In the past decades, the proton exchange membrane fuel cell (PEMFC) components, cell/stack designs and system architecture have been significantly improved. However, despite great initial performance, PEMFC systems still suffer technological limitations, such as their initial cost, partly due to the use of expensive Pt-based electrocatalyst, which prevents widespread industrial deployment. Lowering the cathode catalyst loading while keeping high (and durable) catalytic activity has been intensively studied. In this work, low-loaded catalyst layers (20 and 100 mu g(Pt) cm(geo)(-2)) are tested in PEMFC differential single-cell (DC) under high reactant stoichiometry to characterize their intrinsic electrochemical properties under various ideal and well-controlled operating conditions of cell temperature (T) and relative humidity (RH). Particularly, the change of the membrane hydration state, via the ohmic resistance measurement, and the Pt-oxides surface coverage are investigated to gather information on the physico-chemical and electrochemical mechanisms involved in the cathode active layer, and the typical performance hysteresis observed during dynamic operation such as polarization curves. These specific electrochemical measurements further enable to build a dataset, that can be used to improve PEMFC models taking into account the complex ORR mechanism, and the role of the Pt oxides in catalyst layer transient operation and degradation.

Numerous models have been developed to simulate the performance and degradation mechanisms of proton exchange membrane fuel cell (PEMFC) components. The Nernst and Butler-Volmer approaches, in a single-step reaction, often describe the hydrogen oxidation reaction (HOR) and the oxygen reduction reaction (ORR), the latter being of higher complexity as it involves numerous intermediate species. The experimental work and dataset from the first part of this study [1], obtained in differential single-cell (DC) on low-loaded cathode catalyst layers (20 and 100 mu gPt cmgeo-2 ), have been used to further study the behavior of the cathode Pt/C electrocatalyst. The objective is to introduce a detailed electrocatalytic description in one-dimensional through-thickness model, particularly the Pt surface oxide formation/reduction: the reaction is decomposed into several elementary steps associated with the surface state of Pt, as well as the formation of 'bulk' Pt-oxides, formed via the chemical place-exchange reaction under nitrogen (H2/N2) and oxygen (H2/O2) atmospheres. This electrochemical path was successfully implemented into a complete ORR performance model at the cathode; it provides a more comprehensive description of the physical and electrochemical phenomena involved in low-loaded cathode catalyst layers during non-stationary PEMFC operation, which helps to partly capture the hysteresis phenomena observed experimentally during polarization curve measurements.

To address the performance and lifetime limitations of Proton Exchange Membrane Fuel Cells, it is essential to have a comprehensive understanding of the operating heterogeneities at the cell scale, requiring the test of a wide range of operating conditions. To avoid experimental constraints, numerical simulations seem to be the most viable option. Hence, there is a need for time-efficient and accurate cell-scale models. In this intention, previous works led to the development and the experimental calibration of a pseudo-3D model of a full-size cell in a stack. To further reduce the computation time, a new spatially averaged, multi-physics, single-phase, non-isothermal, steady state pseudo-3D model is developed and calibrated with the results of the preceding model. Particularly, it captures the influence of the coolant on temperature and water mappings in the cell. Moreover, a new methodology is proposed to calibrate the electrochemical cell voltage law for new membrane-electrode assemblies. The emulation of the local operation conditions in large active surface area is realized with a small differential cell, avoiding the testing of large single cells or stacks. Subsequently, simulations are conducted to investigate the impact of the coolant temperature gradient, coolant outlet temperature and gas relative humidity.

A Proton Exchange Membrane Fuel Cell (PEMFC) is an open system. Its operation is therefore inherently heterogeneous. Indeed, in a cell, electrochemical reactions do not take place homogeneously on the active surface area. It has already been pointed out that operating heterogeneities over a large cell active area can cause a decrease of performance and durability. In fact, studies to date have focused on the relation between operating heterogeneities and local degradation on the active surface area for a small selection of operating conditions. The objective of our study is to find a way to control the current, temperature and water distributions by adjusting the operating conditions to, hopefully, optimize performance and improve durability. In order to define those control strategies, a better understanding of the heterogeneities for a wide range of operating conditions is necessary. To that end, a first numerical approach seems to be the most appropriate. This numerical study is based on a pseudo-3D multi-physics and single-phase model of a large cell, developed on COMSOL Multiphysics®. One novelty of our study, from a methodological point of view, is the calibration of the model. Instead of calibrating the model with the electrochemical response of a large cell for some chosen operating conditions as per usual, it has been calibrated with the electrochemical response of a small cell (1.8 cm²), called differential cell, emulating local operating conditions on a larger cell. Three areas of the large cell were emulated for different operating conditions: inlet, middle and outlet. Once calibrated, the pseudo-3D model was used to calculate the distributions for 108 operating conditions, which were chosen from a full factorial design of experiment defined according to the automobile application of PEMFC. The statistical analysis of these simulation results will give the influence of operating conditions (gases pressure, the magnitude and orientation of the thermal gradient of the cooling fluid, gases temperature and relative humidity) on the current density, temperature and water distributions on the active surface area. These results will later be useful for the design of strategies for controlling heterogeneities, which will be finally tested on PEM stack. Figure 1

Proper management of the liquid water and heat produced in proton exchange membrane (PEM) fuel cells remains crucial to increase both its performance and durability. In this study, a two-phase flow and multicomponent model, called two-fluid model, is developed in the commercial COMSOL Multiphysics® software to investigate the liquid water heterogeneities in large area PEM fuel cells, considering the real flow fields in the bipolar plate. A macroscopic pseudo-3D multi-layers approach has been chosen and generalized Darcy's relation is used both in the membrane-electrode assembly (MEA) and in the channel. The model considers two-phase flow and gas convection and diffusion coupled with electrochemistry and water transport through the membrane. The numerical results are compared to one-fluid model results and liquid water measurements obtained by neutron imaging for several operating conditions. Finally, according to the good agreement between the two-fluid and experimentation results, the numerical water distribution is examined in each component of the cell, exhibiting very heterogeneous water thickness over the cell surface.

Anion exchange membrane (AEM) electrolysis is the process for hydrogen generation using electricity. In this article, a 1D steady state model was introduced and elaborated to determine the performance of the AEM Electrolyser. In particular, the role of addition of Potassium Hydroxide (KOH) and its overall impact on the Multiphysics phenomenon inside the membrane electrode assembly was investigated. The simulation and experiments showed a significant reduction of the ion exchange / transport, ionic resistance as well as an improvement of the reaction kinetics at the electrodes upon addition of KOH to the pure water feedstock. The modelling efforts also resulted in a better understanding of the several Multiphysics phenomena that account for the kinetics and mass-transfer losses in the electrolyser. In particular, we also assess the fluid, geometric and flow parameters for the AEM electrolyser and the extent of their impact on the device performance.

Improving the cathode catalyst layer design requires understanding the sources of transport limitations in proton-exchange membrane fuel cells. For the purpose, a framework consisting on an electron microscopy characterization setup in couple with a numerical modeling software is proposed. The latter integrates highperforming geometry building capabilities which ensure full phase discretization (carbon, platinum, ionomer and pore phase) and freedom when designing the structure morphology and meshing. The 3D structure of the carbon phase is extracted from a focused ion beam scanning electron microscopy analysis having a 2 nm isotropic resolution. The platinum phase is built according to a nanoparticle size histogram determined from high angle annular dark field scanning transmission electron microscopy images. To add the ionomer phase, the thickness of the layer is measured on high resolution transmission electron microscopy images. The multi-physics model includes gas transport in the pores, and gas and ionic transport in the Nafion. A 4-step reaction mechanism is used to solve the electrochemistry. Numerical simulations are performed on two catalyst layer portions. The results show that structural heterogeneities can deeply impact performance. Such impact is mainly linked to oxygen diffusion limitations through the Nafion film and, to a certain extent, to interparticle competition effects.

This paper presents a study of the carbon support corrosion and mitigation strategies through the use of a pseudo-3D model. This model consists in coupling a 2D model along the channel with another model perpendicular to the flow at the rib/channel scale. Simulations offer a deeper understanding of the corrosion through the analysis of the local conditions. Rib/channel heterogeneities show the higher degradation in the zones facing the anodic rib. These results are validated qualitatively on literature data by analysis of SEM images and carbon dioxide concentration at the cathode outlet. Three mitigation strategies are studied using the model. The first one consists in speeding up the hydrogen filling of the cell. The second strategy involves an external electrical resistance to create a current leak during the startup. Third, a design study of the rib/channel is performed to minimize the cathode degradation. Whatever the mitigation strategy, it consists in reducing either the duration or the magnitude of the high cathode electrode potential.

Optimizing proton exchange membrane fuel cells (PEMFC) performance is crucial in order to attain sustainable commercialization. A major part of the issue involves understanding the role of Nafion in the catalyst layer. Nafion’s behavior on bulk mode has been extensively reported in the literature, though on ultra-thin layer mode (<20nm) its structural arrangement which dictates the transport properties highly depends on the type of substrate interfacing [1]. In PEMFC catalyst layers, Nafion covers carbon-supported platinum aggregates on ultra-thin layer mode. In these composite layers, Nafion works as a binder for the aggregates, at the same time as it is meant to ensure pathways for protons and let arrive to the catalyst surface. At high current densities, a steep performance drop is usually observed in PEMFC operation. A part of this drop is reported to be due to activation losses as a doubling of the Tafel slope is observed [2]. The origin of this Tafel slope doubling has been subject of multiple studies. Understanding the causes requires understanding the phenomena occurring at the electrode/electrolyte interface. A technique which is commonly employed is cyclic voltammetry (CV) as it can provide insights regarding these interactions. Comparative CV studies on monocrystalline platinum Pt (111) in a PFSI solution and solution exhibit distinct features, where oxide formation appears to be inhibited at the beginning of this range for PFSI [3]. These CV studies coupled with electrochemical quartz crystal microbalance (EQCM) measurements showed that when extending the potential range to 1.4V and holding the potential at 1.1V (place-exchanged oxide formation range) a large mass gain at 0.5V emerges. The origin of these features is found to be due to strongly adsorbed sulfonate groups on the platinum surface. Other works validate this behavior [4], where sulfonate groups are found to be adsorbed in both the double layer region (0.4-0.5V) and in the hydroxyl adsorption region (0.6-0.85V). In this work, the continuum model proposed by Huang et al. [5] is coupled with a reaction framework comprising multistep mechanism [6]. The adsorption of SO3- is expected to follow a Langmuirian behavior [7], indicating that the oxygen reduction reaction (ORR) is hindered through site blocking. For the adsorption of on Pt(111) a single electron transfer mechanism is assumed [8]. Kinetic parameters are obtained by fitting the model’s response to experimental data as in [6]. The simulations allow quantifying the adsorption of sulfonate groups on the platinum surface and estimating its impact on the ORR. References: 1. A. Kusoglu, A.Z. Weber, Chemical Reviews, 117 : 987-1104 (2017). 2. P. Subramanian, T.A. Greszler, J. Zhang, W. Gu, R. Makharia, Journal of The Electrochemical Society, 159(5) : B531-B540 (2012). 3. T. Masuda, F. Sonsudin, P.R. Singh, H. Naohara, K. Uosaki, The Journal of Physical Chemistry C, 117 : 15704-15709 (2013). 4. K. Kodama, R. Jinnouchi, T. Suzuki, H. Murata, T. Halanka, Y. Morimoto, Electrochemistry Communications, 36 : 26-28 (2013). 5. J. Huang, A. Malek, J. Zhang, M.H. Eikerling, The Journal of Physical Chemistry C, 120: 13587-13595 (2016). 6. B. Jayasankar, K. Karan, Electrochimica Acta, 273 : 367-378 (2018). 7. S.M. Andersen, Applied Catalysis B : Environmental, 181: 146-155 (2016). 8. K. Kodama, K. Motobayashi, A. Shinohara, N. Hasegawa, K. Kudo, R. Jinnouchi, M. Osawa, Y. Morimoto, ACS Catalysis, 8 : 694-700 (2018).

Decreasing the cost of proton exchange membrane fuel cells (PEMFC) is vital for the realization of the fuel cell vehicle market. For this challenge, it is essential not only to still reduce the electrode platinum loading but also to maintain a high performance at high current density. However, even for electrodes made with the most performant catalysts, a large performance loss is observed at high current density and this loss becomes larger as the Pt loading is lower. In operating conditions, recent work has shown that this performance loss was predominantly limited by oxygen [1] and proton transport to the catalytic surface. In order to quantify and link both effects to real active layer structural aspects a coupled modeling/imaging approach is performed. The microstructure of a real electrode is reconstructed in 3D using FIB-SEM (Fig.1a), STEM (Fig.1b) and HRTEM (Fig.1c). The first technique provides the carbon grain arrangement, whereas from the second one platinum nanoparticle size distribution is extracted. With HRTEM, an averaged-thickness is extracted for the ionomer thin layer. The raw imaging data acquired (Fig.1a) is then post-treated using a defined procedure. From the post-treated stack, certain portions that can be representative are selected according to [2]. An example is illustrated in Fig.1e with the respective raw portion in Fig.1d. From this portion, a statistically/imaging-based structure is then built in COMSOL ® Multiphysics software (Figs.1f-1h). The agglomerate 3D model is coupled with a 2D MEA model [3] – a model that allows computing local operating conditions. Studies on volume elements [2] of the catalyst layer are performed with physical input parameters as relative humidity, O2 concentration on the pore, among others, taken from the 2D MEA model. The following set of physics are included in the 3D agglomerate model: the Fickian diffusion for oxygen transport in the ionomer film – accounting for deviations of ionomer’s thin layer behaviour from bulk [4] – and in the pore phase – accounting for Knudsen effects; the ionic transport, through charge conservation equation; a kinetic model assuming a 4-step ORR reaction [5]. From the studies performed, simulation results show that the catalyst layer performance is mainly limited by oxygen diffusion in the ionomer phase and ionic transport in the primary pores [6]. Figs. 1a to 1k – Process from a raw image to numerical modeling : raw image stack (Fig.1a), platinum particle distribution from STEM acquisition (Fig.1b), HRTEM where Nafion layer can be observed (Fig.1c), portion of the image stack (Fig.1d) and the respective segmented portion (Fig.1e) ; carbon phase (brown), platinum phase (yellow), ionomer and pore phase (green and gray respectively) (Figs.1f-1h). Simulated oxygen concentration profile on Nafion (Fig.1i) and pore (Fig.1j) phases, ionic potential distribution (Fig.1k). References: 1. J.P. Owejan, J. E. Owejan, W. Gu, Journal of The Electrochemical Society, 160-(8): 824-833 (2013). 2. H.R. Sanei, R. S. Fertig III, Composites Science and Technology, 117 : 191-198 (2015). 3. B. Randrianarizafy, P. Schott, M. Chandesris, M. Gerard, Y. Bultel, International Journal Of Hydrogen Energy 43: 8907-8926 (2018). 4. Y. Kurihara, T. Mabuchi, T. Tokumasu, ECS Transactions, 75-(14): 129-137 (2016). 5. M. Moore, A. Putz, M. Secanell, Journal of the Electrochemical Society, 160-(6) : 670-681 (2013). 6. T. Mashio, K. Sato, A. Ohma, Electrochimica Acta, 140 : 238-249 (2014). Figure 1

The heterogeneous nature of the cathode catalyst layer has been a major obstacle toward the comprehension of the mechanisms hindering the PEMFC performance at high current densities. To deconvolute these, an approach coupling multiscale modeling and multiscale electron microscopy characterization-allowing to move from the local to the cathode catalyst layer scale-is adopted. Here, an agglomerate scale model is developed and coupled with a MEA-scale model. Different structures are analyzed and the effects of certain structural parameters (Pt particle size, agglomerate structure and Nafion layer thickness) on the electrode performance are quantified and discussed. Reducing the Pt particle size is found to improve performance in most cases, though the improvement margin is highly dependent on the structure, and to a certain extent, on the particle spatial distribution. It is found that thickening the Nafion film is detrimental for performance only when the porosity is not sufficiently large. Performance gains upon structure rearrangement into an ideal-type structure (Nafion and pore tortuosities minimized to unity) are also quantified. These analyses have unvealed the main mechanism limiting performance when shifting to moderate/high current densities and allowed quantifying and ranking the physical phenomena hampering performance by order of importance.

The present performance of state-of-the-art proton exchange membrane fuel cells (PEMFC) enable their commercialization, as demonstrated by the recent release of fuel-cell powered vehicles (forklifts by Plug Power, FCEV Miraï by Toyota, etc.). Now, all PEMFC manufacturers need to reduce the PEMFC systems initial cost and to enhance their durability and reliability in operation to reach the market requirements and industrial sustainability. To this goal, one must develop highly-efficient oxygen reduction reaction (ORR) electrocatalysts, which was claimed to be obtained by numerous groups in a recent past [ 1-6 ]. Unfortunately, the scientific community still struggles to obtain the best performance of these materials in operating PEFMCs: their practical performance in membrane electrode assembly (MEA) do not approach those expected from an analytical approach performed using the rotating disk electrode setup, RDE (the most widely-used setup to assess a material’s ORR performance). There are several reasons that may explain why RDE data are not relevant to account for MEA data. Firstly, in RDE, the O 2 reactant is fed as gas dissolved in the electrolyte (slow diffusivity and solubility), hence the mass-transfer rate and related limiting current density are ca. 3 orders of magnitude lower than in real PEMFC conditions. Secondly, the activity data is only extracted at high potential values in RDE ( E > 0.85 V vs RHE), although PEMFC optimal performance is reached in the 0.6 – 0.8 V vs RHE cathode potential range. Thirdly, the proton conduction can be limiting in the thin layer of ionomer covering the electrocatalyst nanoparticles in MEA, which could limit their operation, especially at the high current densities at stake in MEA. In essence, one is not sure that the electrocatalysts are used in optimized conditions in MEA, as emphasized mass-transport of reactants (both H + and O 2 ) to the catalytic sites is not granted for present ionomers and MEA structure [ 7 , 8 ]. Recent results obtained in newly-developed electrochemical characterization setups like the floating electrode (FE) [ 9 ], the gas-diffusion electrode (GDE) [ 10 ] or differential cell (DC), could enable to reach much higher ORR current densities at the lab scale and therefore better match MEA data, a prerequisite for relevant benchmarking. In the present contribution, these setups will be used to characterize three state-of-the-art ORR electrocatalysts (50 wt% Pt/Vulcan XC72, 50 wt% Pt 3 Co/Vulcan XC72 and 30 wt% Pt/graphitized carbon black), and comparison will be made with large single-cell PEMFC data in automotive conditions. We will show whether the “RDE promises” of alloyed electrocatalysts (measured in RDE configuration) do maintain in FE, GDE and DC, and whether the “advanced electrocatalysts” still exhibit their plain potential in real PEMFC catalytic layer configuration. References [1] O. Le Bacq, A. Pasturel, R. Chattot, B. Previdello, J. Nelayah, T. Asset, L. Dubau, F. Maillard, ChemCatChem, 9 (2017) 2324–2338. [2] R. Chattot, T. Asset, J. Drnec, P. Bordet, J. Nelayah, L. Dubau, F. Maillard, Nano Lett., 17 (2017) 2447-2453. [3] L. Dubau, J. Nelayah, S. Moldovan, O. Ersen, P. Bordet, J. Drnec, T. Asset, R. Chattot, F. Maillard, ACS Catal., 6 (2016) 4673-4684. [4] C. Chen, Y. Kang, Z. Huo, Z. Zhu, W. Huang, H.L. Xin, J.D. Snyder, D. Li, J.A. Herron, M. Mavrikakis, M. Chi, K.L. More, Y. Li, N.M. Markovic, G.A. Somorjai, P. Yang, V.R. Stamenkovic, Science, 343 (2014) 1339-1343. [5] L. Gan, M. Heggen, R. O'Malley, B. Theobald, P. Strasser, Nano Lett., 13 (2013) 1131-1138. [6] C. Cui, L. Gan, M. Heggen, S. Rudi, P. Strasser, Nat Mater, 12 (2013) 765-771. [7] Y. Fukuyama, T. Shiomi, T. Kotaka, Y. Tabuchi, Electrochim. Acta, 117 (2014) 367-378. [8] T.A. Greszler, D. Caulk, P. Sinha, J. Electrochem. Soc., 159 (2012) F831-F840. [9] C.M. Zalitis, D. Kramer, A.R. Kucernak, Phys. Chem. Chem. Phys., 15 (2013) 4329-4340. [10] M. Inaba, A.W. Jensen, G.W. Sievers, M. Escudero-Escribano, A. Zana, M. Arenz, Energy Environ. Sci., 11 (2018) 988-994.

The platform TRUST FC is built on the CEA/DEN thermohydraulic TRUST framework. This C++ framework is an open-source software package of Computational Fluid Dynamics (CFD) which supports massively parallel computations with a distributed memory model (MPI) [1]. The aim of TRUST FC is to improve the overall simulation of proton-exchange membrane fuel cell (PEMFC) used for the design validation step of the bipolar plates. TRUST FC contains physical models for gas, liquid, electron, ion transport and heat transfer. A model of anisotropic heat conduction is developed in TRUST FC for taking into account the in-plane and through-plane anisotropic conductivity according to the real deformation of the gas diffusion layer (GDL) by the bipolar plate in the mechanical assembly. The multi-scale modelling framework for solving PEMFC specific physics are also developed: electrochemical reactions, multi-components gas transport in porous media for GDL and catalyst layer, coupling of free flow with porous media flow [2]. The used physical models are validated on the CEA-LITEN multi-physics and multi-scale simulation platform MUSES built on Comsol Multiphysic [2] [3] and the experimental measurements [4]. TRUST FC advantages are the robust numerical methods and the massive parallelism that allows to simulate coupled multiphysics phenomena on large scale domains. TRUST FC can currently simulate a real CAD design containing tens millions of elements and numerous state variables in a few hours on our internal cluster (800 cores). SALOME is used as the meshing and visualisation tool [5]. A full simulation on a new design of bipolar plate is presented. In order to treat the coupling problem, two techniques are presented: using a conform and non-conform interface between the different domains.

The estimation and increase of the lifetime of PEM fuel cell under dynamic conditions is one of a major challenge. Increasing the durability of the fuel cell must be treated by both the development of new material and design but also by optimal strategies and management of the operating conditions of the fuel cell. The startup and shut down phase are important to optimize to reduce the carbon support corrosion [1].x Based on previous development of a multi-physics modeling framework, combining complex transport such as multicomponent transport in porous media and electrochemistry with the use of local conditions for MEA and channel design optimization [2], two 2D multi-physics models (2D model along the channel and 2D model at the rib/channel scale) are updated. The different reactions (hydrogen oxidation reaction, oxygen reduction reaction and the oxidation of the carbon support) are written in the general form [3-4]. The linking of the two models allows to simulate the transient potentials during startup and shutdown phase in two direction (along the channel and in the section of the MEA). In particular, during the injection of hydrogen in the channel, the reverse current mechanisms that accelerate the carbon support corrosion, is directly simulated without hypothesis. The validated models provide in-silico characterization to better explain the reverse current mechanisms and the interactions between the operating conditions of the cell and the local conditions in the catalyst layer. The CO2 concentration at the outlet of the channel is used as an observer to quantify the degradation of the carbon support. In a second step, different mitigation strategies are proposed. In particular, some strategies are studied to limit the high potential during the startup and shutdown phase (influence of the catalyst loading in the anode, external electrical resistance). Other strategies decrease the time during the reverse current mechanism (sensitivity of the hydrogen flow rate during the startup (Fig. sensitivity study of the hydrogen flow rate during startup on the cathodic potential and the CO2 production), design optimization of the rib/channel patern). These different strategies are explained and compared. An improvement of the carbon support corrosion is quantified and can be decreased by 50%. [1] Qiang Shen, Ming Hou, Dong Liang, Zhimin Zhou, Xiaojin Li, Zhigang Shao, and Baolian Yi. Study on the processes of start-up and shutdown in proton exchange membrane fuel cells. Journal of Power Sources, 189(2):1114–1119, 2009. [2] Bolahaga Randrianarizafy, Pascal Schott, Marion Chandesris, Mathias Gerard, and Yann Bultel. Design optimization of rib/channel patterns in a pemfc through performance heterogeneities modelling. International Journal of Hydrogen Energy, 43(18):8907 – 8926, 2018. [3] G. Maranzana, A. Lamibrac, J. Dillet, S. Abbou, S. Didierjean, and O. Lottin. Startup (and shutdown) model for polymer electrolyte membrane fuel cells. Journal of the Electrochemical Society, 162(7):F694–F706, 2015. [4] B. Randrianarizafy. Multi-physics modeling of startup and shutdown of a PEM fuel cell and study of the carbon support degradation: mitigation strategies and design optimization. PhD thesis, Communauté Université Grenoble Alpes, 2018. Figure 1

Numerical simulations for PEMFC (Proton Exchange Membrane Fuel Cell) for understanding and co-optimization of designs (bipolar plate with MEA (Membrane Electrode Assembly)) play a key role to achieve the objective of cost reduction for PEMFC. To improve the overall simulation of PEMFC used for the design validation step of the bipolar plates, very detailed physical mechanisms are included in the PEMFC models in order to describe the main electrochemical and transport mechanisms (local 2D models) [1]. Present limitation of these approaches is that they are difficult to integrate in higher scale simulations, in terms of geometry. Pseudo 3D models allow to integrate the real geometry of the bipolar plate, but with reduction in term of meshing and physics [2]. To go further, the objectives are: i/ to perform reference simulations with no compromise (in term of geometry and physics); ii/ to promote multi-physics model with open-source code, to the international community. TRUST platform is used. The platform TRUST-FC is built on the CEA/DEN thermohydraulic TRUST framework. This C++ framework is an open-source software package of Computational Fluid Dynamics (CFD) which supports massively parallel computations with a distributed memory model (MPI) [3]. TRUST-FC contains physical models for gas, liquid, electron, ion transport and heat transfer. A model of anisotropic heat conduction is developed in TRUST-FC for taking into account the in-plane and through-plane anisotropic conductivity according to the real deformation of the gas diffusion layer (GDL) by the bipolar plate in the mechanical assembly. The multi-scale modelling framework for solving PEMFC specific physics are also developed: electrochemical reactions, multi-components gas transport in porous media for GDL and catalyst layer, coupling of free flow with porous media flow [2]. The used physical models are validated on the CEA-LITEN multi-physics and multi-scale simulation platform MUSES built on Comsol Multiphysic [1-2] and the experimental measurements [4]. TRUST-FC advantages are the robust numerical methods and the massive parallelism that allows to simulate coupled multi-physics phenomena on large scale domains. TRUST-FC can currently simulate a real CAD design containing tens millions of elements and numerous state variables in a few hours on cluster. SALOME is used as the meshing and visualization tool [5]. A full simulation on a design of bipolar plate with the MEA is presented (Fig.: temperature profile on the bipolar plate, with the coupling of flow cooling and heat production of the reactions) and discussed and compared to pseudo 3D simulations on Comsol Multiphysics. [1] Randrianarizafy B., Schott P., Chandesris M., Gerard M. and Bultel Y. Design optimization of rib/channel patterns in a PEMFC through performance heterogeneities modelling. Int. J. Hydrogen Energy, 43(18):8907 8926, (2018) [2] Nandjou F.,Poirot-Crouvezier J.-P.,Chandesris M. and Bultel Y.A pseudo-3D model to investigate heat and water transport in large area fPEMg fuel cells - Part 1: Model development and validation. Int. J. Hydrogen Energy, 41(34):15545-15561, (2016) [3] https://sourceforge.net/projects/trust-platform/ [4] Robin C., Gerard M., d'Arbigny J., Schott P., Jabbour L. and Bultel Y. Development and experimental validation of a PEM fuel cell 2D-model to study heterogeneities effects along large-area cell surface. Int. J. Hydrogen Energy, 40(32):10211-10230, (2015) [5] https://www.salome-platform.org/ Figure 1

In this paper, an approach coupling an along the channel and rib-channel models has been developed to perform a design optimization of PEM fuel cell bipolar plates rib/channel patterns. Overall performance mainly results from a competition between current collection and oxygen supply. The allows proposed to investigate the effect of geometry and operating parameters on the resulting equilibrium and optimum. Moreover, heterogeneities issued from the crushing effect by the rib on the GDL are accounted. The electrochemical parameters used in the model are fitted to experimental measurements before being used in the optimization process. Results at the channel/rib scale show the competition between the oxygen supply from the gas channel to the catalyst layer and the current collection by the ribs. This understanding is possible thanks to the access to local conditions (such as the oxygen concentration) given by the model which are difficult to reach with experimental measurements. In-plane and through plane heterogeneities of current density distribution in the catalyst layer are exhibited. Design optimization is performed on the channel width/total width ratio on the cathode side. The model suggests an optimal channel design by varying its width along the flow while the standard design considers a contant ratio. This optimal channel is shown to be mainly dependent on the stoichiometry ratio of oxygen. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Proton Exchange Membrane Fuel cells (PEMFCs) durability of stacks operated under reformate is investigated with a special focus on the heterogeneity of aging. During an aging test at constant load, the local performances were investigated in situ using a segmented circuit board and a specific CO poisoning diagnostic tool based on the transition from pure hydrogen to reformate containing carbon monoxide. The heterogeneities analyses are supported with multi-physic simulations which highlight the heterogeneous CO coverage along the anode, as well as the competition between both electrodes leading to non-monotonous current density profiles. At the end of life, electrochemical and transmission electron microscopy analyses were performed on three characteristic zones (air inlet/H-2 outlet, middle and air outlet/H-2 inlet) of the Membrane Electrode Assembly (MEA). These experimental investigations put in evidence that the cathode outlet aged more severely than the cathode inlet, while more CO tolerance was lost at the anode outlet. The degradation by the electrochemical Ostwald ripening mechanism of the Pt3Co nanoparticles at the cathode outlet is suspected to pollute the ionomer, leading to the observed accelerating performance losses. Finally, optimized MEAs have been designed to mitigate the suspected degradation mechanisms, and tested at stack level demonstrating a clear durability improvement. (C) The Author(s) 2018. Published by ECS.

One of the bottlenecks hindering the usage of polymer electrolyte membrane fuel cell technology in automotive applications is the highly load-sensitive degradation of the cell components. The cell failure cases reported in the literature show localized cell component degradation, mainly caused by flow-field dependent non-uniform distribution of reactants. The existing methodologies for diagnostics of localized cell failure are either invasive or require sophisticated and expensive apparatus. In this study, with the help of a multiscale simulation framework, a single polymer electrolyte membrane fuel cell (PEMFC) model is exposed to a standardized drive cycle provided by a system model of a fuel cell car. A 2D multiphysics model of the PEMFC is used to investigate catalyst degradation due to spatio-temporal variations in the fuel cell state variables under the highly transient load cycles. A three-step (extraction, oxidation, and dissolution) model of platinum loss in the cathode catalyst layer is used to investigate the cell performance degradation due to the consequent reduction in the electro-chemical active surface area (ECSA). By using a time-upscaling methodology, we present a comparative prediction of cell end-of-life (EOL) under different driving behavior of New European Driving Cycle (NEDC) and Worldwide Harmonized Light Vehicles Test Cycle (WLTC).

Operando μ-Raman spectroscopy is used to probe the water distribution across Nafion® and Aquivion™ membranes in the operating fuel cell. The through-plane water concentration profile is obtained with μm resolution at the middle of the active surface, both at the gas distribution channel and at the under-lands areas. Depth-resolved measurements carried out at room temperature show that the water content of both membranes increases with the increase of the feed gas relative humidity and decreases with the increase of stoichiometry. At given relative humidity and stoichiometry conditions, the water content first increases at the fuel cell start-up and, then, decreases progressively with the increase of the current density delivered by the cell. The water loss is due to the concomitant rise of pressure drops and of the cell inner temperature, the latter giving the larger contribution. Pressure drops are related to the increase of the feed gases fluxes while temperature rise is due to increasing ohmic losses and heat from the electrochemical reaction. Compared to Nafion, Aquivion exhibits larger water content, but similar dehydration rate as a function of ohmic losses, and larger water accumulation at the under-lands area compared to channel.