Fuel Cell Modeling Strategic Roadmap: A Systematic Approach

Fuel cells, as devices for direct conversion of the chemical energy of a fuel into electricity by electrochemical reactions, are among the key enabling technologies for the transition to a hydrogen-based economy. Of several different types of fuel cells under development today, polymer electrolyte fuel cells (PEFCs) have been recognized as a potential future power source for zero-emission vehicles. However, to become commercially viable, PEFCs have to overcome the barrier of high catalyst cost caused by the exclusive use of platinum and platinum-based catalysts in the fuel-cell electrodes. Here we demonstrate a new class of low-cost (non-precious metal)/(heteroatomic polymer) nanocomposite catalysts for the PEFC cathode, capable of combining high oxygen-reduction activity with good performance durability. Without any optimization, the cobalt-polypyrrole composite catalyst enables power densities of about 0.15 W cm(-2) in H2-O2 fuel cells and displays no signs of performance degradation for more than 100 hours. The results of this study show that heteroatomic polymers can be used not only to stabilize the non-precious metal in the acidic environment of the PEFC cathode but also to generate active sites for oxygen reduction reaction.

Augmenting performance of fuel cells using nanofluids

Chapter 8 - FTIR and X-ray Absorption Spectroscopy of Operating Fuel Cells

Quality control (QC) is essential for the industrialization of the polymer electrolyte fuel cell (PEFC) technology, which assures the reliability of the components/sub-components, offers specification guidance for new entrants in the supply chain, and helps to reduce cost of the final product. With respect to the standardization of component/sub-component specifications, it is of great importance to identify key attributes and characterize the properties of key component and its sub-components. As the PEFC technology is being commercialized and research activities around PEFCs are being reoriented towards manufacturing issues, there is an urgent need for the QC of the key component, membrane electrode assembly (MEA), of PEFCs. As a matter of fact, the lack of standard methods, protocols and tools for the incoming, in-process and final QC of the MEA, especially, the lack of in-line, non-destructive and roll-to-roll tools for the QC of the MEA, has become one of key barriers for the PEFC commercialization.In this context, the objective of this work is to conduct a functional analysis of attributes and properties for the sub-components of the MEA, including membrane, gas diffusion layer (GDL), catalyst layer (CL), and catalyst coated membrane (CCM). To address the full spectrum of the MEA sub-components, ink is also included. The main functions of the MEA sub-components are given in Figure 1, where MPL represents the micro-porous layer of the GDL and PEM represents the proton exchange membrane or polymer electrolyte. As the attributes and properties of each MEA sub-components strongly correlate with the cell performance and longevity, this work will facilitate the investigation, diagnosis and characterization of each sub-components for the purpose of QC. This functional analysis is performed by breaking down the main functions for each sub-component of the MEA, categorizing the supporting attributes and related properties under respective functions, identifying measurement methods existing or under-development for each property and prioritizing each property for the QC of the MEA. This functional analysis links functions to attributes, properties, and measurements, with a final presentation in the format of a table with columns designated for function, attribute, property, measurement, and priority for QC.This work is accomplished through a close collaboration within a global fuel cell network, including fuel cell auto makers, fuel cell manufacturers, component suppliers, and research organizations. We believe that this work is of great importance to describe specifications and develop standards and codes for the sub-components of the key PEFC component, MEA. It is also important to identify the properties that are critical to QC. In addition, this work helps to address the discrepancy in the understanding the terms for QC along the supply chain and harmonize the language of QC. It also provides a basis for the development of QC tools for the MEA.Figure 1 Schematic of the MEA and the main functions of the MEA sub-components Figure 1

In this lecture I provide a comprehensive review on the fundamentals and practical aspects of an in-house computational modeling approach we are developing since 14 years [1-6], for the analysis of physicochemical mechanisms in electrochemical devices for energy conversion and storage such as fuel cells and rechargeable batteries [7-8]. The key feature of this approach is that it allows linking the chemical/microstructural properties of materials and components with their macroscopic efficiency and durability at the cell level, by utilizing a multi-scale framework. Since recently, the approach introduces some new capabilities (Figure): - the possibility of simulating ionic/electronic and reactants/products transport and elementary reaction steps with an immersive three-dimensional resolution (e.g. reactions leading to the formation of lithium peroxide during a Li-O2 battery discharge inside a three-dimensional pore network) through spatially-resolved Kinetic Monte Carlo (KMC) models [9-11]; - the possibility of coupling numerically "on the fly" these three-dimensional KMC simulators with continuum models (i.e. based on a set of coupled partial differential equations) describing the electrochemical operation of a complete cell, by considering relevant mass and energy conservations supported on parameters extracted from the KMC simulations and capturing the microstructural properties of the components materials [12-14]. The resulting multi-paradigm simulation framework is embedded into a single in-house software developed by us in Python/Matlab languages and called MS LIBER-T [15] which permits simulating electrochemical observables (e.g. discharge/charge curves in batteries) by tracking the three-dimensional behavior of the reactions and transport processes in the porous electrodes. Moreover, by taking into account the on-the-fly feedback between performance models and elementary kinetic models describing materials degradation, our approach is able to predict the cells performance evolution and durability as function of operation conditions (e.g. applied current density or temperature) [9,16]. The analysis and prediction capabilities of our approach is illustrated in this lecture through concrete examples in relation to the R&D on lithium air, lithium sulfur and redox flow batteries, as well as polymer electrolyte membrane fuel cells. More particularly, it is demonstrated that three-dimensional simulations provide useful guidelines for the optimized design of the porous electrodes architectures. Finally, I discuss remaining methodological and algorithmic challenges in the development of such a type of approaches to stimulate future technology breakthroughs in electrochemical energy devices.

Ohmic shorting through the membrane has been identified as one of the major failure modes in polymer electrolyte fuel cells (PEFC) [1]. Shorting occurs when electrons flow directly from the anode to the cathode instead of through the device being powered. Ohmic shorting not only can reduce the fuel cell performance, but also can lead to local heat generation in the vicinity of the short, causing membrane damage that can ultimately result in gas crossover failure. Two types of membrane shorts have been observed during the fuel cell testing: soft shorts and hard shorts. A soft short is a sub-critical short that results from the conductive carbon fibers or debris penetrating through the membrane. The soft shorts do not immediately lead to fuel cell failure; however, significant accumulation of soft shorts can reduce the overall cell resistance and compromise fuel cell durability through cell voltage degradation. A hard short is a critical short that is the result of significant heat release from an existing soft short. A hard short can directly lead to membrane crossover and cell failure. Hard shorts occur suddenly in an operating fuel cell stack where one cell develops a cell voltage reversal well below -1 V [2]. The present study is composed of two parts. The first is on the development of a test method to determine the density of soft shorts and their ohmic resistance that may lead to hard shorts when the adverse fuel cell operating conditions are met. The second part of the study is to investigate these adverse fuel cell operating conditions that lead to cell reversal and the potential hard shorts. The ultimate objective of the study is to prevent the fuel cell shorting failure through better material selection/designs and fuel cell operation controls. In the first part of this study, we use a current distribution circuit board [3] in a fixture that induces uniform compression over a 32 cm2 area of a sample that consists of a piece of proton exchange membrane or a membrane electrode assembly sandwiched between two gas diffusion layers. By incrementally increasing the compressive pressure and subjecting the sample to a voltage of 0.6 V, we can measure increasing shorting currents in some of the 0.5 cm2 current distribution segments. By de-convoluting the current density distribution measured in this experiment, the number and severity of each short can be identified and the robustness of various material sets against soft shorts can be compared. In the second part of the study, we stepwise dried out a single large-active-area fuel cell by decreasing the inlet gas dew points while under galvanostatic control. At a critical dew point, the cell potential dropped rapidly to reach a negative voltage that was limited to -1 V. Tests were conducted at various cell current densities and inlet temperatures, which showed that the corresponding cell resistance at the onset of rapid cell voltage drop decreases as the current density increases or as the temperature decreases. Good correlation is found between the cell resistance and the onset of cell reversal at various current densities. When the cell reversal limit of -1V was removed, we found that hard shorts can develop at a cell voltage around -3V, confirming the importance of operating the fuel cell within the operating window developed in this study. A.B. LaConti, M. Hamdan, R.C. McDonald, Mechanism of Membrane Degradation for PEMFCs, in Mechanisms of Membrane Degradation for PEMFCs, in: W. Vielstich, A. Lamn, H.A. Gasteiger (Eds), Handbook of Fuel Cells: Fundamentals, Technology and Applications, Vol. 3, John Wiley & Sons, New York, 2003, pp. 647–662.Gittleman, C. S., Coms, F. D., and Lai, Y. H., "Chapter 2: Membrane Durability: Physical and Chemical Degradation", Polymer Electrolyte Fuel Cell Degradation, Editors: Matthew M. Mench, E. Caglan Kumbur, T. Nejat Veziroglu, Elsevier (2012).J.J. Gagliardo, J.P. Owejan, T.A.Trabold, and T.W.Tighe, Nucl. Instrum. Meth. A, 605 (2009) 115-118.

Platinum and platinum-alloy oxygen reduction reaction (ORR) catalysts have been implemented in the prototype, and by now also in commercial fuel cell power systems for automotive applications, successfully meeting the demanding conditions of relatively low temperature (80°C) and high acidity operating conditions of the polymer electrolyte fuel cell (PEFC). However, due to the high price of Pt, the catalyst cost is projected to account for as much as a half of the total PEFC stack cost.1 In this context, the potential replacement of Pt-based catalysts, especially in the fuel cell cathode, with non-precious metal catalysts (NPMCs) is expected to significantly reduce PEFC stack cost. Achieving such a cost benefit is, however, contingent upon reaching sufficient activity and durability with NPMC for the ORR, a requirement that the electrocatalysis research community has been striving to meet. In this presentation, we expand upon the idea of combining nitrogen precursors during NPMC synthesis to improve the performance and performance durability of non-precious metal ORR catalysts. Previously, we introduced a new non-precious metal ORR catalyst derived from two nitrogen precursors with different decomposition temperatures: easily decomposing cyanamide (CM) and more thermally stable polyaniline (PANI).2 In this approach, CM acts as an efficient pore-forming agent that allows for the formation of a highly porous structure, which in particular benefits the high-current response of the resulting electrocatalyst. Compared to the alternative approach utilizing metal-organic frameworks (MOFs),3,4 the use of cyanamide promises a very significant reduction in the NPMC cost, without sacrificing ORR activity. In an effort to further improve the PEFC performance of the two nitrogen-precursor NPMCs, we have explored approaches involving the use of ammonia treatment, the addition of various carbon supports, and inclusion of multiple transition metals. In this presentation, we will summarize the results of these studies, which have involved the extensive use of characterization techniques, such as X-ray photoelectron spectroscopy, scanning electron microscopy, scanning transmission electron microscopy, X-ray diffraction, surface area/pore distribution measurements, and nano-scale X-ray computed tomography. In the conclusion, we will also define critical factors for enhancing the performance of NPMCs in the PEFC cathode and outline directions for future research. Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. Microscopy research supported through a user project at ORNL’s Center for Nanomaterials Sciences, which is an Office of Science User Facility. References Spendelow et al., DOE Fuel Cell Technologies Office, Fuel Cell System Cost-2013, (2013).Hoon T. Chung et al., “Combined nitrogen precursor approach to develop highly active non-precious metal oxygen reduction reaction catalyst.” in preparation.S. Ma et al., “Cobalt Imidazolate Framework as Precursor for Oxygen Reduction Reaction Electrocatalysts,” Chem. Eur. J. 17, 2063 (2011).Proietti et al., “Iron-based cathode catalyst with enhanced power density in polymer electrolyte membrane fuel cells,” Nat. Commun. 2, 416 (2011)

Metallic Bipolar Plates for Polymer Electrolyte Fuel Cell (PEFC) used in electric vehicles. Electric vehicles use electrolytic polymeric fuel cells (PEFCs) built of bipolar sheet metal. Along with the MEA, One of the most essential components of a PEFC cell is the bipolar plate. since they support the MEA, provide rigidi-ty to the layer, and even allow for gas diffusion. Electrical conductivity is provided by the entire electrode surface. The control of heat and the ejection of product water are two additional benefits of a well-prepared bipolar plate [103-105]. In the PEFC stack, bipolar plates are placed between the MEAs so that each of them offers a link to one end of a MEA and, on the other side, to the cath of an adjacent MEA. Bi-polar panels should be small and thin to reduce For PEMFCs, a variety of metal bipolar plates are now being investigated to suit the demands of lowering costs, increasing stacking size, lowering weight, and raising energy density. The quality of interest strategy was compared to the best answer (TOPSIS) the multi-attribute decision-making approach (MADM) in this work, the optimal substance for a metallic bi-polar plate is selected using (MADM). For electrolyte polymer fuel cells (PEFCs), which can have numer-ous competing objectives? Material designers can choose the best material based on preset criteria with the use of a suggested algorithm tool. The theoretical framework is followed by a case study on the mate-rial selection for a PEFC bipolar plate. A list of all the products that meet the requirements for selection, including production costs, by dividing each of our objectives by a user-supplied weight, we divide our audience into a single goal via the weighted sum approach. One of the most popular methods is this one. When considering overall weights, one concern is determining how much weight to give each goal. The primary goal governs are added with varying weights in the weighed total approach, and the sum is then optimized. The goal that function is optimized while another is constrained to a variable's value in the electrically operated constraint approach you can generate an integrated analysis by combining several inputs and weights using the Total Weight function. In that several raster inputs representing various fac-tors can be easily mixed, mixing weights or relative importance, it is comparable to the Weighted Overlay function. 316 austenitic stainless steel,310 austenitic stainless steel,317l austenitic stainless steel,316l aus-tenitic stainless steel, aluminum (gold plated), aisi 446 ferritic stainless steel, aisi 436 ferritic stainless steel, aisi 444 ferritic stainless stee, aisi 434 ferritic stainless stee,304 austenitic stainless steel, titanium (coated with nitride), a560 (50cr–ni). the density of an object, the tensile strength, the expansions coeffi-cients, conductivity of heat, thermal diffusivity, and fracture toughness are some of the other characteris-tics of bipolar plates that should be considered. From the result it is seen that titanium (coated with ni-tride) is got the first rank whereas is the 310 austenitic stainless steel having the lowest rank. The first ranking titanium (coated with nitride) is obtained with the lowest quality of 310 austenitic stainless steel.

As energy demand increases and global warming progresses, expectations for fuel cells, which generate electricity through chemical reactions between hydrogen and oxygen, are rising. There are various types of fuel cells, which are classified according to the electrolyte. Polymer electrolyte fuel cells (PEFCs) are expected to be used in stationary power sources for home use and fuel cell vehicles because of their low operating temperature, short start-up time, and ease of miniaturization. The cost has been an issue in the widespread use of fuel cells. The amount of platinum used in the catalyst layer (CL) must be reduced to reduce costs. However, it increases the current density per unit area of platinum. There are three factors that contribute to voltage drop: ohmic polarization, activation polarization, and diffusion polarization. At high current densities, the voltage drop due to diffusion polarization is dominant. The main cause of diffusion polarization is the transport resistance of oxygen molecules in the CL, and improving the oxygen transport properties in the CL will lead to lower cost PEFCs. In this study, we analyzed the transport properties of oxygen molecules in the CLs of PEFCs using the Monte Carlo (MC) method. The effect of oxygen scattering on the overall oxygen transport properties was investigated by considering the behavior on the surface of the ionomer film (surface diffusion) into the MC method, which simulates the overall transport in the PEFC CL. The objective of this study is to reproduce accurate oxygen transport by comparing the results of MC and molecular dynamics (MD) methods. First, we used the MC method to analyze oxygen scattering phenomena. In this study, we used the 3D structure data of CL in the MC simulations. The three-dimensional structure of the sample was reconstructed from sequential slice images. Molecules were assumed to reflect specularly on the boundaries of the simulation domain. Oxygen molecules were randomly placed in the simulation system. The time step was set at 5 ps and the simulation time was set at 4 μs. In order to examine the effect of surface diffusion on the transport properties of oxygen molecules, the simulation was performed using various conditions of surface diffusion. We calculated the effective diffusion coefficient of oxygen in the CL as the transport property of oxygen molecules in the MC method. As the surface diffusion coefficient increases, the effective diffusion coefficient of oxygen increases. When the surface diffusion coefficient is small, the effective diffusion coefficient of oxygen increases due to a decrease in the time constant, which determines the probability distribution of the surface residence time. However, when the surface diffusion coefficient is large, a different trend emerges. As the time constant increases, the effective diffusion coefficient has a peak value and then decreases. Next, to verify the model of surface diffusion in the MC method, we analyzed the scattering phenomenon of oxygen molecules in a simulation system that simulates the pores in the CL using the MD method. We modeled the nano pores in the CL as a slit between the ionomer walls in the MD method. Nafion with the equivalent weight (EW) of 1146 was used as polymer model. The number of Nafion chains is set at 4, and the water content λ is set at 7. Three-dimensional periodic boundary conditions were applied to the simulation domain. After the system was equilibrated, 1 ns of NVT simulation was performed for production. The temperature was set at 297 K. The behavior of oxygen molecules impacting on the ionomer wall was analyzed. We analyzed the behavior of oxygen molecules colliding with the ionomer membrane using the MD method. The average residence time of surface diffusion on the ionomer thin film was of the order of 10-10s. When the calculation results were compared with the MC results, it was found that the average residence time obtained by the MD method was the value where the surface diffusion coefficient affects much on the effective diffusion coefficient. Comparing the results of the MD method with the surface diffusion model used in the MC method, there are some discrepancies between the results and the model. For example, the MC method used a model in which oxygen molecules reflect diffusively on the ionomer surface. However, in the MD method, it was found that oxygen molecules tend to reflect in the direction of travel (Fig. 1). Therefore, a more accurate model of the MC method needs to be developed in the future. Figure 1

Rod Borup is a Team Leader in the fuel cell program at Los Alamos National Lab in Los Alamos, New Mexico. He received his B.S.E. in Chemical Engineering from the University of Iowa in 1988 and his Ph.D. from the University of Washington in 1993. He has worked on fuel cell technology since 1994, working in the areas of hydrogen production and PEM fuel cell stack components. He has been awarded 12 U.S. patents, authored over 40 papers related to fuel cell technology, and presented over 50 oral papers at national meetings. His current main research area is related to water transport in PEM fuel cells and PEM fuel cell durability. Recently, he was awarded the 2005 DOE Hydrogen Program R&D Award for the most significant R&D contribution of the year for his team's work in fuel cell durability and was the Principal Investigator for the 2004 Fuel Cell Seminar (San Antonio, TX, USA) Best Poster Award. Jeremy Meyers is an Assistant Professor of materials science and engineering and mechanical engineering at the University of Texas at Austin, where his research focuses on the development of electrochemical energy systems and materials. Prior to joining the faculty at Texas, Jeremy workedmore » as manager of the advanced transportation technology group at UTC Power, where he was responsible for developing new system designs and components for automotive PEM fuel cell power plants. While at UTC Power, Jeremy led several customer development projects and a DOE-sponsored investigation into novel catalysts and membranes for PEM fuel cells. Jeremy has coauthored several papers on key mechanisms of fuel cell degradation and is a co-inventor of several patents. In 2006, Jeremy and several colleagues received the George Mead Medal, UTC's highest award for engineering achievement, and he served as the co-chair of the Gordon Research Conference on fuel cells. Jeremy received his Ph.D. in Chemical Engineering from the University of California at Berkeley and holds a Bachelor's Degree in Chemical Engineering from Stanford University. Bryan Pivovar received his B.S. in Chemical Engineering from the University of Wisconsin in 1994. He completed his Ph.D. in Chemical Engineering at the University of Minnesota in 2000 under the direction of Profs. Ed Cussler and Bill Smyrl, studying transport properties in fuel cell electrolytes. He continued working in the area of polymer electrolyte fuel cells at Los Alamos National Laboratory as a post-doc (2000-2001), as a technical staff member (2001-2005), and in his current position as a team leader (2005-present). In this time, Bryan's research has expanded to include further aspects of fuel cell operation, including electrodes, subfreezing effects, alternative polymers, hydroxide conductors, fuel cell interfaces, impurities, water transport, and high-temperature membranes. Bryan has served at various levels in national and international conferences and workshops, including organizing a DOE sponsored workshop on freezing effects in fuel cells and an ARO sponsored workshop on alkaline membrane fuel cells, and he was co-chair of the 2007 Gordon Research Conference on Fuel Cells. Minoru Inaba is a Professor at the Department of Molecular Science and Technology, Faculty of Engineering, Doshisha University, Japan. He received his B.Sc. from the Faculty of Engineering, Kyoto University, in 1984 and his M.Sc. in 1986 and his Dr. Eng. in 1995 from the Graduate School of Engineering, Kyoto University. He has worked on electrochemical energy conversion systems including fuel cells and lithium-ion batteries at Kyoto University (1992-2002) and at Doshisha University (2002-present). His primary research interest is the durability of polymer electrolyte fuel cells (PEFCs), in particular, membrane degradation, and he has been involved in NEDO R&D research projects on PEFC durability since 2001. He has authored over 140 technical papers and 30 review articles. Kenichiro Ota is a Professor of the Chemical Energy Laboratory at the Graduate School of Engineering, Yokohama National University, Japan. He received his B.S.E. in Applied Chemistry from the University of Tokyo in 1968 and his Ph.D. from the University of Tokyo in 1973. He has worked on hydrogen energy and fuel cells since 1974, working on materials science for fuel cells and water electrolysis. He has published more than 150 original papers, 70 review papers, and 50 scientific books. He is now the president of the Hydrogen Energy Systems Society of Japan, the chairman of the Fuel Cell Research Group of the Electrochemical Society of Japan, and the chairman of the National Committee for the Standardization of the Stationary Fuel Cells. ABSTRACT TRUNCATED« less

This paper presents a study of direct conversion of chemical energy into electrical energy during the combustion of a (80Zr + 20CuO)–(LiF + CaF2 + MgF2)–(15Zr + 85CuO) thin three-layer condensed energy system, which is a high-temperature galvanic cell. It is determined that this cell during combustion generates an electric signal with an amplitude of 1.6 V and a half-width of 15 s. Its formation mechanism is proposed. A time-resolving X-ray diffraction method is used to identify the phases formed.

Fuel Cells. Fuel cells are electrochemical devices that convert the chemical energy of a fuel directly into electrical and thermal energy. In a typical fuel cell, gaseous fuels are fed continuously to the anode (negative electrode) compartment, and an oxidant, eg, oxygen or air, is fed continuously to the cathode (positive electrode) compartment. The electrochemical reactions take place at the electrodes to produce an electric (direct) current. The fuel cell theoretically has the capability of producing electrical energy for as long as the fuel and oxidant are fed to the electrodes. In reality, degradation or malfunction of components limits the practical operating life of fuel cells. Besides the direct production of electricity, heat is also produced in fuel cells. This heat can be effectively utilized for the generation of additional electricity or for other purposes, depending on the temperature. A practical consideration for fuel cells is compatibility with the available fuels and oxidants. One of the main attractive features of fuel cell systems is the expected high fuel‐to‐electricity efficiency. This efficiency, which runs from 40–60% based on the lower heating value (LHV) of the fuel, is higher than that of almost all other energy conversion systems. The two primary impediments to the widespread use of fuel cells are high initial cost and short operational lifetime. A variety of fuel cells has been developed for terrestrial and space applications. Fuel cells are usually classified according to the type of electrolyte used in the cells as polymer electrolyte fuel cell (PEFC), alkaline fuel cell (AFC), phosphoric acid fuel cell (PAFC), molten carbonate fuel cell (MCFC), and solid oxide fuel cell (SOFC). Fuel cells operating on pure H 2 and O 2 provide a useful power source in remote areas such as in space or under the sea where system weight and volume are important parameters. On the other hand, fuel cell power plants operating on fossil fuels and air offer the potential for environmentally acceptable, highly efficient, and low cost power generation. The minimum technical requirements for fuel cells for four different types of applications, ie, for buildings, industry, transportation, and utilities are given. From the standpoint of commercialization of fuel cell technologies, there are two challenges: initial cost and reliable life. Several activities, would strongly boost the prospects for fuel cell technology and include the development of (1) an active electrocatalyst for the direct electrochemical oxidation of methanol; (2) improved electrocatalysts for oxygen reduction; and (3) a more CO‐tolerant electrocatalyst for hydrogen.

Overview Polymer Electrolyte Fuel Cell (PEFC) is expected as a new power source in automobiles with high power density and low emission. Although PEFC has many advantages compared with internal combustion engines, the cost reduction and the improvement of performance and durability are needed for its practical application. For improvement of PEFC, it is important to understand the mechanism inside it under various operating and structural conditions and to feedback into the design of membrane electrode assembly (MEA) and bipolar plate constituting fuel cell stack.In order to visualize inside PEFC, we have been developed a numerical simulation tool calculating the cell and stack performance and physical distributions and a nondestructive, real-time/space visualization technique for oxygen partial pressure in the cathode flow channel and the GDL using oxygen-sensitive luminescent dye film [1].In this study, as for the first step of our numerical modeling development, the effects of operating condition, for example, cathode flow rate on the test cell as well as commercial-sized cell and stack were investigated. Numerical Modeling Inside the fuel cell, multi-physical and multi-scale of phenomena such as multi-component gas, liquid water and heat transport inside the flow channel and the GDL, electrochemical reactions and proton/water transport in the MEA are nonlinearly coupled [2]. These phenomena require too much calculation cost to be solved in high resolution by fully 3-dimensional equations based on computed fluid dynamics (CFD), so it is necessary to apply simplified models. In our modeling, macroscopic models are applied for microscopic phenomena in the catalyst layer and electrolyte such as electrochemical reactions (HOR/ORR) and proton/water transport. And these models are coupled with multi-dimensional heat, gas and liquid water transport equations in which effective parameters such as gas diffusivity and permeability in the GDL and equivalent hydraulic diameter in the flow field of bipolar plate and the manifold of stack are included [3]. Results First of all, the performance of 25cm2test cell with single serpentine flow channel was carried out. Hydrogen and air flow rate is 300ml/min, relative humidity is 60%RH, cell temperature is 353.15K and back pressure is 1atm, respectively.The distribution of oxygen partial pressure in cathode flow channel and on the GDL surface at cathode utilization 80% (0.58 A/cm2) are shown in Figure 1 compared to the measured data by a nondestructive visualization system. The results are good agreement with the measured data and indicate that the numerical prediction of current density distribution is valid in our model.Applying the validated model, the effect of cathode flow rate on the performance of short stack with 20 cells (max. 5kW) was carried out. As for the other operating conditions, relative humidity is 50%RH, cell temperature is 343.15K and back pressure is 1.5atm, respectively. Figure 2 shows the effect of cathode utilization on the distribution of normalized in-flow rate and ORR gain for each cell at 0.5A/cm2. As cathode utilization increases, in-flow rate decreases and ORR gain increases remarkably near the dead end of stack. This is because liquid water accumulates in the flow channel and the GDL.In addition, the performance of full-scale PEFC stack for automobiles under various operating conditions will also be discussed in this meeting.

Ionomer membrane degradation in polymer electrolyte fuel cell (PEFC) becomes one of the most urgent and critical problems that decrease the longevity of a PEFC, thereby limiting its development with good efficiency and affordability 1. Adding ceria into the PEFC system has proven to be a promising and sustainable way to mitigate this chemical membrane degradation, as the cerium ions can quench the radicals before they attack the ionomer membrane 2. Understanding the distribution and movement of cerium ions within a fuel cell membrane is essential for improving the design of a PEFC system, in terms of its operating environment, material properties, boundary conditions, etc., whereas this has rarely been studied. Due to the experimental limitations of measuring cerium ions transport in an operating fuel cell, numerical simulation becomes a practical approach to quantitatively analyse cerium ions migration under certain conditions.In this study, we aim to provide: (1) a reliable and practical simulation approach to investigate 2D distribution of the cerium ions under specific conditions; and (2) a flexible strategy to analyse the migration of cerium ions attributed to a variety of factors. These techniques would support future research into the development of a promising fuel cell not only with longevity but also at a sustainable cost.From the simulation, we quantified many factors that have impacts on the migration of cerium ions. The diffusion coefficient of cerium ion with respect to the local water content, as well as how the ions are drugged by the local water diffusion, was obtained at first by performing molecular dynamics simulations. Then, by combining these results into a computational fluid dynamics simulation using finite volume method, transport of the cerium ions under certain conditions was resolved (see Figure 1).Along the direction of the path from anode to cathode side, the ion transport in the membrane is affected more substantially by the electric field rather than the water convection and its self-diffusion. Meanwhile in the membrane cross-section plane, it is mainly affected by the water diffusion and its self-diffusion. As the primary finding, the electric field has the greatest influence on the transport of cerium ions, while local distribution of the water content plays an important role when the electric potential difference is small. Credibility of these preliminary simulation results was confirmed by comparing against experimental observations at the similar fuel cell operating environments.Detailed settings of the material properties and results on the reactions of cerium ions to various fuel cell environments will be discussed in the presentation. Acknowledgement This study is support by New Energy and Industrial Technology Development Organisation (NEDO) and the integrated supercomputer system at Institute Fluid Science, Tohoku University. Reference [1] Wang, Y.; Chen, K. S.; Mishler, J.; Cho, S. C.; Adroher, X. C. A Review of Polymer Electrolyte Membrane Fuel Cells: Technology, Applications, and Needs on Fundamental Research. Appl. Energy 2011, 88 (4), 981–1007.[2] Wong, K. H.; Kjeang, E. In-Situ Modeling of Chemical Membrane Degradation and Mitigation in Ceria-Supported Fuel Cells. J. Electrochem. Soc. 2017, 164 (12), F1179–F1186. Figure 1

Polymer electrolyte fuel cells (PEFCs) are suitable for fuel cell vehicles (FCVs) because the PEFCs have high efficiency, high responsibility and high performance, but the critical issues of PEFCs are the cost and the durability of the fuel cell stack. The development of PEFCs requires increased operating temperature, over 100 °C, for high efficiency FCV systems. In addition, the PEFCs of fuel cell buses and trucks need to have higher durability of the fuel cell stack than that of passenger cars. With increasing operating temperature under start-up/shut-down condition, carbon black supports for platinum undergo accelerated corrosion, while niobium-doped tin oxide supports undergo negligible corrosion. We invented a highly durable SnO2 nanoparticle support with a “fused aggregate network structure” as a new candidate to replace carbon [1-4] and found a novel platinum anti-dissolution mechanism of Pt/Nb-SnO2 cathode catalyst layers (CLs) during load cycling under an oxygen atmosphere, which was not found in the case of Pt/GCB (graphitized carbon black) CLs. The load cycle durability of Pt/Nb-SnO2 CLs increased with increasing cathode oxygen concentration, while that of Pt/GCB CLs decreased. When the Pt nanoparticles (NPs) on the Nb-SnO2 support are oxidized by oxygen in the cathode at the open circuit voltage (OCV), the availability of free electrons in the Pt NPs decrease, and thus the supply of free electrons to the depletion layer on the surface of Nb-SnO2 becomes difficult. This effect would be particularly evident for the high cathode oxygen concentration [5]. The Pt loading amount for both the Pt/Nb-SnO2 cathode catalyst and the Pt/CB anode catalyst was 0.1 mg cm-2. The cell performances were evaluated under H2/O2 at 80 °C and 100% RH before and after the durability evaluations. Fig. 1 shows the protocols for the durability evaluation as a function of OCV holding time (2 s, 60 s) using galvanostatic operation under H2/air conditions, and upper cell potential holding time (2 s, 60 s) using potentiostatic operation under H2/N2 conditions. The protocols of Figs. 1(c) and (d) simulate the durability evaluations of Figs. 1(a) and (b). Fig. 2 shows the normalized cell performances at 1.0 A cm-2 after the durability evaluations under H2/O2 conditions at 80 °C and 100% RH. The cell performances were nearly the same before and after the durability evaluations with OCV (upper cell potential) holding time of 2 s during H2/N2 and H2/air operation. In the case of the durability evaluations with OCV (upper cell potential) holding time of 60 s, the cell performance deterioration after the durability evaluations during H2/air operation was suppressed as compared with that under H2/N2 operation. Fig. 3 shows the decrease rate of ohmic resistance during the durability evaluations at lower cell voltage as a function of OCV (upper cell potential) holding time. The decrease rate was the highest of all during the durability evaluations with OCV holding time of 60 s during H2/air operation. We reported that the degradation of Pt NPs on the Nb-SnO2 support is suppressed by means of the formation of a depletion layer existing on the surface of the Nb-SnO2 support with increasing cathode oxygen concentration at the OCV [5]. The OCV holding time in the presence of the oxygen would influence the growth of the depletion layer on the surface of the Nb-SnO2 support during load cycling. We will discuss in detail the effects of OCV/load holding time, relative humidity, and operating temperature on the load cycle durability of Pt/Nb-SnO2 cathode catalyst layers. Acknowledgement This work was partially supported by funds for the “Superlative, Stable, and Scalable Performance Fuel Cell (SPer-FC)” Project from the New Energy and Industrial Technology Development Organization (NEDO) of Japan. References K. Kakinuma, M. Uchida, T. Kamino, H. Uchida, and M. Watanabe, Electrochim. Acta, 56, 2881 (2011).K. Kakinuma, Y. Chino, Y. Senoo, M. Uchida, T. Kamino, H. Uchida, S. Deki, and M. Watanabe, Electrochim. Acta, 110, 316 (2013).Y. Chino, K. Kakinuma, D. A. Tryk, M. Watanabe, and M. Uchida, J. Electrochem. Soc., 163(2), F97 (2016).K. Kakinuma, R. Kobayashi, A. Iiyama, and M. Uchida, J. Electrochem. Soc., 165(15) J3083 (2018).C. Takei, R. Kobayashi, Y. Mizushita, Y. Hiramitsu, K. Kakinuma, and M. Uchida, J. Electrochem. Soc., 165(16), F1300 (2018). Figure 1