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Replacing fossil fuels with energy sources and carriers that are sustainable, environmentally benign, and affordable is amongst the most pressing challenges for future socio-economic development. To that goal, hydrogen is presumed to be the most promising energy carrier. Electrocatalytic water splitting, if driven by green electricity, would provide hydrogen with minimal CO2 footprint. The viability of water electrolysis still hinges on the availability of durable earth-abundant electrocatalyst materials and the overall process efficiency. This review spans from the fundamentals of electrocatalytically initiated water splitting to the very latest scientific findings from university and institutional research, also covering specifications and special features of the current industrial processes and those processes currently being tested in large-scale applications. Recently developed strategies are described for the optimisation and discovery of active and durable materials for electrodes that ever-increasingly harness first-principles calculations and machine learning. In addition, a technoeconomic analysis of water electrolysis is included that allows an assessment of the extent to which a large-scale implementation of water splitting can help to combat climate change. This review article is intended to cross-pollinate and strengthen efforts from fundamental understanding to technical implementation and to improve the ‘junctions’ between the field's physical chemists, materials scientists and engineers, as well as stimulate much-needed exchange among these groups on challenges encountered in the different domains.

Electrochemical reactions are usually thermally activated and submitted to mass-transfer effects. Although classically, enhanced kinetics of an electrochemical reaction is obtained by heating the cell and feeding the reactant by forced convection, other means can be used to improve mass-transfer and charge-transfer. This article shortly reviews the effects of magnetic fields in electrochemistry. Using a static or an alternating magnetic field enables to enhance electrodeposition and electrocatalysis, via improved gas and species convection, electrochemical kinetics, and whole reaction efficiency. Such enhancement can mainly be related to Lorentz and Kelvin forces, magneto-hydrodynamics, chiral-induced spin selectivity, and hyperthermia, these effects being described herein.

Hydrogen will be at the basis of the World’s energy policy in forthcoming decades, owing to its decarbonized nature, at least when produced from renewables. For now, hydrogen is still essentially produced from fossil feedstock (and to a minor extent from biomass); in consequence the present hydrogen gas on the market is containing non-negligible amounts of impurities that prevent its immediate usage in specialty chemistry or as an energy carrier in fuel cells, e.g. in transportation applications (cars, buses, trains, boats, etc.) that gradually spread on the planet. For these purposes, hydrogen must be of sufficient purity but also sufficiently compressed (at high pressures, typically 70 MPa), rendering purification and compression steps unavoidable in the hydrogen cycle. As shown in the first part of this contribution “Electrochemical hydrogen compression and purification versus competing technologies: Part I. pros and cons”, electrochemical hydrogen compressors (EHCs), which enable both hydrogen purification and compression, exhibit many theoretical (thermodynamic) and practical (kinetics) advantages over their mechanical counterparts. However, in order to be competitive, EHCs must operate in very intensive conditions (high current density and low cell voltage) that can only be reached if their core materials, e.g. the membrane and the electrodes/electrocatalysts, are optimized. This contribution will particularly focus on the properties electrocatalysts must exhibit to be used in EHCs: they shall promote (very) fast hydrogen oxidation reaction (HOR) in presence of impurities, which implies that they are (very) tolerant to poisons as well. This consists of a prerequisite for the operation of the anode of an EHC used for the purification-compression of hydrogen, and the materials developed for poison-tolerance in the vast literature on low-temperature fuel cells, may not always satisfy these two criteria, as this contribution will review.

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Today, hydrogen mainly originates from fossil sources (gas, oil, and coal). Room temperature water electrolysis is an interesting alternative for renewable electricity storage, even if it is well-known that high-temperature systems are more efficient. To address this issue, we studied different non-platinum group metal (non-PGM) catalysts for alkaline oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) by recording cyclic voltamperograms with a rotating disk electrode set up. Physicochemical characterizations of Ni-based and FeNi3-based catalysts were performed using transmission electron microscopy, X-ray diffraction (XRD), and inductively coupled plasma mass spectroscopy (ICP-MS). Ni synthesized by the hot injection method is a good catalyst for HER, yet still less active than Pt/C. FeNi3 with and without a Ni surface doping is very good OER catalysts, slightly better than commercial unsupported IrO2. Electrochemical tests under alternating magnetic field (AMF) using these nanoparticles are ongoing, as these materials are compatible with AMF activation.

Activity distribution limitation in electroactive biofilm remains an unclear phenomenon. Some observations using confocal microscopy have shown notable difference between activity close to the anode and activity at the liquid interface. A numerical model is developed in this work to describe biofilm growth and local biomass segregation in electroactive biofilm. Under our model hypothesis, metabolic activity distribution in the biofilm results from the competition between two limiting factors: acetate diffusion and electronic conduction in the biofilm. Influence of inactive biomass fraction (i.e. non-growing biomass fraction) properties (such as conductivity and density) is simulated to show variation in local biomass distribution. Introducing a dependence of effective diffusion to local density leads to a drastic biomass fraction segregation. Increasing density of inactive fraction reduces significantly acetate diffusion in biofilm, enhances biomass activity on the outer layer (liquid/biofilm interface) and maintains inner core largely inactive. High inactive fraction conductivity enhances biomass activity in the outer layer and enhances current production. Hence, investment in extracellular polymer substance (EPS), anchoring redox components, is benefit for biofilm electroactivity. However, under our model hypothesis it means that conductivity should be two order lower than biofilm conductivity reported in order to observe inner core active biomass segregation.

International audience; In this study, experimental results of hydrogen producing process based on anaerobic photosynthesis using the purple non-sulfur bacterium Rhodobacter capsulatus are scrutinized. The bacterial culture was carried out in aphoto-bioreactor operated in a quasi-continuous mode, using lactate as a carbon source. The method is based on the continuous stirred tank reactors (CSTR) technique to access kinetic parameters. The dynamic evolution of hydrogen production as a function of time was accurately simulated using Luedeking-Piret model and the growth of R. capsulatus was computed using Gompertz model. The combination of both models was successfully applied to determine the relevant parameters (λ, μ$_{max}$, α and β) for two R. capsulatus strains studied: the wild-type strain B10 and the H$_2$ over-producing mutant IR3. The mathematical description indicates that the photofermentation is more promising than dark fermentation for the conversion of organic substrates into biogas.

The water electrolysis appears as a sustainable solution for hydrogen production. The proton exchange membrane electrolyzers (PEM-E) play an increasingly important role in the development of hydrogen technology. Fast analysis of PEM-E efficiency using a mathematical approach is an effective tool for the improvement of these devices. This work presents a closed-form solution of single cell PEM-E modelling. The approach considers charge and mass transport balances. The one-dimensional study focuses on the anodic and the cathodic catalyst layer and the membrane using only dimensionless parameters. The analytical model allows to describe the water management as a function of pressure gradient and current density using a dimensionless ratio of water transport process ( β m , ). This model is endorsed by experimental data. Dimensionless parameters like Thiele modulus ( β a , c ) or Wagner number ( ω a , C ) are reached using numerical optimization methods. Changing values of dimensionless numbers, allow the observation of the impact of the two-phase flow regimes on the electrochemical performances.

Conventional Li-ion batteries contain flammable liquid based electrolytes that can leak and react violently with the environment leading to a fire.[1] A solution is to replace the liquid electrolyte by a Solid Polymer Electrolytes (SPEs). Indeed, SPEs are of interest thanks to their flexibility, process easiness, lack of volatile compounds, and chemical and electrochemical stability toward one the most promising anode material, i.e. Li metal.[2] Among the variety of SPEs reported in literature, Poly(ethylene oxide) (PEO) doped with a Li salt is the most studied polymer electrolyte.[3] Indeed, PEO contains ether coordination sites that efficiently dissociate Li salts and its flexible macromolecular backbone enables ionic transport. Ionic conduction in SPEs depends for a large part on the dynamics of the polymer chains (ref. Devaux et al. SSI 2012). Therefore, a fine understanding of the relationship between polymer chain conformation and ionic conductivity is necessary to pave the way toward an optimized SPE. The goal being to produce a SPE suitable for a Li metal battery operating at room temperature. In this study, we report first on a setup designed to stretch SPE coupled with impedance spectroscopy in controlled Argon atmosphere. As an example, Figure 1 shows the impedance spectra under Argon at room temperature of a SPE made of high molecular weight PEO laden with LiTFSI (EO:Li =25) at different elongations (ε). Then, in-plane and through-plane conductivity of SPEs have been compared. 3 different type of SPEs has been studied of i) reference PEO/LiTFSI, ii) block copolymer electrolyte comprising polystyrene and PEO blocks (ref. Bouchet et al, Macromolecules 2014), and iii) composite electrolytes where PEO or the block copolymer is mixed with inorganic particles. References [1] D. Lisbona, T. Snee, Process Saf. Environ., 89 (2011) 434. [2] W. Xu et al., Energy Environ. Sci., 7 (2014) 513. [3] R C. Agrawal, G. P. Pandey, J. Phys, D, 41 (2008) 223001. Figure 1

International audience; Direct Numerical Simulations of a laminar two-phase flow into a vertical channel are investigated. An Eulerian–Lagrangian approach allows tracking each bubble position with a four-way coupling strategy, i.e. taking into account bubble-fluid and bubble-bubble interactions. The flow configuration has been chosen to highlight the buoyancy effects due to significant values of void fraction (high numbers of bubbles); hence the bubbles collisions and wall effects are the critical parameters to ensure the dispersion of the bubble plume. The DNS approach is self-consistent and does not rely on closure relations or empirical correlations for describing the collective bubble dynamics. It is found that the DNS predicts well the behavior of the bubble plume and its back effect on the liquid phase when compared with a mixture model and experimental data. The elastic nature of collisions, the sensitivity of the mean and RMS values of velocities and void fraction to the mesh quality are explored.

It is undisputed that hydrogen will play a great role in our future energetic mix, because it enables the storage of renewable electricity (power-to-H2) and the reversible conversion into electricity in fuel cell, not to speak of its wide use in the (petro)chemical industry. Whereas in these applications, pure hydrogen is required, today's hydrogen production is still largely based on fossil fuels and can therefore not be considered pure. Therefore, purification of hydrogen is mandatory, at a large scale. In addition, hydrogen being the lightest gas, its volumetric energy content is well-below its competing fuels, unless it is compressed at high pressures (typically 70 MPa), making compression unavoidable as well. This contribution will detail the means available today for both purification and for compression of hydrogen. It will show that among the available technologies, the electrochemical hydrogen compressor (EHC), which also enables hydrogen purification, has numerous advantages compared to the classical technologies currently used at the industrial scale. EHC has their thermodynamic and operational advantages, but also their ease of use. However, the deployment of EHCs will be viable only if they reach sufficient performances, which implies some specifications that their base materials should stick to. The present contribution will detail these specifications.

The hydrogen production by SOECs coupled with renewable energy sources is a promising route for the sustainability hydrogen economy. Multiphysics computing simulations appear to be the most efficient approaches to analyze the coupled mechanisms of SOEC operation. Using a relevant model, it is possible to predict the electrical behavior of solid oxide electrodes considering the current collector design. The influences of diffusion and grain diameter on cell performances can be investigated through 2D simulations, current–voltage characteristics, and current source distribution through electrodes. The simulation results emphasize that diffusion is linked to a relocation of the reaction away from the interface electrolyte/electrode, in the volume of the cathode. Furthermore, the current collector proves itself to be a great obstacle to gas access, inducing underneath it a shortage of steam. Inducing gradients of grain diameters in both anode and cathode drives the current sources to occur close to the electrode/electrolyte interface, thus decreasing ohmic losses and facilitating gas access. This approach shows the crucial importance of cathode microstructure as this electrode controls the cell response.

Hydrogen is one of the leading candidates in the search for an alternative to fossil hydrocarbon fuels. The spread of these technologies requires a real-time control of generator performances. Artificial intelligence (AI) and mathematic tools can make smarter the smart grid. The electrochemical modeling can be coupled successfully with artificial intelligent approach, if these models can be quickly computed with a large numerical stability. This chapter shows a methodology to build this kind of modeling work. Thanks to a simplified but physically reasonable model of PEM fuel cell, we will show that the reactant access (oxygen) or water management (a product of the reaction) and the reaction rate can be easily described with low computing time consuming. In addition, the artificial neural network could be trained with a reduced amount of data generated by these cell models.

This work focuses on the segregation of microbial populations in Electrochemically Active Biofilms (EAB) fed by glucose under continuous flow, simulated with a 2D bioanode model. In the model several reactions take place in parallel (fermentation, electroactivity, methanogenesis), performed by four microbial metabolic groups. Bioconversion yields and rate parameters were estimated by a thermodynamic approach. The model results include biomass segregation according to metabolic activity, distribution of concentrations of solutes and current production along the anode. This numerical tool exhibits an acceptable numerical cost (7000 nodes and below 35,000 degrees of freedom) to evaluate innovative designs for enhancing the bioelectrochemical reactor efficiency using a multicriteria approach. Therefore, a multi-objective optimization (coulombic efficiencies and organic removal rates) was achieved and highlights a Pareto front, showing that relatively high coulombic efficiencies (60–70%) can be obtained with a high removal rate ranging from 0.3 to 0.5 g COD cm−3 d−1.

Environmental concerns are generating a growing interest of the hydrogen sources, however hydrogen exhibits critical storage barriers. The production of pressurized biohydrogen would facilitate the gas storage and make it economically viable. In this work, Rhodobacter capsulatus in a closed photosynthetic reactor exhibited the ability to produce hydrogen to a pressure of 8.25 bars. The amount of hydrogen produced from synthetic media (lactate (35 mmol L−1) and glutamate (5 mmol L−1)) in a closed vessel was 1.8 times that obtained in a vessel open to the atmosphere. Hydrogen purity surpassed 90% with a lactate conversion rate of up to 70%. Influences of buffer composition in synthetic media and the illumination process (white LED or Na-lamp) are discussed. Moreover, pressurized hydrogen was successfully produced from a complex real effluent containing organic acids (lactate and acetate) generated by an initial dark biofermentation of hydrolyzed wheat straw. Therefore, under pressurized conditions, the stress increases the energetic demand and improves hydrogen production (survival vs growth). The energetic gain of the direct compression of biohydrogen d is equal to 1.3 kWh/kg H2.

International audience; This work focuses on a signal-based diagnosis approach dedicated to proton exchange membrane water electrolyzer (PEM WE) anode pump fault. The PEM WE cell measurements are performed with an experimental test bench to highlight the impact of water flow rate in the anode compartment. This approach is non-intrusive, and it can detect anode flow rate variation during the electrolysis and is designed to fulfill online diagnosis requirements. Contrary to electrochemical impedance spectroscopy-based approaches (EIS), this method stands out from existing procedures as a result of its few requirements, excluding any signal with perturbing amplitude. Therefore, the electrolyzer remains continuously available, even while the analysis is performed. The empirical mode decomposition (EMD) is used to decompose the signal variation into a sum of amplitude modulation and frequency modulation (AM-FM) components, called intrinsic mode functions (IMFs). In this work, the PEM WE current signal is decomposed into several IMFs using EMD. Then, the energetic contribution of each IMF is calculated. Experimental results exhibited that the energetic contribution of IMFs can be used as relevant criteria for fault diagnosis in PEM WE systems. This process only requires monitoring of the PEM WE current and has a low computational cost, which is a significant economic and technical advantage.

The water electrolysis based on Polymeric Electrolyte Membrane technology (E-PEM) is an interesting solution for efficient carbon-free hydrogen production. By the end of the 21st century, the contribution of hydrogen will continue to achieve significant rate in the energy mix. As there have been advances of efficient end-use technologies, hydrogen could even become the main energy carrier [1]. Regarding diagnosis purposes, Empirical Model Decomposition (EMD) method has proven to be a versatile and efficient tool to analyze non-stationary signals and extract features from them [2]. As a starting point of its decomposition, oscillations are considered, at a local level, as the sum of a specified number of high and low frequency contributions called Intrinsic Mode Functions (IMFs). IMFs represent the natural oscillatory mode embedded in the signal and work as the basis functions, which makes EMD a self-adaptive method. fig.1 shows the decomposition of the E-PEM current into a finite set of intrinsic mode functions. This study presents a non-intrusive tool designed to fulfill on-line diagnosis requirements. Indeed, the proposed method does not require any excitation signal or stabilization period as Electrochemical Impedance Spectroscopy-based approaches [3]. Therefore, the electrolyzer remains continuously available, even while the diagnosis is being performed. Besides, it only requires measurement of current and has a low computational costs, which are significant economic and technical advantages. Here, EMD has been used to study the anode flow rate dynamics. Several experiments have been conducted and experimental results have demonstrated the effectiveness of the proposed diagnosis tool and its advantages compared to other methods. Acknowledgements This project has received funding from the Reunion Island Region and the European Commission – ERDF References Barbir, “PEM electrolysis for production of hydrogen from renewable energy sources,” Solar Energy, vol. 78, no. 5, pp. 661–669, May 2005, doi: 10.1016/j.solener.2004.09.003. Damour, M. Benne, B. Grondin-Perez, M. Bessafi, D. Hissel, and J.-P. Chabriat, “Polymer electrolyte membrane fuel cell fault diagnosis based on empirical mode decomposition,” Journal of Power Sources, vol. 299, pp. 596–603, Dec. 2015, doi: 10.1016/j.jpowsour.2015.09.041. C. Garcia-Navarro, M. Schulze, and K. A. Friedrich, “Measuring and modeling mass transport losses in proton exchange membrane water electrolyzers using electrochemical impedance spectroscopy,” Journal of Power Sources, vol. 431, pp. 189–204, Aug. 2019, doi: 10.1016/j.jpowsour.2019.05.027. Figure 1: Intrinsic mode functions decomposition for operating conditions of 1.6 V and 0.5 ml.min-1 Figure 1

Decoupling water electrolysis using mediator is an interesting way to produce pure hydrogen. The present work validates the proof of concept of decoupled electrolyser associated with a bioelectrochemical system (MFC-DES) through a redox flow mediator (potassium hexacyanoferrate (KHCF)). Low voltage (1 V) hydrogen production was achieved with a current density up to 25 mA cm−2. Regeneration of the mediator was performed by glucose fed microbial fuel cells. The oxidation rate of KHCF in the electrolyser is, at least, an order of magnitude higher than the reduction rate in MFC cascade fed system. MFC-DES is thus a promising set up as it desynchronizes limited microbial rate and hydrogen production, generate value from wastewater and reduce energetic cost of water electrolysis.

Water electrolysis enables the storage of renewable electricity via the chemical bonds of hydrogen. However, proton-exchange-membrane electrolysers are impeded by the high cost and low availability of their noble-metal electrocatalysts, whereas alkaline electrolysers operate at a low power density. Here, we demonstrate that electrocatalytic reactions relevant for water splitting can be improved by employing magnetic heating of noble-metal-free catalysts. Using nickel-coated iron carbide nanoparticles, which are prone to magnetic heating under high-frequency alternating magnetic fields, the overpotential (at 20 mA cm−2) required for oxygen evolution in an alkaline water-electrolysis flow-cell was decreased by 200 mV and that for hydrogen evolution was decreased by 100 mV. This enhancement of oxygen-evolution kinetics is equivalent to a rise of the cell temperature to ~200 °C, but in practice it increased by 5 °C only. This work suggests that, in the future, water splitting near the equilibrium voltage could be possible at room temperature, which is currently beyond reach in the classic approach to water electrolysis. Electrocatalytic water splitting to produce H2 is impeded by slow reaction kinetics over noble-metal-free catalysts at the electrodes. Here, the authors use high-frequency alternating magnetic fields to locally heat FeC–Ni core–shell catalysts, enhancing the kinetics of the oxygen and hydrogen evolution reactions.

Based on proton conduction of polymeric electrolyte membrane (PEM) technology, the Polymer Electrolyte Membrane Water Electrolyser (PEMWE) offers an interesting solution for efficient hydrogen production. During the electrolysis of water in PEMWE, water is split into oxygen, protons and electrons at the anode and a water-gas two-phase flow results. The aim of this study is to investigate the link between the two-phase flow at the anode side and cell performance under low-pressure conditions. We have developed a two-dimensional stationary PEMWE model that takes into account electrochemical reaction, heat transfer, mass transfer (bubble flow) and charge balance through the Membrane Electrodes Assembly (MEA). In order to take into account the changing electrical behaviour, our model combines two scales of descriptions: at microscale within anodic active layer and MEA scale. The water management at both scales is strongly linked to the Not Coalesced Bubble regime (NCB regime) or the Coalesced Bubble regime (CB regime). Therefore, water content close to active surface areas depends on two-phase flow regimes. Our simulation results demonstrate that the coalesced phenomenon is associated with improvement of mass transfer, a decrease in ohmic resistance and an enhancement of the PEMWE efficiency. At low and medium current density values, the model has been validated using two separate experiment electrolysis cells.

International audience; In this work, a fast nonlinear model-based predictive control (NMPC) strategy is designed and experimentally validated on-line on a real fuel cell. Regarding NMPC strategies, the most challenging part remains to achieve on-line implementation, especially when dealing with fast dynamic systems. As previously demonstrated in a recent work, the proposed control strategy is ideally suited to address this problem. Indeed, it is 30 times faster than classical NMPC controllers. This strategy relies on a specific parameterization of the control actions to reduce the computational time and achieve on-line implementation. Due to its short computational time compared to mechanistic models, an artificial neural network model is designed and experimentally validated. This model is employed as internal model in the NMPC controller to predict the system behavior. To confirm the applicability and the relevance of the proposed NMPC controller varying control scenarios are investigated on a test bench. The built-in controller is overridden and the NMPC controller is implemented externally and executed on-line. Experimental results exhibit the outstanding tracking capability and robustness against model-process mismatch of the proposed strategy. The parameterized NMPC controller turns out to be an excellent candidate for on-line applications.

International audience; Spent fuel reprocessing and notably plutonium recycling contributes in enhancing the sustainability of nuclear energy by preserving uranium natural resources and decreasing the long term radiotoxicity of the final waste. After initial dissolution of the spent nuclear fuel in nitric acid, uranium and plutonium recovery from ultimate waste (fission products and minor actinides) is operated by a liquid liquid extraction process (PUREX process) and plutonium partitioning from uranium is run on the basis of the selective reduction of Pu and its back extraction. Therefore, the redox properties of Pu in nitric acid are of prime importance and the stabilization of Pu at its lower redox state + III is to be mastered. This study then deals with the characterization of Pu(IV)/Pu(III) redox couple in aqueous nitric acid solution. It was aimed at measuring physico-chemical features of the redox couple such as half-wave and conditional standard potentials, diffusion coefficients and charge transfer rate constant in nitric acid medium. These features have been used in modeling experimental results of preparative Pu(IV) reduction tests in nitrate medium in a laboratory parallel plate electrode cell.

Classical solid oxide fuel cell anode (Ni–cermet) could be employed as solid oxide electrolysis cell cathode. Ni–cermet has been synthesized and tested as solid oxide electrolyzer cathode using three-electrode techniques between 700 °C and 900 °C. yttria stabilized zirconia was used as the electrolyte and Pt as the counter electrode. Polarization curves and impedance spectra have been analyzed for two gas compositions. The presented results demonstrated an influence of Ni–cermet electrode behavior upon gas composition and temperature. The present results highlight a mechanism changing on Ni–cermet electrode upon gas composition. In a second part, a one-dimensional steady state model is developed to predict the cathodic behavior of Ni–cermet. This model takes into account mass and charge conservation, transport of species and reaction kinetics. It considers the porous electrode to be a homogeneous medium characterized. The influence of varying chemical and electrochemical steps kinetic on the shape of polarization curves is discussed. At high overpotential values the model with two rate-limiting steps has been validated using numerical optimization method.

A one-dimensional model has been developed to model the mass and charge transfer occurring in the water reduction on nickel-cermet. An artificial neural network (ANN) was identified and validated from this model. The ANN, in equation form, was used in a three-dimensional model of a serial repeat unit of a Solid Oxide Electrolysis Cell stack. The electrochemical processes can be modeled with acceptable accuracy with the one-dimensional model based on a two-step mechanism for the water reduction. The presented results show that the ANN could be employed to model electrochemical reactions and be implemented in a macro-scale model.

Satisfactory power densities for Single Chamber Solid Oxide Fuel Cells (SC-SOFC) can be obtained with ceramic materials already used in dual chambers SOFC. In order to increase the oxygen access trough the cathode, the authors propose to combine a SC-SOFC and a dual chamber SOFC by using a porous ceramic membrane. In this computing work, species transport is governed by convection-diffusion equations in the gas channel and the porous media. In addition, momentum balances are solved using Brinkman formulation through the porous cell. Charge transfer occurs at the electrode/electrolyte interface and is described by the general Butler-Volmer equation. Simulations allow the calculation of the distributions of partial pressures for all the gas species within the cell (CH4, H2, CO, CO2, H2O, O2, N2). As expected, the injection of only 3% of the steam water increases the chemical conversion of methane.

The development of solid oxide fuel cells has reached a new stage with intermediate temperature SOFCs. The protonic ceramic fuel cell is fundamentally different because it relies on proton conductivity through the electrolyte and not oxygen ions like SOFCs. Only few experimental results on PCFC are reported in literature compare to SOFC devices. The present work deals with three-dimensional geometry in steady state conditions and the role of interconnect for circular PEN PCFC is investigated. The gas flow inlet is at the centre of the cell. It is impossible to consider the problem using only two directions due to symmetry plan absence. To overcome the difficulty of high memory capacity required for 3D simulations, axes make it possible to consider only an eighth part of this configuration The present study reveals a strong edge effects to collect the current and a limiting access of oxygen due to water production.

Ni-Cermet and LSM were synthesized and tested respectively as solid oxide electrolyser cathode and anode using three-electrode techniques between 973K and 1173K. YSZ was used as the electrolyte and Pt as the counter electrode. Polarization curves and impedance spectra have been analyzed for different gas compositions. The present results highlight a mechanism changing on Ni-cermet electrode upon gas composition. Oxygen ion oxidation on LSM electrode should be described using a Tafel's law depending on oxygen concentration. Moreover resistance polarization electrode exhibits a same magnitude order for LSM electrode as for Ni-YSZ cermet electrode.

A model of a singular cell of an anode support SOEC is proposed in this work. The results of simulations will allow us to understand and to analyze the ionic and electronic ohmic drops effects on the cell performances. This paper proposes a model solution using the CFD-Ace+ software package to simulate the behaviour of this tubular SOEC. Modelling is based on solving conservation equations of mass, momentum, energy, species and electric current by using a finite volume approach on 3D grids of arbitrary topology. The electrochemistry in porous electrodes is described using Butler-Volmer equations at the triple phase boundary. The layout in 3D of the current densities, the electronic and ionic potentials allow the analysis of the respective ohmic drops. The simulation results emphasize the critical behaviour of SOEC such as the endothermic, exothermic and thermo-neutral operating mode.

This work is devoted to the modeling of two phase flows arising in typical electrolysis devices. A numerical mixture model is used in order to resolve the two dimensional bubble plumes evolving along the electrodes. Plumes thickness sensitivity is studied for various parameters, such as bubble diameter, electrolyte viscosity, electrochemical cell geometry and current density. Using thermal buoyancy driven flow analogy, a dimensionless Rayleigh-like number R α f , e is defined to predict the behavior of the wall-bounded gas convection between two vertical facing electrodes. Different bubbles dispersion mechanisms are observed depending on two-phase flow dynamics and physical properties of the mixture. The effect of forced convection in the channel is also investigated. A scaling law for plume thickness evolution for a large range of Prandtl-equivalent number values is proposed. These results show that the bubble plume can be efficiently controlled by an imposed electrolyte velocity.

Solid oxide fuel cell (SOFC) optimization requires detailed analysis based on both, experimental and simulated data. In the first part of this work, a review of anode models is presented. The various approaches, the considered parameters and the calculated data are analyzed. In the second part, a computer program model of a SOFC running with methane steam reforming within the anode is presented, based on a kinetic approach. First results are given and discussed.

International audience; This work investigates the mass transfer of the Airborne Molecular cross Contamination (AMCs) between the Front Opening Unified Pod (FOUP) and wafer (silicon substrates) during the microelectronics devices manufacturing using dynamic boundary conditions. Such cross-contamination phenomena lead to detrimental impact on production yield in microelectronic industry and a predictive approach using modelling and computational methods is a very strong way to understand and qualify the AMCs cross contamination processes. The FOUP is made of polymeric materials and it is considered as a heterogeneous porous media, it can adsorb and desorb the contaminant, thus the modelled processes are the contamination of two-component in transient flow. Coupled diffusion and convection-diffusion model with heat effects are used to define the phenomena. The present methodology is, first using the optimization methods with the numerical solution in order to define the physical constants of various materials which have been studied experimentally and separately, and the second using the finite element methods including these physical constants and relevant interface condition in order to take into account the adsorption kinetics law. Numerical methods to solve the problem are proposed. The dynamics behaviour of the AMCs analysis was determined thanks to the switch of Dirichlet to Neumann condition. The mathematical model preserves the classical forms of the diffusion and convection diffusion equations and yields to consistent form of the Fick's law. The computed results are in correlation with the experimental measurements. Some numerical results are presented in this work.

International audience; This paper deals a predictive model using modeling and computational methods to investigate the sensitivity of some materials constituents of the FOUP with the AMCs cross contamination. Required numerical tools which are employed in order to study the AMCs cross-contamination transfer phenomena between wafers and FOUPs were developed. Numerical optimization and finite elements formulation in transient analysis were established. Analytical solution of one dimensional problem was developed and the calibration process of physical constants was performed. This mode was used to study the sensitivity of some material with the cross contamination. The behavior of the AMCs in transient analysis was determined. The model framework preserves the classical forms of the diffusion and convection-diffusion equations and yields to consistent form of the Fick's law. The adsorption kinetics of the contaminant on the surface (interface contaminant/polymer) was assumed. The adsorption process and the surface roughness effect were also traduced as a boundary condition using the switch condition Dirichlet to Neumann and the interface condition. Many tests of contamination processes were assumed in order to study the sensitivity of the materials. Optimization methods with analytical solution were used to define physical constants for each material versus contaminant. Finite element methods including adsorption kinetic were also used and by using Henry law on the interface and the switch of Dirichlet to Neumann conditions.

International audience; This paper proposes a real-time implementable self-tuning PID control strategy to tackle oxygen excess ratio regulation challenge of a proton exchange membrane fuel cell. Controller parameters are updated on-line, at each sampling time, using a not iterative procedure based on an artificial neural network model. The proposed controller takes account of nonlinear behaviors of the process, while avoiding heavy computations. To assess the efficiency and relevance of the proposed strategy, the controller is implemented on-line, experimentally validated on a real fuel cell and compared to the built-in controller. In this aim, several control scenarios are considered to evaluate the controller performance. Experimental results show the excellent tracking capability and disturbances rejection ability of the controller, regardless of the operating conditions. Moreover, compared to the built-in controller the proposed strategy demonstrates better disturbances rejection capability. Overall, the proposed neural model-based self-tuning PID controller appears as an excellent candidate to address the oxygen excess ratio regulation issue.

International audience; This work highlights the gains of an innovative model-based control approach applied to a proton exchange membrane fuel cell (PEMFC) system, included in a stand-alone hybrid generator. This approach proposes a multivariable setpoint tracking of the PEMFC output power and temperature. The freshness of this approach is based on the combination of a nonlinear model-based predictive control strategy (NMPC) and a global linearizing control (GLC) algorithm. The performance of the proposed control strategy is confirmed thanks to simulations of varying control scenarios. Results show good performance in setpoint tracking, disturbances rejection and robustness against plant/model mismatch in presence of noisy signals. Moreover, for similar setpoint point tracking accuracy, the proposed control strategy appears to be four times faster than a classical multivariable NMPC strategy. According to real-time application objectives, this control strategy appears as a promising option to be implanted in the overall control scheme of the stand-alone hybrid power generator.

International audience; A 2D multi-physic in-house-model has been developed to analyse the performances of Solid Oxide Electrolysis Cell (SOEC) stack This model encompasses a combined electrochemical and thermal description of the electrolyser An analytical solution for multi-species diffusion across the porous cathode has been implemented in the model This numerical tool is useful to provide all the important parameters of the stack operation distribution of temperature heat fluxes local current densities gas concentrations and overpotentials Simulations show that thermal equilibrium of the stack is strongly dependant on radiative heat losses whereas convective heat transfers are limited In the exothermic operation mode the cell warming depends on the radiation efficiency A parametric study has been carried out to analyse SOEC irreversible losses It is found that the anode activation overpotential is significant whereas the polarisation due to the cathode activation remains much more limited Anode concentration overpotentials are found to be insignificant whatever the operating condition Cathode concentration overpotentials are found to be moderate in the case of Electrolyte Supported Cell (ESC) while they can increase drastically with current density in the case of Cathode Supported Cell (CSC) Addition of diluent gases into the H(2) H(2)O mixture is found to increase the concentration overpotentials

International audience; The effect of cathodic activation of sprayed La0.8Sr0.2MnO3 (LSM) films has been studied by electrochemical spectroscopy impedance (EIS). LSM powder was prepared by a citrate route and X-ray diffraction analyses show a complete LSM crystallization without La2O3 or La(OH)3 as side products. Porosity and grain size estimated from scanning electronic microscopy gave values of 33% and 100 nm, respectively. EIS measurement was performed on a Pt/yttria-stabilized zirconia/LSM cell before and after a cathodic current load (300 mA/cm2) on LSM electrode. The relaxation process, which is time-dependent, has been investigated. A drastic decrease of the electrode resistance was noticed just after applying the cathodic current, but after 9 h at optimized valence configuration in air at 850 °C, the recorded polarization resistance gradually enhanced until it almost reached the initial value. The resulting diagrams have been fitted using a Gerischer associated with a resistor and constant phase elements. This simple method has permitted us to observe that only the electrode interfaces are modified by a cathodic activation and the microstructure remains nearly constant.

International audience; Large PEM cells will be used in future proton exchange membrane fuel cell (PEMFC) power plants and appropriate tools are therefore be needed to study their behaviour. One approach to understanding single cell behaviour involves using mathematical models. The numerous techniques used in this work to describe PEM electrode behaviour require different scientific disciplines: chemical engineering and electrochemistry. This study proposes combining residence time distribution (RTD) and electrochemical impedance spectroscopy (EIS). The investigation focuses on cathodic DC and AC responses where over-voltage is critical. Results demonstrate that although gas distribution does not cause additional loops on impedance diagrams, it is strongly related to both the shape and amplitude of these diagrams. The simulations have drawn attention to operating conditions that can threaten the life of the PEM cell: under these setting points EIS method is not sufficient to detect this risk.

The aim of this work is to optimize an interconnect design. A three-dimensional model have been developed in order to investigate the effect of interconnect design on electrical performance and degradation process. Oxygen concentration, potential, current density and temperature distribution in interconnect and SOFC cathode have been calculated. Cathode degradation has been supposed to be due to temperature gradient non-uniformity. Our studies have demonstrated the impact of cathode/interconnect contact on thermal and electrical behavior. Thus, an optimization of the cathode/interconnect contact using COMSOL Multiphysics ® software has been investigated. In this investigation, the effects of the two geometrical parameters are considered. This paper presents the modification of cathode/interconnect contact area and electrical collecting pins size. Simulations show a decreasing power density and a reduction of temperature gradient for an increasing contact area. With a decreasing size of collecting pins, better temperature homogeneity and power density are recorded.

Fuel cells are highly efficient in terms of energy production, due to their high power efficiency. Solid Oxide Fuel Cells or Protonic Ceramic Fuel Cell are often proposed. The present paper aims to report on the electrochemical performance comparison between both systems by a Computational Fluid Dynamics approach. The developed model consists of mass, energy balances, and an electrochemical model that relates the fuel, air gas composition and temperature to voltage, current density, and other relevant fuel cell parameters. The electrochemical performances of SOFCs and PCFCs are analysed for several flow contigurations. The simulations show that, the flow management should be an essential key during the design optimization. In the PCFC operating conditions, steam is produced at the cathodic side and an excessive steam can involve clogging of PCFC cathode. As a result, electrochemical performance of PCFCs decreases more than SOFCs executions.

Electrochemical systems that could be employed with reversible functions has been developed: electric production in a solid oxide fuel cell (SOFC) mode and hydrogen production in a solid oxide electrolysis cell (SOEC). This paper proposes a model solution using the CFD-Ace software package to simulate the behaviour of a tubular SOEC. Modelling is based on solving conservation equations of mass, momentum, energy, species and electric current by using a finite volume approach on 3D grids of arbitrary topology. The electrochemical behaviour of porous electrode is described using Butler-Volmer equations at triple phase boundaries. The 3D layouts of the current densities, electronic and ionic potentials allow the analysis of the respective ohmic drops. Simulations indicate that the principal damaging risks at the electrolyte/anode interface originate from high flux densities of oxygen and from the possible re-oxidation of cermet-based cathode.

International audience; A composite electrode comprising a porous mixture of solid electrolyte (typically yttria stabilized zirconia, YSZ) and electronically conducting, electrocatalytic material (typically strontium doped lanthanum manganite, LSM) is generally used to improve the cathodic performance of the solid oxide fuel cell (SOFC). The advantage of the composite electrode is that the reaction zone is spread from the electrode/electrolyte interface into the electrode, effectively resulting in a functionally diffuse interface where the charge transfer reaction occurs. The present study proposes a one-dimensional dc and ac model that takes into account mass and charge conservation, transport of species and reaction kinetics. It considers the porous electrode to be a homogeneous medium characterized by a number of parameters, and in particular ionic conductivity and the diffusion coefficient. The influence of kinetic and transport parameters as well as that of the microstructure on the shape of both polarization curves and impedance diagrams is discussed.

International audience; The aim of this study is the understanding of the main phenomena governing fuel cell performances. We present a fuel cell model that takes into account gas diffusion in the porous electrodes, water diffusion and electro-osmotic transport through the polymeric membrane, and heat transfer in both the Membrane Electrodes Assembly (MEA) and bipolar plates. This model is constructed by combining independent descriptions of heat and mass transfers in the cell with a third description of coupled charge and mass transfers in the electrodes, considered porous. The results show that thermal gradients in the MEA could lead to thermal stresses at high current densities. The feeding gas temperature influence on the cell temperature is also important.

International audience; Theoretical calculations and experimental results have clearly demonstrated that a composite electrode should exhibit low activation polarisation by spreading the electrochemical active area within the volume of the electrode. The present modelling has been performed in order to give a complete description of such an electrode structure as well as the processes occurring therein. A one-dimension flooded homogeneous model and a microscopic approach were used. The cathode was assumed to be composed of spherical particles of ionic (YSZ) and electronic conductors (M). The porous mixture of spherical grains was described as a face-centred cubic lattice. The microstructural parameters of interest include: the electrode thickness (L), the grain diameter (dYSZ = dM = dg), the porosity (ε), the specific adsorption surface area (avads), the specific electrochemical surface area (avtpb), the pore diameter (dp) and the composition (εa). The proposed approach defines three independent parameters: ε, dg and εa. For a given electrode composition, the results suggest that the nature of the rate determining step depends on grain size. An optimised porosity value is also determined. In case of a limitation by the charge transfer step, the model predicts that grading both composition and reaction sites is effective in increasing the electrochemical performances whereas grading porosity is not beneficial.