca.

To understand their day-to-day functioning, I inquired about who the vendors are, how they work, and their relationships with the printed word, particularly books. My first objective was to understand the trajectories of terrassiers, kiosquiers, and bouquinistes, which then led me to examine their work practices and professional skills more closely, as well as details about their operations such as locations, hours, prices, and physical layouts, and finally the reasoning behind their approaches to displaying and classifying their merchandise, as well the atmosphere of their environs. In the process of conducting my study, my focus expanded beyond street vendors to include the people with whom they interacted, including other book vendors, publishers, and customers. I also developed a specific interest in the ways in which kiosquiers, terrassiers, and bouquinistes, who are often semi-or non-literate, enable populations that have limited familiarity with print and modest financial resources to gain access to written language, thereby helping disseminate the ideas of censored authors, conducting businesses organized around the physical presence of books and other printed materials.

Trajectories

Vendors, Customers, Spaces

As elsewhere in Morocco and other Arabic countries, most publications in Rabat and Casablanca, particularly newspapers and magazines, are directly distributed on the street, on sidewalks, or in kiosks. Terrassiers, more modest locations consisting of a few sheets of cardboard on the ground (See photo 1), are often in close proximity to their peers. While kiosquiers and terrassiers serve primarily lower-income readers who tend to purchase press more than books and whose familiarity with the printed word may be modest, bookstores and buralistes target more serious readers who are able to spend up to 120 MAD [approximately 110 euros] for books imported from the Middle East and 250 MAD [approximately 203 euros] for books from France on specific, often professional topics. Many of these customers are teachers, journalists, lawyers, and doctors who tend to purchase books only from sales outlets concentrating on their preferred language-either Arabic or French. 3 Bookstores that specialize in Arabic books typically offer imports from Lebanon or Egypt. The clients of French-language bookshops are literate in French and derive social status from owning imported French books that can cost more than the vast majority of Casaouis and Rabatis can afford. 4 This binary market is mirrored in the physical locations of publishing houses and bookstores, which are located in specific neighborhoods depending on language. In both Rabat and Casablanca, businesses involved in the production and distribution of Arabiclanguage books tend to be located in the Habous districts where in addition to books, wholesale goods, from clothing and cooking utensils to fruits and vegetables, are also available. The French-language book trade is primarily concentrated in the central district of Casablanca and the Maârif neighborhood, where other businesses that belong to the old city's culture are located, including cafés (Café de Paris), restaurants (le Petit Poucet, formerly frequented by Jean Genet), and bookstores (the Livre-Service, the Librairie de France, the Librairie Farraire, the Librairie des Sciences, etc.).

Over time, kiosquiers and terrassiers have gradually moved into the same area as these businesses. The presence of foreign populations, mostly French and Spanish, in this district has been an important factor in their development, and they represent an excellent niche market for pioneering terrassiers, kiosquiers, and Retracing the Itinerary of the Book.

An ethnography

This article presents the results of an ethnographic study in Rabat and Casablanca that was conducted during 2006-2007, as well as return trips in 2008, 2009, 2010, and 2015. Over a period of nine years, I met and talked with a large number of terrassiers, kiosquiers, and bouquinistes. In parallel to these interviews, I was also able to observe practices surrounding books in the street for one and one half years. I decided to conduct this study of literacy artifacts and the social and economic relationships surrounding them in order to comprehend the full breadth of the diversity of the printed word. 2 Retracing the path of the book raised my awareness of the key role of street vendors and the ways in which their merchandise structures their work practices and gestures as they distribute books and as they contribute, each in their own ways, to the circulation of the written word. These reflections are an extension of Christian Jacob's exploration of the connections between the work of the hand and that of the mind in the second volume of Lieux de savoir series, where he sought to "reduce the hiatus between manual and intellectual practices, or more specifically, to contemplate the connections between them" [Jacob, 2011: 20].

bouquinistes dealing in foreign-language books, newspapers, magazines, and graphic novels. The presence of printed materials ultimately defined this district, an influence that continues to this day. Instead of traces of the colonial and urban past, their presence reflects the close relationship between their locations and the goods that they sell: These merchants "make place"in Christian Jacob's words [2007: 17]-through their boutiques, kiosques, and terrasses.

"J'ai toujours fait ça!" [This is what I've always done!]

Most street vendors became booksellers as a legacy from a father or uncle who transmitted the boutique and trade knowledge to a son or nephew who then learned the trade by imitating their elders' actions. The trade is almost exclusively transmitted among male family members from generation to generation. Although women are rarely involved in selling books in kiosks and sidewalk stands, many owners' daughters, sisters, or nieces of work in bookstores, where the men place orders and greet publishers and authors while women greet customers, provide information, and manage book sales. This heritage partially explains why vendors are generally not particularly attached to books-they often work "in the book" because they have "always done this!" or because "there's no [other] work."

Ali is a bouquiniste at Derb Ghellaf, a vast market known for electronics-cellular telephones, computers, software, DVDs, televisions, portable MP3 players-as well as a wide variety of other goods ranging from clothing, lingerie, linens, and dishware to fruits, vegetables, and used books. For Ali, it is "better to work in the book trade than sell vegetables-that's no way to make a living!" He also finds selling books in the souk an agreeable way to make a living. He particularly appreciates the Derb Ghellaf market because of the work environment and above all the concentration of such a wide diversity of small businesses. For example, he can easily leave a colleague in charge of his stall if he needs to run errands. Another reason Ali is especially fond of the work environment is that the merchandise is well organized. Although Ali professes a certain detachment from the literary content of his wares, Larbi, who operates the stall adjacent to Ali's, is a regular reader for whom the link between his profession and his passion for books is direct.

Many bouquinistes, kiosquiers and terrassiers are semior non-literate, but others, like Larbi and Hassan, a well-known kiosquier on the Avenue of the far in Casablanca, are widely-read and are often consulted by faithful customers about the most recent books. Hakim, who lives near Hassan's kiosk, stops by every week to discuss what "books to read." "Before I met Hassan, I never read. At home, nobody did. And then, with Hassan and other customers, we talked about current events, the newspaper headlines, and we met there and discussed. Hassan introduced me to books published in Egypt and Lebanon. So that made me want to read." It became clear to me that the relationships between each kiosquier, terrassier, and bouquiniste and his customers was unique.

Becoming a Bouquiniste due to Opportunism

Seemingly random circumstances can influence a book vendor's choice of profession. Larbi is about sixty years old and earned the title hajj 5 after opening his shop in 1958. When I asked him what caused him to choose this profession, he answered: You know, in '54, they expelled me from school because I didn't want to read the schoolbooks. I didn't want to learn, so I read graphic novels. That was all I did! The principal summoned my parents and me and told me to leave school. So I started selling graphic novels to French, Spanish, Jewish, Italian people in the Maârif district. At first, I sold books in the rue du Jura, but then I opened a shop in the Derb Ghallef Souk. When the French left, a lot of them sold and sometimes gave their books to me.

A large number of foreign residents left Morocco in the 1970s after Moroccanization regulations on foreign and national capital were imposed that were intended to enable the country's oligarchs to become partners in foreign industrial and commercial firms, many of which were French. The new law required foreign investors to hire Moroccan co-managers for their companies, and some foreign investors who refused to accept these conditions sold or gave away their property and left the country. Larbi does not recall why some departing French nationals sold or gave him their books instead of to other vendors. Moroccans who became bouquinistes at the time often managed to acquire the libraries of departing French Photo 2 -Larbi, bouquiniste in Derb Ghellaf market (author photo, April 14, 2007).

nationals who were seeking to reduce the cost associated with shipping their possessions. This is why Larbi continues to exclusively sell French-language books, although, as he pointedly observes, he reads "only in Arabic." The Arabic music flowing from the radio in his shop contrasts with the older French books lining the bookcases in his shop, particularly J'ai Lu, Livres de poche, and Folio.

An additional reason for the prevalence of these series on Larbi's bookshelves is that he restocks from discounters reselling French books that originate in the pulp market in France and are shipped to Morocco. Discounters periodically organize sales on the Casablanca markets that are regularly attended by wholesale resellers from souks such as Derb Ghallef and Derb Omar. Bouquinistes purchase books wholesale for 5 to 10 Moroccan dirhams (MAD), reselling them for 15 to 30 MAD, depending on the series-Livres de poche and Pocket books cost 15 MAD, Folio and J'ai Lu cost 20 MAD, and J'ai Lu "rouge" [red] (part of a special "Aventure et passion" series) can cost as much as 30 MAD. Regardless of the series, recently published books are priced at 30 MAD. Larbi acquires books by adapting to the discounters' supply rather than pursuing a specific acquisition strategy. In fact, because of his shop is so small, Larbi's acquisitions are guided primarily by what is needed to maintain his inventory. Available space determines his visits to discounter markets, resulting in a seemingly random business plan-a competitor might have bought a particular book instead of him, or he might not have the shelf-space or resources to purchase what was on offer at a particular moment. Most importantly, the ability to purchase discounted books made it possible for Larbi to discover French literature.

Larbi is not limited to a single product line, however: A complicated series of events can always lead to a new commercial transaction, and professional trajectories are shaped by a need for balance between customer expectations and potentially less predictable opportunities. Bouquinistes are constantly searching for books, sometimes purchasing them from individuals, and they often asked me if I had books to sell. After discussing one of his favorite genres-eighteenth-and nineteenth-century Moroccan history books-Larbi confirmed that, "Books are expensive. Like encyclopedias." A small minority of his customers are collectors who are always looking for beautiful books and encyclopedias to enhance their personal libraries. I noted that a number of bookstore owners paid weekly calls to the Derb Ghallef bookstalls, usually on Sundays when their own stores were closed, to purchase books from older series, such as "J'ai lu rouge," that continue to be in demand. Although bookstore owners purchase books from kiosquiers and terrassiers, they also sell books that they are unable to sell to informal booksellers. I also observed customers who were probably unable to afford new books in a bookstore looking among the kiosks and sidewalk displays for specific works of French literature, usually for school. Many of these customers also report preferring the Derb Ghallef bouquinistes at because of their lending policies.

Censorship and Flexibility

Since the end of a long-standing ban on books written in Moroccan dialectal Arabic (Dârija) and Berber (Amazigh), the few books that are published can sometimes be found among kiosquier's or terrassier's displays. Before Amazigh was declared the second official language of Morocco in June 2011, following six months of popular uprisings, the authorities long enforced an Arabic-only policy. 6 Indeed, until quite recently, linguistic pluralism was stigmatized in most Arabic-speaking countries and particularly in North Africa, theoretically to encourage national unity as well as Pan-Arabism. Being multilingual was considered suspect, and minority language speakers were often accused of harboring unpatriotic values [Pouessel, 2008]. It is important to note that the ban on Dârija remains in effect [START_REF] Cohen Anouk | La langue du silence dans le Maroc urbain contemporain[END_REF]. Authors who distribute books written in Moroccan dialectal Arabic [as opposed to modern standard Arabic] report that nearly all bookstore owners resist carrying their books, but that some buralistes are willing to buy and display their books. It is also difficult to distribute books about sensitive subjects such as the King, sexuality, or the Western Sahara, 7 as well as books promoting critical or fundamentalist religious views. 8 In fact, Moroccan book vendors are tightly regulated, and the Ministry of Communication informs vendors which new acquisitions are likely to be banned. Street vendors are typically immune from these limitations and can sometimes sell books that lack official or publisher approval. Jamal, a bookstore owner at the Casablanca bookstore Livre service, noted that: When I import books I am required to have a visa from the Ministry of Communication, which can censor whatever they want. Before, censorship was more important than it is today. I have sometimes even been notified that particular books were banned directly from the division commissioner. I had to sign the statements and send them back, keeping a copy. At the time, we received at least thirty notices a year, but the last one that I received was in 2002, and there have not been anymore since then. Anything related to the person of the King or the Western Sahara is banned. For example, we weren't allowed to accept dictionaries that did not contain maps showing the [Western] For kiosquiers and terrassiers, official inspections usually focus on newspapers and magazines instead of books. Bookstore owners use their less formal colleagues to dispose of books that are banned after they have acquired them. In the end, kiosquiers and terrassiers serve as de facto purveyors of censored material, although not without taking some modest precautions. Banned books are generally not displayed openly, for example, and when a customer requests them, street vendors extract it from a bag or, in the case of kiosquiers, a hidden corner of their modest stalls. Bookstore operators, terrassiers, kiosquiers, bouquinistes are fiercely competitive, but they also cooperate with each other. In reality, operating in the street, where the intense circulation and transactions frustrate official surveillance efforts, allows kiosquiers and terrassiers to engage in underground practices and distribute almost any type of printed material. Kiosks nevertheless follow certain norms and are required to renew an annual official "authorization," remaining subject to cancellation and confiscation of their merchandise at any time. Mohamed, for example, inherited his kiosque permit from his father and pays an annual fee of approximately 1,500 MAD.

By contrast with kiosquiers, the status of terrassiers is entirely informal. Unlike Mohamed, Hassan, pays no fees for his stretch of terrasse or sidewalk. He even claims that, "I'm actually the one who does a favor by selling the political parties' and the Kingdom's newspapers!" Because they have no official obligations towards the government, terrassiers enjoy considerably more freedom than their peers, and, as a consequence, are the principal purveyors censored literature. In Rabat and Casablanca and other cities, banned texts circulate primarily via the street. Like nineteenthcentury door-to-door salesmen in France who sustained popular literacy practices by being more familiar with popular tastes than formal booksellers [START_REF] Roger | Colportage et lecture populaire. Imprimés de large circulation en Europe[END_REF], Moroccan terrassiers and kiosquiers allow censored texts to circulate with relative freedom.

The Street as a Sales Location

A lending system employed by the Derb Ghallef bouquinistes in Casablanca and other souks near universities as well as by certain kiosquiers provides access to literacy for people of more modest means. This loan system, which is surely as old as the world's first street vendors, is simple: A book purchased at full price can be exchanged for a second book for a 2 MAD fee for a trade paperback, or for 5 MAD for a "J'ai lu rouge," the most sought-after collection. There is no official return date, and, as Larbi tells his customers, "When you finish reading it, just come back." Larbi keeps no records of the books that he lends or borrowing dates: "Things work out," as he says. The practice is particular helpful for lower-income young people who prefer to borrow rather than to own. This allows books to "pass" from hand to hand until they eventually return to the seller, who is a key agent in a system of transactions that remains outside of the formal economy.

Mohamed is a kiosquier known for lending books at the same price as bouquinistes. His kiosk is open from 7 a.m. to 9 p.m. every day of the week except Sunday, although he leaves his nephew to keep the stall in the afternoons. He emphasizes the fact that his "work starts at four in the morning" when the Sochepress trucksthe major Moroccan press distributor-deliver the day's newspapers, magazines, and books. Publishers and authors also stop by throughout the day to deliver books. Mohamed avoids accumulating an over-supply of books because "they don't sell as well as magazines and newspapers." He prefers to adjust to customer demand rather than purchasing books that are difficult to sell. One of Mohamed's strategies is to base book orders on what nearby kiosquiers and terrassiers are displaying. When he sees that particular books are frequently displayed, he buys them at the Derb Omar market or the Casablanca neighborhood of Habous so that he can stock them as well. The majority of kiosquiers' and terrassiers' sales are newspapers and magazines. They generally carry a few academic or religious books in their inventory mostly in Arabic, as well as smaller format, practical books such as cookbooks and health or medicinal plants manuals, how-to books, and current events. These are displayed along with copies of the Qur'an, which is commonly for sale in the street. Neither vendors nor the faithful perceive direct contact with the sidewalk to be an affront to the sacred character of the Qur'an.

Unlike in bookstores, prices charged for books by kiosquiers and terrassiers, whose customers are mostly low-income readers, do not exceed 30 or 40 MAD. Bookstore prices can be as high as 300 MAD, particularly for French imports. This explains why kiosquiers, terrassiers, bouquinistes sometimes sell photocopied books imported from France or the Middle East after binding them like the originals and respecting their formats and cover designs.

Street sales require only a modest investment and inventory and, although bookshops are physically separated from the street, kiosquiers and terrassiers are in open spaces that allow passers-by direct contact with books, newspapers, and magazines while they pursue their urban itineraries. Although the boundary between different categories of informal vendors can be difficult to establish, purchasing a book in a formal bookstore seems to involve more intentionality than buying one on the way home from work, perhaps on impulse, from a sidewalk kiosk. Like their merchandise, the locations and morphology of the kiosques and terrasses explains this difference. Newspapers and magazines attract customers who might also be attracted by carefully arranged, colorful, modestly priced books arrayed on the ground. This insight has increased publishers' attention to the external appearance of books in order to capture the low-income consumer market.

Expertise and Professional Creativity

The Demand for Color

According to Leila Chaouni, director of the Moroccan publishing firm Éditions Le Fennec, colorful covers attract customers and facilitate the work of street vendors, many of whom have rural backgrounds and are semi-literate: 9

In the beginning, I wanted to publish serious-looking books like Gallimard and only use white covers. But many people warned me, asking 'What do you think the kiosquiers' and terrassiers' base their business on?' Colors are their frame of reference-'Hand me the green one! That red one needs to show better-it's selling well!' You can't just switch to white! With few exceptions, every publisher in the region now adheres to this principle. Colorful interior illustrations correspond to cover patterns of relatively neutral inter-locking geometrical shapes that are interchangeable between different genres. In this way, publishers can create simple covers without being forced to hire layout artists for cover designs who digitally retouch or rework downloaded images or illustrations from fine art books. Upmarket publishers sometimes order "standard images" painted by professional artists, while others design covers displaying figurative illustrations derived from a book's contents. Until the mid-1990s, publishers simply embossed covers with author names and titles in Arabic calligraphy against pale yellow, green, or brown backgrounds, but more recently, they use a range of strategies to focus on books' appearance. Most book covers currently published in Morocco feature colored drawings that complement content and guide both vendors and customers, either by establishing a direct connection between the title and the illustrations orfor those who are not fully literate-by using colors as cues.

Every vendor has his own technique: Some use mnemonic techniques to select, display, and sell books according to format, binding, and materials, while others use author names, titles, or topics associated with a particular color. For example, the kiosquier Mohamed distinguish contemporary Islamic publications from classical religious books called mujallad (from the word jild or leather, now often replaced by leatherette) using bindings and the gilded parts of book covers. In this way, he is able to differentiate between books that are part of the Arabic literary, linguistic, and religious heritage and are called turâth (turâth meaning cultural legacy), the Qur'an, commentaries and exegeses, poetry, and literature.

The Physical Presence of the Book

Most of these kinds of books are clearly designed for mass distribution and are relatively inexpensive (between 30 and 100 MAD), although the printing is of high quality. With colorful cardboard covers and surfaces that are occasionally glittered, they are of medium format (17 x 24 cm) and are rarely longer than one hundred pages. Vendors differentiate between the covers of contemporary Islamic books, some of which have cardboard covers and called "kutub sulufan," and softcover books called "kutub war'qa" (from waraqa, the Arabic word for paper). Softcover books come in several types, including Kutub war'qa, which exist in several categories, from novels, stories, and essays to religious volumes (which are distinguishable by their covers). Unlike novels (riwâya), novellas, and short stories (qissa), whose first-edition covers feature colored drawings, the covers of kutub war'qa diel-dîn (which are related to religion) are more esthetically sober with embossed calligraphic script against uniform pastel beige, green, or brown backgrounds. The differences between these three categories of Islamic books-mujjalad, sulufan, and war'qa-are mirrored in their appearance, enabling vendors to easily sort and display them separately.

Mohamed organizes books according to topics using clues on their covers (drawings, photos, paintings), type of script (calligraphy or not), and material composition. Some cases are more obvious-if a cover carries images of salads, couscous, or tajines, he knows that it is a cookbook… Colorful, flexible covers are easily identifiable as essays or literature. Smaller formats with finer-grained covers indicate publication in Lebanon or Egypt, whereas Moroccan books have specific characteristics due to local production techniques, including their format (medium, or 17 x 24 cm for essays and small, 14 x 21 cm for novels and short stories). Moroccan books also rarely exceed one hundred-fifty to two hundred pages and are usually printed on 80 gsm [standard letter weight] paper (which is tax-exempt) with covers in 300 gsm paper that is soft, plasticized, and matte. After identifying books, Mohamed uses easily recognizable publishing company logos instead of subjects to categorize them.

Like kiosquiers and terrassiers, bouquinistes in the medinas and souks also use color and format to organize their wares. In Casablanca, they are clustered in a corner of the Derb Ghallef souk. Like other Moroccan markets, these stalls are arranged according to specialty. The area occupied by the bouquinistes, which is near the electricians and locksmiths, consists of nine stalls selling books and used journals that are open from 9 a.m. to 6:30 p.m., except for Fridays, the "day of prayer." Bouquinistes specialize not only in a particular domain, such as school textbooks, literary works, or journals, but also in a specific language. A few sell only used Arabic-language books, but most sell French-language books. Vendors are intimately aware of competitors' inventories and willingly refer customers to each other.

Like his colleagues, Abderrahmane's stall is a narrow, cluttered space with walls covered in shelves overflowing with books arranged both horizontally and vertically for optimal use of space. The resulting abundance gives books a similar appearance to many other items on sale in open-air markets. Looking for a specific book on Abderrahmane's crammed bookshelves, I was unable to discern his system of organization, but when I asked for help, he immediately pointed to a specific area and declared, "Pocket books are over there!" Abderrahmane organizes his books by series by according to formats and colors. "Here are the Pocket editions, there are the red J'ai Lu, and here are the 'great novels,'" Abderrahmane pointed out, referring to their size. He added, "Harlequins cost 10 MAD, great novels, 25 MAD, Livres de poche [small-format trade paperbacks], 20 MAD, and Folios, 25 or 30 MAD." Despite the impression of disorder, his books are arranged pragmatically following strict categories that facilitate daily work.

Observing Abderrahmane's interactions with customers confirmed his deep familiarity with his inventory. When I asked him why some books are more expensive than others, he replied, "because they're new!" i.e., "in good condition." Displayed on the most accessible table in his shop, I found books by well-known authors who were fluently cited by Abderrahmane, including Barbara Cartland, Agatha Christie, Driss Chraïbi, Tahar Ben Jelloun, and Naguib Mahfouz (in French). In fact, it became clear that although he is not literate in French, he organizes his boutique and prices his books according to three criteria: Author celebrity, physical appearance and characteristics, and condition. Although he lacks specific knowledge about the contents of his inventory, he perfectly masters books as physical objects, and this knowledge and expertise enables him to identify and categorize every item, including the fact that some authors have published several books within a given series.

Like Mohamed the kiosquier, Abderrahmane is far more familiar with books' exterior than with what lies inside them. Color and format are used to distinguish books from each other, classify them, and organize them, as well as to assign prices, all of which derive from professional expertise. 10 Passers-by frequently exchange articles with each other and hold conversations in front of the magazine and book displays along the sidewalks. The public presence of so much printed matter encourages discussions about current events that range from political to moral to religious and are sometimes led by the vendors. This role is one illustration of the status of kiosquiers, terrassiers and bouquinistes as "public figures," to use Mitchell Duneier's term for street book and magazine vendors in a New York neighborhood in the late 1990s. Such figures are active participants in urban intellectual life and help maintain the social order [2000]. As central figures in the urban distribution of printed matter, street vendors in Casablanca and Rabat provide readers who are not always highly literate access to literacy artifacts and processes that encompass censored authors and minority languages. My explorations of kiosquiers', terrassiers', and bouquinistes' daily work confirms that books remain important features of the lives of the large number of non-literate and semi-literate vendors who are responsible for the circulation of print-and ideas-in these two Moroccan cities. Publishers have become highly conscious of the singular methods used by terrassiers, kiosquiers, and bouquinistes to organize books according to physical characteristics, and their work habits and practices shape and are shaped by publishers' cover layout and marketing decisions. Because the material presence of books plays such an important role in the distribution of print, publishers, kiosquiers, terrassiers, and bouquinistes are ultimately partners in creating and promoting the popular esthetics of the book.

Presiding over their printed wares on urban sidewalks and using every available means to organize and sell them, these vendors maintain also close connections to more formal sales channels and exert a significant influence over the cultural lives of Rabat and Casablanca. Far from being in a submissive position with respect to intellectual and institutional authorities, they are what de Certeau labeled "poachers" [START_REF] Michel De | L'Invention du quotidien[END_REF] who appropriate knowledge objects and make them available in original ways, including diversion and subterfuge, because "knowledge does not exist without the actors who practice them, and beyond their immediate finality, such practices reflect the subtle distribution of roles, skills, and authority in a given community" [Jacob, 2011: 20]. This distribution of roles and expertise in the circulation of knowledge in Rabat and Casablanca is the domain over which the terrassiers, kiosquiers, and bouquinistes preside amid the teeming markets, streets, and sidewalks of two Moroccan cities. ■ Notes 1. The same word is used for the point of sale and the vendor.

2. This approach is the subject of my 2016 book. Anouk Cohen, Fabriquer le livre au Maroc, Paris: Karthala, "Terres et gens d'islam." 3. It was estimated in 1998 that there was one French reader for every three Arabiclanguage readers in Rabat and Casablanca [START_REF] Yazami | Enquête sur la lecture au Maroc[END_REF]]. This ratio favors Arabic due to Arabization policies.

4. For a detailed study of the world of Moroccan books-in the sense in which Howard [START_REF] Becker | Les Mondes de l'art[END_REF] uses the notion of "Art Worlds," as networks of actors who cooperate in the existence of a work of art, see Cohen (2016). The Moroccan book business has four principal characteristics: It is young and changing, and it is urban and divided into two distinct linguistic domains. The current development of a new publishing market is linked to the recent growth in literacy rates and school attendance in the country. Averages mask vast differences between cities and rural areas and between capitals, which are highly literate, and the rest of the country. The Moroccan book market is developing within a specific urban framework, essentially the axis between Rabat and Casablanca. These two northern cities contain 90% of the publishers and the most highly developed network of bookstores. I chose them as sites for my ethnographic analysis for these reasons. It is also along this axis that the largest literate segments of the populations, who read and write principally in two languages-Arabic and French. In addition to being young and urban and in a period of great change, local publishing is divided between Arabic-speaking and francophone sectors, a division that permeates the entire distribution chain, from fabrication of distribution and reception. A very small minority of publishers and wholesale or retail distributors, as well as authors and readers, work and read in both languages.

5. The name used to refer to Muslims who have made the pilgrimage to Mecca.

6. Although Morocco's first language was Amazigh, it had no well-defined status until recently beyond functioning as a daily common language for rural vernacular Amazighophone communities living amid urban communities. Since the royal speech in 2001 and the establishment of the Royal Institute of Amizagh Culture in 2008, Amizagh has been formally recognized. As noted earlier, following popular uprisings, Mohammed VI designated Amizagh as the second official language of Morocco on June 17, 2011.

7. The Western Sahara is an area in Northwestern Africa that shares a border with Morocco to the north, with Algeria to the northeast, Mauritania to the south, and with the Atlantic Ocean to the west. A non-autonomous territory according to the United Nations, this former Spanish colony does not have definitive legal status more than thirty years after the Spanish departed in 1976. It is claimed by both Moroccan and by the Sahrawi Democratic Arabic Republic (SDAR), which was founded by the Polisario Front in 1976. The Polisario Front was militarily, financially, and diplomatically supported by Algeria, with the goal of total independence for Western Sahara. Since the 1991 cease-fire, Morocco controls and administers approximately 80% of the territory and, behind a long security zone, the Polisario Front currently controls the remaining 20%.

The gap between what should be kept

secret and what should be revealed has become imperceptible. From one day to the next, the authorities' attitude vacillates between indulgence and rigidity amid overall arbitrariness. According to a journalist who resides in Casablanca: "With Hassan II, the red lines that you could not cross were clear. Since the beginning of Mohammed VI's reign, things are vague. We know that they exist but we do not know where they are. We only understand retrospectively, once we've gone past them." For more information, see Cohen [2011]. 9. According to the official report 50 ans de développement humain au Maroc (2006) [Fifty Years of Human Development in Morocco], nearly 43% of the population over 10 years old is illiterate. This statistic masks greater disparities, however, between cities (29% of the total population) and rural areas, which represent 61%. Furthermore, the illiteracy rate is declining among young people, particularly between 10 to 15 years of age-the rate was 36% in 1994 and 13% in 2007. See 50 ans de développement humain au Maroc (2006), for complete data. 10. See Cohen (2016) for more information about the relationship between oral and written language in urban Moroccan settings.

RÉSUMÉ

Terrassiers, kiosquiers et bouquinistes à Rabat et à Casablanca. Circulation du savoir et matérialité du livre À Rabat et à Casablanca, capitales administratives et économiques du Maroc, une grande partie de la production éditoriale, des journaux et des magazines est écoulée directement dans la rue, sur les trottoirs et dans les kiosques. Le nombre élevé de kiosquiers, terrassiers et bouquinistes (suivant la terminologie employée localement) indique que leurs commerces ne constituent pas un mode de diffusion marginal contrairement à ce que leur aspect précaire pourrait laisser croire. Le but de cet article est de mieux cerner le rôle crucial que ces marchands de rue, souvent analphabètes ou illettrés, jouent dans la circulation de l'écrit dans ces villes marocaines.

Mots-clefs : Marchands de livres. Circulation du savoir. Matérialité. Analphabétisme. Maroc.

ZUSAMMENFASSUNG

Zeitschriften-und Buchhändler in Rabat und Casablanca. Wissensvermittlung und die Materialität von Büchern

In Rabat und Casablanca, jeweils Verwaltungs-und Wirtschaftshauptstadt Marokkos, wird ein großer Anteil der schriftlichen Produktion, Zeitungen und Zeitschriften direkt auf der Straße, auf Bürgersteigen und in Kiosken verkauft. Der hohe Anteil von Zeitschriften-und Buchhändlern auf der Straße zeigt auf, dass ihr Handel keine marginalisierte Verkaufsform ist, auch wenn die prekäre Lage dies vermuten ließe. Ziel dieses Artikels ist es, die zentrale Rolle dieser Straßenhändler, die häufig keine Schulbildung haben oder Analphabeten sind, für die Verbreitung von Schriften in den marokkanischen Städten aufzuzeigen.

Stichwörter: Buchhändler. Wissensvermittlung. Materialität. Analphabetismus. Marokko.

RESUMEN

Libreros de terrazas, de kioscos y libreros de viejo en Rabat y Casablanca. Circulación del saber y materialidad del libro En Rabat y Casablanca, capitales administrativas y económicas de Marruecos, gran parte de la producción editorial, periódicos y revistas se despacha directamente en la calle, en las aceras y los kioscos. El número importante de libreros de terrazas, de kioscos y libreros de viejo (según la terminología empleada localmente) indica que sus negocios no constituyen un modo de difusión marginado, al contrario de lo que sugiere su aspecto precario. El objetivo de este artículo es definir mejor el papel crucial que estos vendedores de calle, muchas veces analfabetos o iletrados, cumplen en la circulación del escrito en estas ciudades marroquíes.

Palabras-clave : Vendedores de libros. Circulación del saber. Materialidad. Analfabetismo. Marruecos.

  Photo 3 -Mohamed, kiosquier on the Avenue Mohammed V in Casablanca(author photo, March 15, 2007).

Photo 4

 4 Photo 4 Example of book covers "Passage of miracles"Ruelles Midaq

  Sahara as part of Morocco. And then some books about religion. Now, things are freer but you aren't going to find any copies of Salman Rushdie's Satanic Verses or pornography in Morocco! Absolutely none! But now I know what to import and I know what's banned. It's self-censorship.

Document downloaded from www.cairn-int.info -INIST-CNRS --193.54.110.56 -20/11/2019 12h14. © P.U.F.

Photo 1 -Terrassier on the Avenue Hassan II in Rabat (author photo, October 5, 2015).Document downloaded from www.cairn-int.info -INIST-CNRS --193.54.110.56 -20/11/2019 12h14. © P.U.F.