Stephan N Steinmann

Carine Michel
email: carine.michel@ens-lyon.fr

Viewpoint: How to gain atomistic insights on reactions at the water/solid interface?

Keywords: Solvation, solid/water interface, catalysis

Reactions at the water/solid interface are central to the development of sustainable processes, from biomass upgrading to photo-and electrocatalysis. To gain atomistic insight in these reactions, modelling approaches have been constantly improved over the past decade. Polarisable continuum models have considerably improved the description of charge separation and enabled a proper inclusion of the surface polarisation in electrochemistry and photocatalysis. Micro-solvation has been used to probe the impact of H-bonding at the water/catalyst interface, a key ingredient to explain observed solvent effects in liquid heterogeneous catalysis. Last, considerable efforts have been dedicated to reach a full atomistic description of the water/liquid interface, allowing the evaluation of activation energies of catalytic reactions and catalyst decomposition. In this Viewpoint, we illustrate advantages and limitations of current methods and provide perspectives.

View Point

Aqueous interfaces are ubiquitous and central to a wide range of important and challenging processes: rock weathering in geochemistry, bio-compatibility of materials, and in aqueous phase heterogeneous catalysis including biomass upgrading, electro-and photocatalysis. [START_REF] Björneholm | Water at Interfaces[END_REF][START_REF] Calvin | Review of surface water interactions with metal oxide nanoparticles[END_REF][START_REF] Gonella | Water at charged interfaces[END_REF] The fundamental knowledge of these interfaces is surprisingly limited compared to solid/gas interfaces and bulk water. For example, open questions remain regarding the water structuring, the possible water dissociation at the interface, the impact of an applied electrochemical potential on this interfacial structure and the consequences of interfacial solvation effects on catalytic reactions. [START_REF] Gonella | Water at charged interfaces[END_REF] Standard surface sciences techniques (STM, vibrational and X-Ray spectroscopy, etc.) cannot be easily applied to the solidliquid interface. [START_REF] Björneholm | Water at Interfaces[END_REF] Nevertheless, they can provide valuable information about the interaction of water with surfaces under surface-science conditions (low pressure). [START_REF] Maier | How Does Water Wet a Surface?[END_REF] For instance, in conjunction with DFT calculations, [START_REF] Feibelman | Partial dissociation of water on Ru[END_REF][START_REF] Michaelides | Different surface chemistries of water on Ru[0001]: from monomer adsorption to partially dissociated bilayers[END_REF] several groups have found that water dissociates above 150 K and forms a mixed (OH/H/H 2 O) overlayer on Ru(0001). [START_REF] Maier | How Does Water Wet a Surface?[END_REF] Still, surface sciences techniques are limited to one or few layers of water at low temperature, which is a questionable approximation for liquid water at room temperature or typical reaction conditions for biomass transformations, which can reach ∼ 200 • C in an autoclave. [START_REF] Thapa | C6 Diacids from homocitric acid lactone using relay heterogeneous catalysis in water[END_REF] Other methods can be used (e.g. calorimetry and inelastic neutron scattering [START_REF] Calvin | Review of surface water interactions with metal oxide nanoparticles[END_REF] ) and some are even specifically designed to be sensitive to the interfacial signal, such as non-linear optical spectroscopies [START_REF] Shen | Sum-Frequency Vibrational Spectroscopy on Water Interfaces: Polar Orientation of Water Molecules at Interfaces[END_REF][START_REF] Zaera | Probing Liquid/Solid Interfaces at the Molecular Level[END_REF] and surface sensitive X-Ray diffraction methods. [START_REF] Zaera | Probing Liquid/Solid Interfaces at the Molecular Level[END_REF][START_REF] Pham | Integrating Ab Initio Simulations and X-ray Photoelectron Spectroscopy: Toward A Realistic Description of Oxidized Solid/Liquid Interfaces[END_REF] In all these studies, modelling appears as a corner-stone to convert the experimentally measured signals into an atomistic understanding of aqueous interfaces involved in catalysis. Several modelling approaches have been developed and used in the past decade. We here discuss how to choose the best method depending on the expected role of water on the reaction investigated at the catalyst/water interface, building on the experience we accumulated during the past years on a wide range of systems.

To model reactions at the catalyst/water interface, implicit solvent models, also known as polarisable continuum models (PCM), have been used increasingly since it was first implemented in a major periodic DFT software in 2014, [START_REF] Mathew | Implicit solvation model for density-functional study of nanocrystal surfaces and reaction pathways[END_REF] and is now available in various flavors in a wide variety of codes. [START_REF]ENVIRON -Home[END_REF][13][14][START_REF] Gpaw | DFT and beyond within the projector-augmented wave method[END_REF] Implicit solvation models are very convenient and valuable when the main effect of the solvent is expected to be the stabilization of (partially) charged species such as in electrocatalysis as reviewed by Ringe et al., [START_REF] Ringe | Implicit Solvation Methods for Catalysis at Electrified Interfaces[END_REF] including when modelling transition states. [START_REF] Abidi | How are Transition States Modelled in Heterogeneous Electrocatalysis?[END_REF] In the PCM, the average interaction between a solute and the solvent is modelled by two terms: an average electrostatic interaction that leads to a stabilization of the solute, supplemented by the so-called cavitation energy, which accounts for all the energy penalty terms (repulsion, creation of a cavity in the solvent etc.) While the electrostatic interaction can be computed by the Poisson-Boltzmann equation, the cavitation energy generally relies on semi-empirical parameters, fitted to molecular benchmark data. [START_REF] Ringe | Implicit Solvation Methods for Catalysis at Electrified Interfaces[END_REF] In practice it turns out that the cavitation energy is generally negligible compared with the electrostatic interaction. [START_REF] Steinmann | Solvation free energies for periodic surfaces: comparison of implicit and explicit solvation models[END_REF][START_REF] Gu | Group Additivity for Aqueous Phase Thermochemical Properties of Alcohols on Pt(111)[END_REF] However, the definition of the solute cavity, and thus the transition of the dielectric constant from its vacuum value (in the solute) to the bulk solvent value, directly impacts the quality of the implicit solvent model, [START_REF] Andreussi | Revised self-consistent continuum solvation in electronic-structure calculations[END_REF][START_REF] Vassetti | Assessing the performances of different continuum solvation models for the calculation of hydration energies of molecules, polymers and surfaces: a comparison between the SMD, VASPsol and FDPB models[END_REF] including work functions [START_REF] Bramley | Reconciling Work Functions and Adsorption Enthalpies for Implicit Solvent Models: A Pt (111)/Water Interface Case Study[END_REF] and adsorption energies. [START_REF] Bramley | Understanding Adsorption of Organics on Pt(111) in the Aqueous Phase: Insights from DFT Based Implicit Solvent and Statistical Thermodynamics Models[END_REF] While machine-learning seems to be able to replace implicit solvents for neutral molecules, [START_REF] Chen | Machine learning implicit solvation for molecular dynamics[END_REF] the lack of a physical description of electrostatics seems difficult to reconcile with electrified interfaces. The later are, however, a stronghold of implicit solvents as recently reviewed in detail. [START_REF] Schwarz | The electrochemical interface in first-principles calculations[END_REF] Indeed, the implicit solvent ensures a reasonable capacitance (relation between applied potential and surface charge) [START_REF] Lespes | Using Implicit Solvent in Ab Initio Electrochemical Modeling: Investigating Li+/Li Electrochemistry at a Li/Solvent Interface[END_REF] and allows a consistent, black-box, treatment of the solvent for all reactants and intermediates, [START_REF] Jinnouchi | Electronic structure calculations of liquid-solid interfaces: Combination of density functional theory and modified Poisson-Boltzmann theory[END_REF][START_REF] Wang | Formic Acid Oxidation at Pt/H2O Interface from Periodic DFT Calculations Integrated with a Continuum Solvation Model[END_REF] equally applicable to water [START_REF] Steinmann | Modeling the HCOOH/CO 2 Electrocatalytic Reaction: When Details Are Key[END_REF] and organic solvents. [START_REF] Steinmann | Impacts of electrode potentials and solvents on the electroreduction of CO 2 : a comparison of theoretical approaches[END_REF] As an example, we have exploited the implicit solvent model to investigate the electro-chemical potential dependence of the electro-oxidation of formic acid, typical for direct formic acid fuel cells. [START_REF] Steinmann | Modeling the HCOOH/CO 2 Electrocatalytic Reaction: When Details Are Key[END_REF] In this study we could demonstrate that the reaction mechanism on Ni(111) crucially depends on the reorientation of the formate intermediate, a formally "chemical" reaction step, which nevertheless shows a non-negligible potential dependence. This importance of the electrochemical potential on formally chemical steps has also been observed for the reductive coupling of CO 2 on copper, [START_REF] Goodpaster | Identification of Possible Pathways for C-C Bond Formation during Electrochemical Reduction of CO 2 : New Theoretical Insights from an Improved Electrochemical Model[END_REF] suggesting the general importance of accounting for the electrode polarisation. We have also relied on an implicit solvent description to elucidate why increasing the pH increases thermal formic acid decomposition into CO 2 and H 2 on Pd(111). [START_REF] Wang | Key role of anionic doping for H 2 production from formic acid on Pd (111)[END_REF] At a pH above the pKa of formic acid, anionic formate can be chemisorbed at the Pd/water interface. Detailed analysis has revealed that the interaction between the surface dipole moment of the adsorbate with the electric field generated by the adsorption of anionic species results in a lowering of the limiting transition states. This study relied on the capability of rigorously computing the energy of a charged periodic surface through the inclusion of an effective neutralizing counter-charge, obtained by the solution of the linearized Poisson-Boltzmann equation. [START_REF] Mathew | Implicit selfconsistent electrolyte model in plane-wave density-functional theory[END_REF] Furthermore, we have demonstrated for two potential-dependent overlayers on Au(111) immersed in an aqueous electrolyte, that this approach yields semi-quantitative agreement with experiments, [START_REF] Steinmann | Assessing a First-Principles Model of an Electrochemical Interface by Comparison with Experiment[END_REF][START_REF] Fang | Revisiting the atomistic structures at the interface of Au(111) electrode-sulfuric acid solution[END_REF] a conclusion that has also been reached for CO 2 reduction intermediates over copper. [START_REF] Baricuatro | Operando Electrochemical Spectroscopy for CO on Cu(100) at pH 1 to 13: Validation of Grand Canonical Potential Predictions[END_REF] Therefore, we advocate the use of implicit solvents for investigating the potential dependence of electrocatalytic reactions, [START_REF] Abidi | Atomistic modeling of electrocatalysis: Are we there yet?[END_REF] including the reactivity on semi-conductors under photo-electrocatalytic conditions, such as oxygen evolution reaction (OER) over the CoOOH co-catalyst. [START_REF] Curutchet | Two-Sites Are Better Than One: Revisiting the OER Mechanism on CoOOH by DFT with Electrode Polarization[END_REF] For this catalytic system we have demonstrated the importance of considering chemical steps, in particular the formation of the O-O bond and the desorption of O 2 and revealed the involvement of two, rather than only one, Co site for the most probable reaction pathway.

Water can also play a major role as a competitive adsorbate. To gain a thorough understanding of this effect, we need to explicitly describe water molecules. Moving to classical molecular mechanics (MM) is then a natural choice to avoid the large computational burden associated with ab initio molecular dynamics. However, pair-wise force fields fail to properly describe chemisorption of intermediates relevant to Catalysis. Therefore, we have proposed a QM/MM approach (MMSolv) to keep a high-level (DFT) description of the surface/adsorbate interaction in combination with solvation effects at the MM level, similar in spirit to the work of the Heyden [START_REF] Saleheen | Liquid-Phase Modeling in Heterogeneous Catalysis[END_REF] and Getman 40 groups. In practice, MM-Solv combines ab initio adsorption energies with solvation energies computed at the MM level using an alchemical transformation (see Fig. 1). [START_REF] Steinmann | Solvation free energies for periodic surfaces: comparison of implicit and explicit solvation models[END_REF] Of course, the reliability of the obtained results strongly depends on the quality of the force field. Most of the water/metal force fields do not reproduce the near chemisorption of the water/metal interaction observed with DFT. [START_REF] Steinmann | Force Field for Water over Pt(111): Development, Assessment, and Comparison[END_REF] Our GAL17 force field has been specifically designed to retrieve the strength and angular dependence of this interaction. [START_REF] Steinmann | Force Field for Water over Pt(111): Development, Assessment, and Comparison[END_REF][START_REF] Clabaut | Ten Facets, One Force Field: The GAL19 Force Field for Water-Noble Metal Interfaces[END_REF] The water/metal interaction is strong enough to challenge the standard alchemical transformation, so that we had to pass through a well-behaved physisorption potential for Pt/water in order to achieve converged, reproducible results. [START_REF] Clabaut | Solvation Free Energies and Adsorption Energies at the Metal/Water Interface from Hybrid Quantum-Mechanical/Molecular Mechanics Simulations[END_REF] This MMSolv strategy has been validated against experimental data on the adsorption of aromatics at the Pt/water interface. [START_REF] Clabaut | Solvation Free Energies and Adsorption Energies at the Metal/Water Interface from Hybrid Quantum-Mechanical/Molecular Mechanics Simulations[END_REF][START_REF] Singh | A Simple Bond-Additivity Model Explains Large Decreases in Heats of Adsorption in Solvents Versus Gas Phase: A Case Study with Phenol on Pt(111) in Water[END_REF][START_REF] Singh | Quantifying Adsorption of Organic Molecules on Platinum in Aqueous Phase by Hydrogen Site Blocking and in Situ X-ray Absorption Spectroscopy[END_REF] MMSolv performs noticeably better than PCM thanks to a proper inclusion of the surface solvation. It can be easily used with oxides surfaces, given that the chemisorption of water is well described. [START_REF] Rey | Transferable Gaussian Attractive Potentials for Organic/Oxide Interfaces[END_REF] When considering the adsorption of flexible molecules (e.g. polyols), MMsolv can easily be combined with our package DockOnSurf [START_REF] Marti | A Python code for the High-Throughput Screening of Flexible Molecules Adsorbed on Surfaces[END_REF] to automate the sampling of conformers. Currently, MMsolv is, however, not directly applicable to the adsorption of ions, since an electrostatic embedding is missing. [START_REF] Galvan | A program for the calculation of solvent effects combining QM/MM methods and the mean field approximation[END_REF][START_REF] Gim | Multiscale Simulation Method for Quantitative Prediction of Surface Wettability at the Atomistic Level[END_REF] Another limitation remains the quality of the classical force field. Our GAL force field [START_REF] Steinmann | Force Field for Water over Pt(111): Development, Assessment, and Comparison[END_REF] was a clear improvement compared to existing Pt/water force fields. Nevertheless, we have shown recently that many-body interactions (polarisability and the charge transfer) contribute up to about 50 % to the adsorption energy of water layers on Pt(111), [START_REF] Clabaut | Water adlayers on noble metal surfaces: Insights from energy decomposition analysis[END_REF] an effect that is beyond the capabilities of pair-wise additive GAL force fields. Importantly, the charge transfer scales with the polarisability. Hence, developing polarisable force fields (e.g., in the spirit of AMOEBA [START_REF] Liu | Implementation of Geometry-Dependent Charge Flux into the Polarizable AMOEBA+ Potential[END_REF] ) could be a valuable approach to improve the description of metal/water interfaces.

Impact of the Solvation on Adsorption Energies

Our target in this work is to assess the impact of the water solvent on the adsorption reaction of a given substrate (here levulinic acid, named LA in the following) on a surface (here Ru(0001)). This process can be described by the following reaction:

LA solv + Ru(0001) solv ! LA@Ru(0001) solv
Since the free energy of adsorption in vacuum is much more accessible than the one in solvent, it is customary to write the Gibbs free energy of adsorption in solution DG solv ⇤ ads as the following sum

DG solv ⇤ ads = DG vac ⇤ ads + DDG ads ⇤ solv ( 8
)
where DG vac ⇤ ads is the Gibbs free energy of adsorption in vacuum and DDG ads ⇤ solv corresponds to the variation of the solvation Gibbs free energy DG ⇤ solv along the adsorption process. Since we have no data for a comparison with experiment for adsorption energies, we do not include any terms that affect all the schemes to the same extent. This implies that thermal effects (e.g., entropy of adsorption) are neglected in the present approach, but could be included at least An alternative to improve the description of the direct interactions between chemisorbed species and water is to add a few water molecules to be described at the ab initio level.

9 Ab initio MMSolv MM H 2 O H 2 O H 2 O H 2 O H 2 O H 2 O

Pt

This approach, often coined micro-solvation, has been originally used to describe solvation effects in homogeneous aqueous phase. For instance, micro-solvation was successfully used in combination with a PCM to compute the aqueous acid dissociation constants. [START_REF] Kelly | Adding explicit solvent molecules to continuum solvent calculations for the calculation of aqueous acid dissociation constants[END_REF] This is how we have investigated the impact of water on the transformation of oxygenated compounds catalysed by metals for the past 10 years. [START_REF] Michel | H versus O-H Bond Dissociation for Alcohols on a Rh(111) Surface: A Strong Assistance from Hydrogen Bonded Neighbors[END_REF][START_REF] Zaffran | Linear Energy Relations As Predictive Tools for Polyalcohol Catalytic Reactivity[END_REF][START_REF] Loffreda | Tuning catalytic reactivity on metal surfaces: Insights from DFT[END_REF][START_REF] Michel | Role of water on metal catalyst performance for ketone hydrogenation. A join experimental and theoretical study on levulinic acid conversion into gamma-valerolactone[END_REF][START_REF] Gu | Unraveling the Role of Base and Catalyst Polarization in Alcohol Oxidation on Au and Pt in Water[END_REF][START_REF] Schweitzer | Can microsolvation effects be estimated from vacuum computations? A case-study of alcohol decomposition at the H 2 O/Pt(111) interface[END_REF] Importantly, adding explicitly one water molecule has allowed us to rationalize solvent effects in ketone hydrogenation. [START_REF] Michel | Role of water on metal catalyst performance for ketone hydrogenation. A join experimental and theoretical study on levulinic acid conversion into gamma-valerolactone[END_REF] Figure 2 was not found to significantly impact on the activation and reaction energies compared with vacuum. [START_REF] Gu | Group Additivity for Aqueous Phase Thermochemical Properties of Alcohols on Pt(111)[END_REF] The largest modification is found for a C-C bond splitting (CH 3 -COH),

with a decrease of 0.22 eV of the reaction energy. This can be related to a change in the orientation of the hydroxyl group that reduces its stabilizing interactions with PCM. To improve the description of H-bonding between the water solvent and the solute, we have systematically added one water molecule, preferentially chemisorbed on a neighbouring top site. In the presence of micro-solvation, the impact of water was considerably stronger than when using only PCM. [START_REF] Schweitzer | Can microsolvation effects be estimated from vacuum computations? A case-study of alcohol decomposition at the H 2 O/Pt(111) interface[END_REF] The largest effect we identified is an increase of 0.53 eV of the activation barrier of a C-O bond dissociation (CH 3 CH 2 -O). This can be related to a stabilization of the initial state that is greater than the stabilization of the transition state.

This example is representative of the dissociation of C-O bonds, but not of C-OH bonds.

In this later case, the resulting OH fragment is stabilized through a very strong H-bond, which facilitates the C-OH bond cleavage. This micro-solvation approach can be used in a wide range of context to include the direct interactions between chemisorbed species and water, as for instance to address the competition between decarboxylation and decarbonylation in acetic acid over Pd(111), [START_REF] Chukwu | Effects of Co-adsorbed Water on Different Bond Cleavages of Oxygenates on Pd (111)[END_REF] to predict onset potentials in electrocatalysis, [START_REF] Rendón-Calle | Substantial improvement of electrocatalytic predictions by systematic assessment of solvent effects on adsorption energies[END_REF] or to study the adsorption of a corrosion inhibitor. For many reactions, water is a non-innocent solvent. In other words, its impact goes beyond the stabilization of surface species through electrostatic effects and H-bonding:

water and other protic solvents can also react, act as a co-catalyst and modify the reaction mechanism. [START_REF] Xie | Discovery of a New Solvent Co-Catalyzed Mechanism in Heterogeneous Catalysis: A First-Principles Study with Molecular Dynamics on Acetaldehyde Hydrogenation on Birnessite[END_REF] This is well known in the catalytic oxidation of alcohols in water when using O 2 as a oxidant. Isotopic labelling experiments have demonstrated that the oxygen atom that is incorporated in the carboxylic acid product is mainly coming from water and not from O 2 . [START_REF] Zope | Reactivity of the Gold/Water Interface During Selective Oxidation Catalysis[END_REF] The presence of water facilitates the O --O splitting not only thanks to a stabilizing H-bond network but also through a proton transfer. On Au(111), we have shown that a first proton is transferred from H 2 O to O 2 yielding OH and HOO. Then, the O-O bond cleavage in OOH is facilitated by a concomitant proton transfer from a second water molecule, generating in total 4 OH. These chemisorbed OH are the oxidizing species at the Au/water interface. [START_REF] Gu | Unraveling the Role of Base and Catalyst Polarization in Alcohol Oxidation on Au and Pt in Water[END_REF] The presence of water facilitates the O 2 activation on Au(111) since the overall barrier to generate the four OH is 0.86 eV while the O 2 splitting into two chemisorbed O was found above 1 eV by Zope et al. [START_REF] Zope | Reactivity of the Gold/Water Interface During Selective Oxidation Catalysis[END_REF] This barrier is even lower in presence of a base (0.74 eV), when the adsorption of a hydroxide anion polarises the Au/water interface. [START_REF] Gu | Unraveling the Role of Base and Catalyst Polarization in Alcohol Oxidation on Au and Pt in Water[END_REF] Modeling the aqueous environment using micro-solvation has well-known limitations: the number and position of the water molecules has to be chosen, making its usage clumsy and the results can depend on these somewhat arbitrary choices in an unpredictable manner, in particular when proton-transfers are involved. Even combined with PCM, micro-solvation cannot properly describe solvation shells with changing size, the surface solvation or long-range proton transfers in water (Grotthus mechanism).

Thus, moving to a full ab initio description of the liquid water is appealing, since in this case each water molecule could react. In principle, ab initio molecular dynamics (AIMD) addresses all the limitations we listed so far. However, the main bottleneck of AIMD is to reach a representative phase-space sampling, which requires sufficiently long MDs. Recently, the usefulness of AIMD for heterogeneous catalysis at the water/solid interface has significantly increased thanks to enhanced-sampling methods and efficient compu-tational resources and softwares. For instance, AIMD can be enhanced using thermodynamics integration or umbrella sampling, which require a good pre-knowledge of the reaction coordinate. [START_REF] Xie | Discovery of a New Solvent Co-Catalyzed Mechanism in Heterogeneous Catalysis: A First-Principles Study with Molecular Dynamics on Acetaldehyde Hydrogenation on Birnessite[END_REF] in aqueous phase relative to the gas phase. In this study, a full slab of liquid water (80 water molecules) is added on top the Au 11 /TiO 2 system, and the O-O distance is a natural choice for the reaction coordinate. However, thermodynamic integration is limited to a single reaction step, [START_REF] Sprik | Free energy from constrained molecular dynamics[END_REF] and the reaction coordinate needs to be straightforward. For instance, in the O 2 dissociation case, the H transfer is only observed if it happens in the reachable timeframe (< 20 picoseconds). We recently faced this issue when attempting to describe the desorption of ethanol from the alumina/water interface to the bulk water. [START_REF] Rey | Mechanistic investigation and free energies of the reactive adsorption of ethanol at the alumina/water interface[END_REF] It turned out to be a challenging process for thermodynamic integration because of the very slow dynamics of interfacial water molecules. [START_REF] Réocreux | Structuration and Dynamics of Interfacial Liquid Water at Hydrated γ-Alumina Determined by ab Initio Molecular Simulations: Implications for Nanoparticle Stability[END_REF] We employed the altitude as the natural reaction coordinate. The gas-phase adsorption mode and site was taken as a starting configuration for a slow-growth AIMD. Still, the replacement of chemisorbed ethanol by chemisorbed water (or dissociated water) requires a strong reorganisation of the solvation shell that cannot be reached in the accessible time frame, yielding to a spurious barrier. A first solution is to trigger this reorganisation "by hand", making the assumption that water diffusion at the interface is much faster than the desorption. However, the water diffusion is considerably slowed down at the interface compared to the bulk solution, [START_REF] Réocreux | Structuration and Dynamics of Interfacial Liquid Water at Hydrated γ-Alumina Determined by ab Initio Molecular Simulations: Implications for Nanoparticle Stability[END_REF] so that the validity of this hypothesis is uncertain. An alternative is to move to metadynamics, [START_REF] Bussi | Using metadynamics to explore complex free-energy landscapes[END_REF] where additional reaction coordinates can be included to bias (and thus accelerate the sampling off) changes in solvation. [START_REF] Rey | Mechanistic investigation and free energies of the reactive adsorption of ethanol at the alumina/water interface[END_REF] Last, water can even modify the catalyst surface. For instance, combining explicit water molecules and an implicit solvent model, we have provided evidence that sulfur atoms on edges of MoS 2 will be gradually replaced by hydroxyl groups under hydrogen evolution reaction conditions. [START_REF] Abidi | Revisiting the active sites at the MoS 2 /H 2 O interface via grand-canonical DFT: The role of water dissociation[END_REF][START_REF] Abidi | How Stable Are 2H-MoS 2 Edges under Hydrogen Evolution Reaction Conditions?[END_REF] Complementing the micro-solvation with a continuum model has been mandatory in this case to properly describe the polarisation of the electrified interface. This combination of micro-sovlation and PCM is a valuable tool to investigate the stability of active sites in aqueous solution but it cannot easily determine the corresponding activation energies and thus might miss kinetic bottlenecks. Furthermore, how a robust combination of implicit and explicit solvation can be achieved at electrified interfaces remains a subject of active research, [START_REF] Gauthier | Challenges in Modeling Electrochemical Reaction Energetics with Polarizable Continuum Models[END_REF] last but not least because the implicit solvent should not penetrate between the explict solvent molecules. [START_REF] Andreussi | Solvent-Aware Interfaces in Continuum Solvation[END_REF] Accelerating the phase-space exploration along several variables, ab initio metadynamics enables modelling of such multi-step complex reactions at the catalyst/water interface as demonstrated on the first steps of γ-Al 2 O 3 hydrolysis. [START_REF] Réocreux | Reactivity of shape-controlled crystals and metadynamics simulations locate the weak spots of alumina in water[END_REF] The γ-Al 2 O 3 (110) surface exposes two tetrahedral aluminum atoms (Al α and Al β ) in contact with water. [START_REF] Wischert | γ-Alumina: The Essential and Unexpected Role of Water for the Structure, Stability, and Reactivity of Defect Sites[END_REF] During hydrolysis, the coordination number (CN) of these aluminum atoms with water should increase, while the CN with the oxygen of alumina should decrease. Using these two variables, we explored the reactivity of the two tetrahedral aluminum atoms and identified the most sensitive Al atom on the (110) surface (named Al β in Figure 3). The two-dimensional free energy surface landscapes are shown in Figure 3. While only one free energy well is obtained when biasing the CNs of Al α , several wells are obtained when biasing the CNs of Al β , demonstrating that Al β is the weak-spot for γ-Al 2 O 3 decomposition via hydration.

The corresponding free energy surface provides the mechanism (addition/elimination sequence) and the barriers (∼80 kJ•mol -1 , see Figure 3d).

Ab initio metadynamics appears as the method of choice when water is involved as a reactant. Still, it is challenging to set up since the description of the reactions relies on only few variables to describe complex multi-step mechanisms. For cases where water is not reacting, we have recently developed MMSolv, a hybrid scheme that combines ab for liquid water at room temperature, but is computationally much cheaper and gives easily access to the solvation energies of arbitrary adsorbates. MMSolv relies on MM and alchemical transformation to compute the solvation term. So far, it implements a basic mechanical embedding but it could be upgraded to an electrostatic embedding, in particular to be used for electrified interfaces and the adsorption of ions. A more serious drawback is that the reliability of the results strongly depends on the quality of the force field. Therefore, more accurate force fields are clearly needed. Regarding water/metal force fields, a first step is to move to polarizable force fields. This was recently proposed by Goddard and co-workers in the context of electrocatalysis. [START_REF] Naserifar | Artificial Intelligence and QM/MM with a Polarizable Reactive Force Field for Next-Generation Electrocatalysts[END_REF] Another possibility is to move to machine learning potentials [START_REF] Unke | Machine Learning Force Fields[END_REF] as proposed by Behler and co-workers to describe the Cu/water interface, [START_REF] Natarajan | Neural network molecular dynamics simulations of solid-liquid interfaces: water at low-index copper surfaces[END_REF] a strategy that has lead to valuable insight into the hydrogen coupling at the platinum/water interface. [START_REF] Rice | Hydrogen Coupling on Platinum Using Artificial Neural Network Potentials and DFT[END_REF] Still, these accurate potentials lack transferability and cannot be used directly to investigate how an adsorbate would be solvated or could react at this aqueous interface. Nevertheless, a system-specific machine-learning potential in combination with DFT resampling [START_REF] Jinnouchi | First-principles hydration free energies of oxygenated species at water-platinum interfaces[END_REF] allows to retrieve most of the solvent effects, albeit at a considerable computational cost. Furthermore, such schemes result in complex workflows, which require automatization in order to become viable for applications. [START_REF] Steinmann | Autonomous high-throughput computations in catalysis[END_REF] Reactive force fields are a good alternative to handle complex interfaces.

Once parameterized, they are fast enough to simulate 1 ns. For instance, ReaxFF has recently been used to investigate the dissociative adsorption and decomposition of acetic acid at the ZnO/water interface in function of the temperature. [START_REF] Sengul | ReaxFF Molecular Dynamics Study on the Influence of Temperature on Adsorption, Desorption, and Decomposition at the Acetic Acid/Water/ZnO(1010) Interface Enabling Cold Sintering[END_REF] Moreover, such simulations also give access to the entropy at the solid/water interface, [START_REF] Jung | Thermodynamic Description of Interfaces Applying the 2PT Method on ReaxFF Molecular Dynamics Simulations[END_REF] which will ultimately enable a fundamental understanding of the thermodynamic differences in reactivity between gas-phase, solution-phase and the water/solid interface.

Figure 1 :

 1 Figure 1: (a) Principle of the MMsolv method to compute adsorption energies at the water/solid interface (b) Gibbs free energy of adsorption of benzene at the Pt/water interface, simulation data from 43 and experimental data 45 (c) Snapshot of the Pt/water interface showing the first layer of hydration, extracted from MM simulations used in MMSolv.

61

 61

Figure 2 :

 2 Figure 2: Acetone hydrogenation on Ru(0001) and H 2 O-Ru(0001) studied using the PW91 functional. 56 (a) Energy profiles in eV (b) Optimized structures on Ru(0001) (c) Optimized structures on H 2 O-Ru(0001). Main distances are indicated in Å.

initio

  adsorption energies with solvation energies at the MM level. Compared with PCM, MMSolv accounts for the competitive adsorption of the water solvent without the arbitrariness of micro-solvation. Just like enhanced AIMD, MMSolv computes the properties CN(Al .;O of water) .;.O of alumina) α CN (Al.; O of water) α CN(Al..;.O of alumina) First and highest barrier 78 kJ.mol -1

Figure 3 :

 3 Figure 3: Exploration of the reactivity of γ-Al 2 O 3 (110) in contact with a slab of liquid water. 73 Top view (a) and side view (b) of the initial structure. Only chemisorbed water molecules are shown. O wat , O alumina , Al, H in blue, red, yellow, white respectively. Bidimensional free energy surfaces obtained from ab initio metadynamics when exploring the reactivity of the tetrahedral aluminum Al α (c) and Al β (d). Side view of the final structure (e) with a hydrated Al β extracted from the alumina network.

  gathers the energetic profile of acetone hydrogenation on Ru(0001) and on H 2 O-Ru(0001) with the related structures. In presence of a H-bonded water molecule on H 2 O-Ru(0001), acetone and iso-propanol are more strongly chemisorbed thanks to the additional H-bonding with the chemisorbed water. In contrast, the iso-propoxy intermediate is triggered to move from the hollow site to a bridge site that resembles more closely the transition state configuration. For this reason, water accelerates the ketone hydrogenation on oxophilic metals, where alkoxy intermediates are found to be particularly stable and difficult to hydrogenate into alcohols (O-H bond formation) or dehydrogenate into ketones (C-H bond scission).[START_REF] Michel | H versus O-H Bond Dissociation for Alcohols on a Rh(111) Surface: A Strong Assistance from Hydrogen Bonded Neighbors[END_REF][START_REF] Zaffran | Linear Energy Relations As Predictive Tools for Polyalcohol Catalytic Reactivity[END_REF][START_REF] Loffreda | Tuning catalytic reactivity on metal surfaces: Insights from DFT[END_REF][START_REF] Michel | Role of water on metal catalyst performance for ketone hydrogenation. A join experimental and theoretical study on levulinic acid conversion into gamma-valerolactone[END_REF] More recently, we have focused on the

energetics of O-H, C-H, C-C and C-O bonds cleavages of alcohols on Pt(111). Despite the strong polarity of O-H and C-O bonds, modeling water as a polarisable continuum

  This is how Siemer et al. 64 demonstrated that the O 2 bond cleavage barrier catalysed by Au 11 nanoparticule supported over TiO 2 is decreased by 25%

Acknowledgement

The authors thank all the collaborators and reviewers, as well as the funding agencies and private companies that have contributed to the development of the discussed advances in the understanding of aqueous interfaces.

Graphical TOC Entry

Solid/water interface


A New Methodological Approach to Analyze Human Roles in Human-Robot Interaction Scenarios

A. Puig-Pey 1 , A.Sanfeliu 1 , C. Leroux 2 , P. Dario 3 , R. Rasso 3 , B.C. Arrue 4 , P. Soueres 5 , F.Dailami 6 , V.Vasco 7 , M. Munih 8 , A. Ijspeert 9 Abstract-The influence of robotics in the job market has socio-economic consequences and the inevitable loss of job positions, but in the Human-Robot Interaction (HRI) scenarios, where humans and robots work together, new jobs and business models will be created. These HRI scenarios can be seen in manufacturing, medicine, maintenance, education, etc. and in the future, in most of the daily tasks. The purpose of this article is to analyze from the perspective of Human-Robot Interaction scenarios, which new HRI human roles and HRI tasks categories has to be taken into account. The new HRI human roles will serve to define and homogenize the transverse skills needed for workers working in HRI scenarios and for analyzing the human roles in robotic experiments. We introduce a methodological approach using the TERRINet HRI Template, which facilitates the analysis of tasks that in the near future will be done by humans working with robots. The Template has been used and tested in 20 study cases of HRI scenarios, validating the methodology and looking for homogenization in human roles.

I. INTRODUCTION

Robotic technology will be part of our the economic activity, improving the tasks that humans perform now and increasing the quality of human life and work. Robots are here to help and collaborate with humans creating a new system that will link the best of both. In this article we will refer to Human-Robot Interaction (HRI) scenarios, where humans and robots work together, although there could be a balance between full autonomy and pure tele-operation.

The human robot interaction literature points the consequences of the introduction of robotic technologies in the labor market and the consequences for human roles, which will lose part of the interesting tasks that they perform, for example, contact with customers [START_REF] Beane | What difference does a robot make? the material enactment of distributed coordination[END_REF], social acceptance or work comfort [START_REF] Mende | Service robots rising: How humanoids robots influence services experience and food consumption[END_REF]. The reason could be that the employees often do not have the right skills to learn new technologies and fail to understand the benefits of robotics, leading to confusion, resistance and decreasing trust on robots [START_REF] Lu | Service robots, customers and service employees: what can we learn from the academic literature and where are the gaps?[END_REF]. In the other hand, some literature defends that the introduction of a disruptive technology as the robotic and artificial intelligence (AI) one, could be a good opportunity to employers up skills, not only in soft skills [START_REF] Huang | Artificial intelligence in service[END_REF], but in technological and digital knowledge.

From these perspectives, it seems interesting to investigate the influence of robotics in the job market where human and robots work together, and analyzing the HRI tasks categories and roles that human will perform in specific robotic scenarios.

Coordinating social and technological analysis is not easy. The objectives are different, sometime complementary, the researchers belong to different knowledge areas and the conclusions pointed different audiences. These sociotechnological studies need specific methodology, including new procedures and a coordinated participation of different stakeholders [START_REF] Puig-Pey | Public entities driven robotic innovation in urban areas[END_REF]. In this article, a qualitative procedure inspired in Delphi methodology [START_REF] Pare | A systematic assessment of rigor in information systems ranking-type delphi studies[END_REF] is used to study and systematically approach the analysis of the human roles and tasks categories in future HRI scenarios, which will be used to validate the new proposed human roles and tasks and to look for homogenization of them in different scenarios.

In order to do this work, this article is structured in several sections. Section II makes a short state of the art. Section III presents the new methodlogical approach using the TERRINet HRI Template for analyzing human roles in HRI scenarios. Section IV analyze two study casesin Healthcare and Urban scenarios -using this Template. Section V extend this study to 20 study cases and presents some discussion of the analysis, and finally, section VI presents the conclusions.

This research article has been done in the framework of the TERRINet EU project (www.terrinet.eu), by the TERRINet's robotic teams of the infrastructures, under the coordination of the Universitat Politècnica de Catalunya (UPC).

II. STATE OF THE ART

Experts estimate that around half of today's work activities could be automated by 2055 [START_REF] Lu | Service robots, customers and service employees: what can we learn from the academic literature and where are the gaps?[END_REF]. The reason is that robotics and AI offer a wide range of potential benefits to organizations and can include cost reduction, productivity gains, enhanced reliability, scalability, improved compliance and security [START_REF] Wirtz | Brave new world: service robots in the frontline[END_REF]. These wide range of benefits has a counterpart in human workers and employers well-being. Along with other factors such as globalization, the introduction of new technologies has been found to change the jobs that are available and the skills those jobs require. Empirical studies demonstrate that digital technology -not robotic -has led to a decline in the relative demand for routine jobs in advanced economies [START_REF] Goos | Explaining job polarization: Routine-biased technological change and offshoring[END_REF].

A huge part of the literature reviewed on robotics and work forces is principally addressed to healthcare and hospitality services scenarios and mostly in social science publications, examining the impact of robots on services employers [START_REF] Lu | Service robots, customers and service employees: what can we learn from the academic literature and where are the gaps?[END_REF]; offering a huge analysis about the current state of Artificial Intelligence and Robots in technological trends, ethical questions and regulatory issues [START_REF] Royakkers | Just Ordinary Robots[END_REF]; analyzing customers' acceptance and end user responses [START_REF] Savela | Social acceptance of robots in different occupational fields: A systematic literature review[END_REF] or establishing the design of robots for good human acceptance [START_REF] Ivanov | Progress on robotics in hospitality and tourism: a review of the literature[END_REF].

With respect to the human roles and tasks in HRI scenarios several interesting articles addresses these issues.

Steinfeld [START_REF] Steinfeld | Common metrics for human-robot interaction[END_REF] introduced five task categories oriented to the work of humans with mobile robots. The tasks where selected because they can be performed with a high-level of human direction (pure tele-operation), a high-level of robot independence (full autonomy), or at any point on the interaction spectrum. Using these tasks they where able to define generic metrics that can be applied to a wide range of HRI scenarios and can be used to asses the impact of different levels or types if HRI on performance.

Another important work was published by Scholtz [START_REF] Scholtz | Theory and evaluation of human robot interactions[END_REF] who described the human roles in HRI scenarios. He made a precise description of each role, which allow to understand the interaction and collaboration between human and robot and open new possibilities about how to integrate the best of both capabilities.

Finally, from the perspective of evaluating HRI scenarios, the work of [START_REF] Yanco | Analysis of human-robot interaction at the darpa robotics challenge trials[END_REF] presents an analysis of the team performances in the field and control room at the DARPA robotic challenge trials.

III. THE TERRINET HRI TEMPLATE FOR ANALYZING

HUMAN ROLES IN HRI SCENARIOS As we have mentioned before, the aim of this article is to define a methodology to analyze the human roles and tasks categories in diverse robotic scenarios in order to understand which are the required human and robotic activities and also to look for the homogenization of roles among the scenarios. We have created a specific template, which is denominated TERRINet HRI template, that incorporates the basic information of the robotic tasks and the specific tasks that has to be done by each one of the involved human roles.

The TERRINet HRI template was elaborated through a set of rounds with robotic teams and end users, using a research methodology characterized by the analysis of the problem in its own context [START_REF] Yin | Discovering the future of the case study. method in evaluation research[END_REF], where the concepts are at the same time, the "inputs" and "outputs" of the research, and they are refined during the field work.

The first Template was structured in the following 4 sections:

• Current scenario description;

• Robotic scenario description and new operational procedure and activities; • HRI Tasks performed in each activity: navigation, perception, management, manipulation and social • HRI Roles: Supervisor, operator, mechanic, peer and bystander, In the first Template we used the same HRI tasks categories defined by Steinfeld [START_REF] Steinfeld | Common metrics for human-robot interaction[END_REF] and the same human roles defined by Scholtz [START_REF] Scholtz | Theory and evaluation of human robot interactions[END_REF].

We used this Template to analyze two different robotic scenarios: Robotic Geriatric Assessment [START_REF] Romero-Garcés | Towards a robust robotic assistant for comprehensive geriatric assessment procedures:updating the clarc system[END_REF], in the healthcare assistance scenario and Robotized Sewer Inspection [START_REF] Alejo | Siar: A ground robot solution for semi-autonomous inspection of visitable sewers[END_REF], in the urban surveillance and inspection scenario. After the first rounds with this Template in the two robotic scenarios working with the robotic team and the end users, we realized that these tasks and human roles where not enough. Then, we incorporated new tasks categories and human roles and we modified the Template. We used the new Template in 18 new scenarios, and again we introduced new modifications and finally we obtained the final version of the TERRINet HRI template that can be seen in Fig. 1.

The final Template expands the task categories in 6 categories: navigation, perception, management, manipulation, social and data management. The new task category is "Data management", which includes all the treatment of the data collected in the activity and treated in the Cloud Services.

With respect to the human roles, the final Template expand them in 9 categories: expert supervisor, technical supervisor, operator, mechanic, peer teammate, peer end user, bystander, trainer and mentor. These new human role categories allow us to incorporate new important human roles that were not considered previously.

IV. ANALYSIS OF TWO STUDY CASES USING THE TERRINET HRI TEMPLATE

In this section we analyzed two HRI scenarios: Robotic Geriatric Assessment [START_REF] Romero-Garcés | Towards a robust robotic assistant for comprehensive geriatric assessment procedures:updating the clarc system[END_REF], in the healthcare assistance scenario and Robotized Sewer Inspection [START_REF] Alejo | Siar: A ground robot solution for semi-autonomous inspection of visitable sewers[END_REF], in the urban surveillance and inspection. Fig. 2: Images of the Robotic Geriatric Assessment study case [START_REF] Romero-Garcés | Towards a robust robotic assistant for comprehensive geriatric assessment procedures:updating the clarc system[END_REF].

In both study cases, the analysis was done through a set of rounds by robotic teams and end users [START_REF] Varela | Public entity role in robotic innovation. barcelona participation in echord++ pdti project for urban challenges[END_REF].

A. HRI Tasks and Roles in Robotic Geriatric Assessment study case

The mission in this HRI scenario is to perform a Comprehensive Geriatric Assessment (CGA) test to the patients in a geriatric center. The project focuses on the development of a mobile robot able to receive the patient and its family, accompany them to the waiting room and then to the medical consulting room. At the waiting room, some robotic activities are performed, for example the registration data and tests and, once at the medical consulting room, the robot helps the physician to capture and manage the data of the Comprehensive Geriatric Assessment (CGA) procedures.

The activities of the new operational procedure using HRI tasks are (Fig. 2):

• Semi-autonomous tele-operated guiding and accompanying • Semi-autonomous tele-operated on line data acquisition • Off line clinician analysis, care planning and management. Not included in HRI tasks. • Operational procedure supervision • Robot maintenance, hardware and software updates The activities mentioned before were described through the group of HRI tasks categories defined in the Template.

In the rest of this section, we will describe the activities of each one of the HRI human roles for this specific study case, including the new human roles categories described before.

Supervisor. The analysis of this study case offers two different supervisor roles: expert and technical supervisor.

Expert supervisor: The current legislation in medical services, imposes to have a medical professional as the responsible of any medical action with patients and every procedure and task has to follow a specific protocol. This expert supervisor has a general information about the HRI robotic tasks: management, social and data management. The medical supervisor leads the preparation of all the procedures and checks the feedbacks of the human robot interaction (the relation between human and robot), and looks for improving or changing the current procedure and protocols. In this study case, the expert supervisor is a doctor or medical professional.

The Technical supervisor assists the medical supervisor, control the missions and proposes changes and improvements in the procedure. Moreover, he/she overview the situation, including progress of the multiple platforms -the mission or task plan -and the current behaviors of any of the robots including deviations that may require intervention. The technical supervisor should have deep knowledge about navigation, perception, management and data management HRI tasks and about the robots' characteristics, functionalities and specificity. A pilot license to control the robot is not mandatory if the supervisor won't tele-operate the robot. The technical supervisor could be a technician (that can include the operator role) or a healthcare professional with technical robotic knowledge.

Operator. In this case study the operator role must be a skilled user, having knowledge about navigation, perception, tele-operation, management, data management and social HRI tasks. Also the operator should have knowledge of the robot architecture and characteristics and the robot programming. A pilot license should be considered. The operator could tele-operate the robot or a group of robots in complex situations. The robot should be programmed before the execution of the task. A general overview of the state of robot could be done by the operator before the task starts, but normally the operator explains the problems to the technician that will do the periodic maintenance or repair.

Mechanic. This role includes hardware and software maintenance. It could be done by internal maintenance service or external one (a maintenance contract should be mandatory). It includes the mechanical, electronic and software settings of the robot. The mechanic should know the robots' characteristics, functionalities and specificity.

Peer. The analysis offers two different peer roles: peer teammate and peer end user.

In this specific study case, the Peer teammate is a healthcare professional (clinician-nurse) that will introduce the robot to the patient and his family. The peer teammate contributes to the team human-robot according to his ability, exhibiting social competences as interaction characteristics, persuasiveness, trust, engagement, including basic information about navigation, social and management. Any question or problem between robot and patient could be solved by him/her in short term.

The Peer end user is the patient. The patient and her/his family will establish a new relationship with the robot. This HRI human role should have information about the robotic scenario, the data management, the basic characteristics of the robot that will attend him/her and the social HRI tasks that the robot offers. The understanding of social communication and the designed interface are the key characteristics for a successful HRI.

Bystander. Along the guiding and accompanying activity, the robot will contact with diverse people at the corridors and waiting rooms. The bystander should know that the scenario includes robots and AI, the characteristics and behaviors of robots including the social HRI tasks. The creation of information tools as videos, posters and flyers could be advisable solutions for this human robot interaction stating.

Two new HRI roles -Expert supervisor and Peer end user -and a new HRI task -Data Management -have been detected in this scenario and included in the Template for Fig. 3: Images of the Sewer Inspection study case [START_REF] Alejo | Siar: A ground robot solution for semi-autonomous inspection of visitable sewers[END_REF]. the following analysis.

B. HRI Tasks and HRI Roles in Robotized Sewer Inspection study case

The mission in this HRI scenario is to inspect the sewer infrastructure using robots and a team workers. The current activities are performed by brigades that do inspection tasks 8 hours a day in the accessible sewer infrastructure (Fig. 3). The new operational procedure is a collaborative job between humans and robots to determine the state of the sewer by identifying the sewer segments where their functionalities have been reduced due to sediments or structural defects. The robot has to register images, videos and has to do geometric analysis (scanning). Additionally, the robot has to take samples of the water, air and sediments for monitoring them and do structural defect inspection. GIS cartography could be another functionality for those networks which do not have [START_REF] Puig-Pey | Public end-users driven technological innovation (pdti) in urban scenarios[END_REF].

The robotized sewer inspection' operational procedure includes: logistics; programming trials; inspection (video and images analysis); off line data analysis and management; operational procedure supervision; and robot maintenance. As we have done before, once we have described the HRI tasks to be performed in this new robotic scenario, we will analyze the human roles and the tasks involved in this scenario.

Supervisor. This role could join expert and technical supervision. In this activity is mandatory to have a procedure overview, to know the robot capacities, the tele-operation performance and the results of the full process aligned to the inspection requirements. The supervisor should know navigation, perception, management and data management HRI tasks in order to participate in the trials program and could do the off line data analysis and management. In Human-Robot Interactions the physical capabilities of the system change and the supervisor needs to know the "normal" status of the robot at any given time. The supervision operation will organize the process and check it in a continuous improving plan.

Operator. During the trials, the robot could go in autonomous mode or in tele-operated mode with remote interaction. In this case the operator will do tele-operation with knowledge in navigation, perception, manipulation, management and data management HRI tasks. This activity includes knowledge about the robot, sensors, and the robot plans. The management could include a team of robots that collaborate between them. The operator must be a skilled user, having knowledge of the robotic architecture and robotic programming. The operator should pilot the robot or Fig. 4: Table of the 20 study cases robots and should be capable of supporting interaction in a complex situation. The pilot license could be mandatory. This role shares information with the supervisor and vice versa.

Mechanic. This activity includes hardware and software maintenance. In these inspection scenarios were the trials could damage the robots, a technician, with robotic knowledge, could help the development of the operational procedure. As we have seen before, usually the robot will be sent to the manufacturer for any update or big repair.

Peer Teammate. This role includes knowledge about the robot navigation, operation and maintenance. It could be assumed by the operator. The current brigades could develop this role and could up skill their competences to perform the operator role.

As we have seen before, the robot maintenance includes hardware and software maintenance and could be done by an internal or external team.

V. HRI HUMAN ROLES IN ROBOTIZED SCENARIOS. 20

STUDY CASES We have analyzed 20 study cases that where prepared by the TERRINet partners in their infrastructures. These study cases can be seen in the table of Fig. 4.

For each one of these study cases we analyzed the HRI human roles and tasks. Fig. 5 shows the human roles for the diverse study cases. The human roles, expert and technical supervisor, operator, mechanic and peer teammate appear in almost all the cases, while the other roles appear occasionally.

We also analyzed what type of HRI task categories are required for each one of the human roles in all the study cases. Fig. 6 shows the analysis for healthcare assistance scenarios and Fig. 7 shows the analysis for the healthcare teleoperated interventions.

One of the important issues in the analysis of human roles, it is the study of which of the human roles can be homogenized among diverse scenarios or missions. In this research, Fig. 5: Analysis of human roles in the study cases Fig. 6: Analysis of tasks categories and human roles in healthcare assistance scenarios we realized that this is a very difficult topic, but in some cases we found that exist some type of homogenization. Fig. 8 shows that in the case of urban infrastructures inspection and maintenance scenarios, we can find homogenization of human roles trough common task categories.

In the analysis of the study cases, we discovered new HRI human roles, specifically in Healthcare Tele-operated Interventions scenario where the robot is fully operated by the medical or surgical professional, two new human roles were required: Mentor and Trainer.

Mentor is a counselor or guide expert that establishes a personal development relationship that helps a less experienced or less knowledgeable person. The mentor could be assimilated as an expert supervisor, but including tasks of Trainer is a person that prepares or trains people for the practice of a specific task. The robot manufacturer is who usually prepare this human role.

Other human roles appear besides the ones related with the HRI ones: robot designers (hardware and software); interface and communication designers; HRI trainers specifically for social tasks; and robotic set designers for each scenario where human and robots will interact and collaborate.

New business models will also appear linked to the robotic scenarios. For example, in last mile delivery use case, Small and Medium Companies (SMEs) could develop commercial solutions.

In all the HRI human roles, including the bystander, all people have to be prepared to work with robots or at least to know their characteristics and functionalities. Information

VI. CONCLUSIONS AND FUTURE RESEARCH PROPOSALS

In this article we have explained a new methodological approach to analyze Human-Robot Interaction scenarios. We have created a document that can help to do this process, which is denominated TERRINet HRI Template. This Template includes the description of the HRI task, the human roles and task categories. The Template uses 9 human roles to describe the activities: expert supervisor, technical supervisor, operator, mechanic (hardware and software), peer teammate, peer end user, bystander, mentor and trainer,. The Template also uses 6 HRI task categories: navigation, perception, manipulation, management, social and data management.

Using this template an methodological procedure, we have analyzed 20 study cases in diverse fields: healthcare assistance and teleoperated interventions; infrastructures maintenance and inspection; urban surveillance and logistics; drone teleoperation; education; agriculture vine branch pruning; military manipulation; and industrial co-workers.

For these study cases we could determine the human roles and their corresponding task categories. For the urban infrastructure maintenance and inspection, we have been able to find homogenization of the human roles.

Finally, this new methodologically approach can be extended to new HRI scenarios, where new human roles and task categories can be found. These new roles will imply new human abilities, new jobs, and new education and training for these jobs.

Fig. 1 :

 1 Fig. 1: The final version of the TERRINET HRI Template.

Fig. 7 :

 7 Fig. 7: Analysis of tasks categories and human roles in healthcare teleoperated interventions

Fig. 8 :

 8 Fig. 8: Scenarios where the homogenization of human roles among different missions can be done through common task categories

Work supported under the European project TERRINet (H2020-INFRAIA-2017-1-two-stage-730994) and the Spanish State Research Agency through the ROCOTRANSP project (PID2019-106702RB-C21 / AEI / 10.13039/501100011033))

The affiliation of authors is: 1 IRI (CSIC-UPC) Barcelona,