(Invited) Diagnostics of Fuel-Cell Performance Utilizing Simple Graphical Methods Based on Theoretical Limiting Cases

Several emerging and growing applications like biosensors, gas separation membranes, protective coatings, photonics, nanocomposites and microelectronics depend on polymers of thicknesses under 100nm[1]. Ion conducting polymers (ionomers) of thickness <100nm have induced significant advances in the performance of polymer-electrolyte fuel cells (PEFCs) by serving as binder in the catalyst layers (CLs), aiding proton conduction and extending the reaction zone of the CL porous electrode.[2] Thin and ultra-thin polymer films provide ease of processing, application specific tunable properties and reduction in material cost. However, due to deviation of nano-confined polymers from bulk behavior, they pose a challenge of predictability. This is evident in PEFCs where thin-film ionomers are large contributors to mass-transport losses at low catalyst loadings required for commercialization. In-situ investigations over the past 10 years have provided a significant amount of insight into these losses in CLs.[3] As a result, it would be misleading to employ the same principles of understanding used for bulk polymers for nano-confined polymers without modification. In our study, we aim to understand nano-confined ionomers in two ways. First, looking at impact of interfaces by using ionomers supported on different substrates and tuning substrate-ionomer interaction via reducing and oxidizing environment. Second, by examining the impact of cooperative motion and chain dynamics using thermal expansion study of nano-confined ionomers. Combining these two studies we can gain new understanding of effect of confinement on performance. Understanding ionomer-catalyst surface interface and interaction can elucidate not only how ionomers impact catalyst performance but also how catalyst surface impacts ionomer performance. In our study we use water uptake and modulus to probe the effect of platinum surface on thin-film ionomers under oxidizing(Air) and reducing(H2) conditions. Several in-situ and ex-situ methods have demonstrated that oxide formation on the active platinum catalyst surface can reduce the catalytic activity, further hampering activity in the cathode catalyst layer[4]. Despite this, our studies show continued growth of oxides on platinum surface results in higher density of water maintained in the ionomer. This indicates that nano-confined ionomers have greater water stability in the cathode than on the anode catalyst layer, enhancing proton transport in the cathode catalyst layer. Using transition temperature as a proxy for material behavior, we also looked at relaxation behavior of nano-confined ionomers under slow heating conditions. For glass-forming polymers like perfluorinated sulfonic-acid (PFSA) ionomers (such as Nafion and 3M-ionomer) cooperative motion and dynamics of chains have been used to explain changes in modulus, thermal expansion, relaxation behavior, and gas transport. Thermal transition temperatures are often used as a broad physical description for these kinetically and thermodynamically-driven changes in polymer behavior[1]. In this study, we used heated cell ellipsometry to explore the presence of transition temperatures and their dependence on thickness and substrate in thin-film ionomers. We are able to see both α and β transition temperatures using ion exchanged nano-confined ionomers supported on silicon substrates. Our results demonstrate increased rate of expansion for thin films as compared to bulk and dramatic change of transition temperatures around 50-70nm indicating impact of ionomer-surface interaction and influence of electrostatic interaction on chain relaxation and gas transport. Acknowledgement We would like to thank Douglas Kushner for providing assistance and guidance in this study. This work made use of facilities at the Joint Center for Artificial Photosynthesis at Lawrence Berkeley National Laboratory. This work was funded in part by the University of California Chancellor's Graduate Fellowship, National Science Foundation Graduate Fellowship and the Fuel Cell Technologies Office, Office of Energy Efficiency and Renewable Energy, U. S. Department of Energy under contract number DE-AC02-05CH11231.

Polymer electrolyte fuel cells (PEFCs) offer the prospects to revolutionize the transportation by powering not only automotive but also and heavy-duty vehicles. In PEFCs, ionomers are used to function as a proton-exchange membrane (PEM) facilitating ion transport between the catalyst layers (CLs). In addition, ionomer also function as an electrolyte binder mixed with the catalyst supports and particles to facilitate mass transport of reactants to catalytic sites. When confined to nanometer thicknesses in a heterogeneous CL structure, ionomer properties exhibit a range of properties form bulk (membrane) to thin films, and influenced by ionic and interfacial interactions.Diverse functionalities, operating environment and performance metrics in fuel cells require optimized ionomer multi-functionalities for both PEM and CLs. While reducing the thickness of PEM is commonly considered an effective strategy for improving device performance by minimizing transport losses, this was considered purely from the perspective of geometric effects and cost constraints. However, how thickness affects intrinsic properties of an ionomer from membrane to electrode structures remains to be an open question. On one hand, efforts towards improving performance and durability of PEFCs require chemically and mechanically supported PEMs, which introduce additional interactions with the secondary support materials. An improvement in transport functionality in these ionomer, however, compromises stability and separator functionality, thereby setting a constraint to their optimization. On the other hand, improving CL ionomers require an understanding of their structure in the presence of confinement and electro-catalyst interactions. Between these duality, a new paradigm for fuel-cell ionomers, where one needs to understand and tune ionomer interactions with secondary particles across a wide spectrum of thicknesses, from bulk to nm.This talk will present an overview of ionomers from this perspective with a focus on structure-property relationship of perfluorosulfonic acid (PFSA) ionomer, in both CL and PEM regime, which enables identification of the structural transitions relevant to fuel-cell functionality. Building upon a systematic investigation of membranes in micrometer thickness range (100 to a few µm), combined with nanometer-thick supported films in sub-micron range, a comprehensive material property map is generated for PFSAs, from mechanical properties, to water and ion transport. Our data links thickness-dependent changes in bulk membrane functionality to confinement-induced changes in catalyst-ionomer structure. Given the distinct functionality expected of ionomers in these regimes, our results are used to first expand the design space of ionomer using previously overlooked thickness as a design lever, and then to identify key transition regimes to elucidate the governing phenomena and demonstrate the combinatory roles of thickness and interactions in ionomer performance. The results will be evaluated to provide a new paradigm for ionomers in hybrid structures, from composites membrane to electrodes, and to expand the ionomer parameter space enabling optimization strategies for performance and durability in fuel cells. Acknowledgment AK acknowledges the ECS-Toyota Fellowship and the funding from the Fuel-Cell Performance and Durability (FC-PAD) consortium through the Fuel Cell Technologies Office, Energy Efficiency, and Renewable Energy Office of the U.S. Department of Energy (DOE), (contract no. DE-AC02-05CH11231)

Platinum alloys catalyze oxygen reduction in conventional polymer-electrolyte fuel cells [1]. The platinum is deposited on carbon, and the nature of the carbon support affects cell polarization. Two commonly used carbon blacks are Vulcan and Ketjenblack. Vulcan (V) has a relatively low surface area of (228 m2/g [2]) and ~95% of the Pt resides on the external surface [3]. Ketjenblack (KB) has a higher surface area, 891 m2/g [2], and ~60% of the Pt resides in micropores in the carbon [3]. Pt/KB displays higher catalytic activity, while Pt/V exhibits better performance at high current densities. Pt inside micropores is not in direct contact with ionomer and, consequently, is not poisoned by adsorbed anions. However, Pt inside KB micropores is relatively inaccessible to oxygen and protons, which detrimentally affects performance at high current densities [4].The area-specific impedance of catalyst layers is frequently measured by operating cells with nitrogen at the working electrode, to create a blocking electrode, and hydrogen at the counter electrode [5, 6, 7, 8]. The area-specific impedance of the catalyst layer can be determined from the difference between the maximum value of the real part of the impedance at low frequency and the intercept of the impedance with the real axis at high frequency. The area-specific resistance of a catalyst layer determined in this way is R = l⸱(3κ)-1, where l is the thickness of the catalyst layer and k is the effective conductivity of ionomer.Recently, Harzer et al. deposited platinum on Ketjenblack by different techniques [4]. They fabricated two electrodes with platinum preferentially on the external surface of carbon black, and one electrode with platinum preferentially inside micropores like commercial Pt/KB. They measured higher resistance to oxygen transport, higher values of R, and larger polarization on oxygen at high current densities on catalyst layers having platinum predominantly in micropores. They postulated that higher R was caused by a poorer distribution of ionomer. A different hypothesis is considered in this work: that ohmic losses in micropores contribute significantly to R. Firstly, a formula is developed to describe the impedance of a blocking electrode with substantial resistance inside micropores. Secondly, the model is used to interpret the experiments of Harzer et al. and estimate the conductivity of the pore solution that would fit their results. Acknowledgements: This work was funded under the Fuel Cell Performance and Durability Consortium (FC-PAD), by the Fuel Cell Technologies Office (FCTO), Office of Energy Efficiency and Renewable Energy (EERE), of the U.S. Department of Energy under contract number DE-EE0007652. This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States Government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof.

In this work, an analytical model of the microporous layer (MPL) and the catalyst layer (CL) interface under compression is developed to investigate the effects of the MPL|CL interfacial morphology on the ohmic and mass transport losses at the MPL|CL interface in a polymer electrolyte fuel cell (PEFC). The model utilizes experimentally measured surface profile data as input. Results indicate that the uncompressed surface morphology of mating materials, the elasticity of PEFC components, and the local compression pressure are the key parameters that influence the characteristics of the MPL and CL contact. The model predicts that a 50% drop in the MPL and CL surface roughness may result in nearly a 40% drop in the MPL|CL contact resistance. The model also shows that the void space along the MPL|CL interface can potentially store a significant amount of liquid water , which could result in performance loss and reduced durability. A 50% drop in the MPL and CL surface roughness is expected to yield nearly a 50% drop in the water storage capacity of the MPL|CL interface. The results of this work provide key insights that will enhance our understanding regarding the complex relation between MPL|CL interfacial structure and cell performance.

Polymer electrolyte fuel cells (PEFCs), a promising source of clean energy in automotive application, still require durability improvement before commercialization. For instance, cationic impurities may get introduced into the PEFCs from the ambient air (e.g. roadside contaminants) and from the corrosion of stack and balance of plant components which are known to have a severe negative effect on the durability and performance of PEFCs such as reduction in proton conductivity and water content in the membrane (1). In our group, the experimental and theoretical study of the effects of key cathode side cation contaminants on the performance of PEFCs were investigated, and the understanding of contamination mechanism was utilized to develop novel technologies for mitigating the effects of contamination. A list of cation contaminants (Na+, K+, Mg+2, Ca+2, Ni+2, Ba+2, Al+3, Cr+3, and Fe+3) were tested for screening studies and one cation was selected for more in-depth studies that was not previously well investigated, prevalent in roadside impurities, and abundant in the nature. The contaminant was tested with a single cell, a segmented cell, and a multilayer membrane cell test configurations. In the cation computational model, for the first time, a catalyst agglomerate model was utilized and a decrease in oxygen concentration in the catalyst layer was found due to cation contamination which was a new finding (2). During experimental studies, it was found that water management significantly affects contamination by cations which may result in salt precipitation causing serious mass transport losses, and salt was preferentially deposited at the outlet of the cell at our operating conditions. It was also found that GDL played an important role in the transport of cations in as well as out of the MEA, and hydrophobic nature of the GDL can act as a barrier to the transport of cation solution. Based on experimental and computational model, mitigation methodologies for cation contamination were designed depending on the presence of contaminants in various parts of the fuel cell. Cation contaminants from the membrane can be completely removed by re-protonating the membrane using acidic solution. For removing salt deposit, an ex-situ acid flush technique was utilized and salt deposit on flow field was completely removed, whereas some white patches of salt deposit still was observed on the GDL (Figure 1). Ex-situ mitigation process using acidic solution worked well, but additional factors need to be identified that hinder the full recovery process. Acknowledg e ments Financial support from the Department of Energy (DOE)-EERE, DE-EE00000467 (University of Hawaii, prime contractor, Jean St-Pierre, PI) is greatly acknowledged. References T. Okada, in Handbook of Fuel Cells– Fundamentals, Technology and Applications, W. Vielstich, H. A. Gasteiger, A. Lamm and H. Yokokawa, Editors, John Wiley & Sons, Ltd, New York (2010).M. A. Uddin and U. Pasaogullari, J. Electrochem. Soc., 61, F1081 (2014). Figure 1

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)

Hydrogen-fueled polymer electrolyte fuel cell (PEFCs) systems are currently utilized as high efficiency, low emission power sources for a variety of applications, most notably for electric vehicles such as the Toyota Mirai. The high cost of platinum, widely used as the electrocatalyst in PEFCs, is one of main barriers to the widespread and economically-viable implementation of fuel cell vehicles. Many research efforts have successfully developed platinum group metal-free (PGM-free) electrocatalysts for the oxygen reduction reaction (ORR), including those in the U.S. Department of Energy, Fuel Cell Technologies Office’s Electrocatalysis Consortium (ElectroCat)1-3. High-throughput catalyst synthesis, activity evaluation, and performance testing are core activities within ElectroCat aimed at accelerating the discovery and implementation of ORR electrocatalysts. High-throughput catalyst activity screening is accomplished using a newly-developed multi-channel flow double electrode, allowing activity measurements of four catalysts simultaneously deposited on glassy carbon electrodes using an automated robotic catalyst ink dispensing system with a nano-liter injector4. The purpose of this project is to accelerate the development of PGM-free catalysts using high-throughput performance evaluation in a 25-electrode array cell (NuVant) which has a common counter electrode and five independent flow channels. This system allows simultaneous performance testing and characterization of 25 types of catalyst in a membrane-electrode assembly (MEA) with five gas supply manifolds. Electrode fabrication is one of the most challenging steps in the catalyst-coated membrane (CCM) fabrication process for the array cell. A custom-designed heated vacuum table mounted on the computer-controlled XY table is used to make the 25-electrode CCM to avoid shrinkage and swelling of the catalyst layer and the membrane during the fabrication. The nano-pipette automated ink deposition system is being used for precise and even catalyst ink deposition across the small circular array electrodes. Scanning electron microscopy of the electrode is being utilized to confirm uniform and robust microstructures after the direct fabrication method. The 25-electrode set-up can accelerate PGM-free catalyst evaluation and optimization of electrode composition with the additional advantage of minimizing the amount of material required since the area of each electrode in the array is less than 1 cm2. Acknowledgements This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the auspices of the Electrocatalysis Consortium (ElectroCat). Argonne National Laboratory is managed for the U.S Department of Energy by the University of Chicago Argonne, LLC, under contract DE-AC-02-06CH11357. References U. Martinez, S. K. Babu, E. F. Holby, K. Artyushkova, L. Lin, H. T. Chung, G. M. Purdy, and P. Zelenay, 232nd ECS Meeting, National Harbor, MD, October 1-5, 2017.S.T. Thompson, A.R. Wilson, P. Zelenay, D.J. Myers, K.L. More, K.C. Neyerlin, and D. Papageorgopoulos, Solid State Ionics, 319 (2018) 68-76.H.T. Chung, D.A. Cullen, D. Higgins, B.T. Sneed, E.F. Holby, K.L. More, P. Zelenay, Science 357 (2017) 479–484.J. Park, N. Kariuki, D. J. Myers, H. Chung, U. Martinez, P. Zelenay, 233nd ECS Meeting, Seattle, WA, May 13-17, 2018.

Rising levels of greenhouse gas emissions, especially carbon dioxide (CO2), are regarded as one of the causes of global warming in recent years. To develop technologies for reducing CO2emission plays an important role for vehicle manufacturers, and Nissan has been developing zero-emission vehicles (ZEVs) such as battery electric vehicles (BEVs) and fuel cell electric vehicles (FCEVs). The biggest issues to penetrate FCEVs into the market are cost reduction of polymer electrolyte fuel cell (PEFC) power system including hydrogen storage subsystem, and development of hydrogen infrastructure. Related to the former issue, one of the most significant challenges is to reduce platinum group metals (PGM) in fuel cell stacks. PGM are used as electrocatalyst and contained in catalyst layers (CLs) of membrane electrode assemblies (MEAs) in the stack. Various kinds of research activities on PEFC electrocatalyst have been reported so far, indicating high oxygen reduction reaction (ORR) activity and durability mainly measured in aqueous electrolyte systems such as a rotating disk electrode method.1-8 On the other hand, electrocatalyst is mixed with electrolyte to form CLs through deposition and solidification process. From industrial point of view, it is needed that performance of the electrocatalyst should be guaranteed as CL in MEA. CL is a multi-scale component, i.e. micro-scale porous electrode consisting of nano-scale materials (Fig. 1), where electrochemical reaction and mass transport occur simultaneously. Micro and nano structure of CL has been revealed gradually by means of characterization techniques remarkably progressed recently, such as electron microscope. 9-10However, it is still under development to characterize and diagnose structure and properties of CLs as overall and average value. To reduce PGM usage, so far Nissan has been doing research and development on CL based on the strategy to understand the correlation between CL/MEA performance and the consisting materials through properties and structure via key mechanism.11-20In this presentation, diagnostics of PEFC CLs related to activity and mass transport are explained, mainly focusing on the unique analysis Nissan has been developing thus far.

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

The composition and processing of the catalyst-ionomer ink used to fabricate electrochemical energy conversion device electrodes can impact the final electrode microstructure and performance. Parameters influencing the microstructure and performance are, for example, solvent ratio, ink processing method and time, ionomer chemistry, and carbon morphology/porosity. Polymer electrolyte fuel cell (PEFC) cathodes are typically prepared by first dispersing a catalyst powder, comprised of platinum or platinum alloy nanoparticles supported on carbon blacks, with ionomer in solvents, followed by extensive mixing using a variety of methods. The electrode properties are controlled by the interactions of the ionomer with the catalyst particles and the support in the catalyst-ionomer ink, by the effect of ink solvent composition on those interactions, and by the ink mixing and coating procedures. This presentation will describe the in-situ/ex-situ ultra-small angle X-ray scattering (USAXS) combined with SAXS studies of the evolution of the cathode catalyst layer to determine the effect of ink processing variables and ink composition on the ink properties, especially on the carbon agglomerate break-up for efficient coating of catalyst layers while optimizing fuel cell performance and durability. The effect of ink formulation is examined for Pt-supported Vulcan carbon (Pt/Vu) and Pt and PtCo-supported on high surface area carbon (Pt and PtCo/HSC) with different ionomers. The results provide the fundamental understanding enabling improved membrane-electrode assembly (MEA) performance and durability. Moreover, the results of the evolution of the catalyst layer during the ink drying process as a function of solvent removal rate and solvent identity will be discussed. Acknowledgments This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office under the M2FCT Consortium. This work was authored in Argonne National Laboratory, a U.S. Department of Energy (DOE) Office of Science laboratory operated for DOE by UChicago Argonne, LLC under contract no. DE-AC02-06CH11357. This research used the resources of the Advanced Photon Source (APS), a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory under Contract No. DE-AC02-06CH11357.

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

Polymer electrolyte fuel cells (PEFCs) are expected as a next-generation power sources due to their low emissions and high efficiencies. However, it is required to improve the power density at lower Pt loading. It is known that the losses of the power density are caused by activation losses, ohmic losses and mass transport losses, and that the mass transport losses are dominant at higher current density. Moreover, it is suggested that one of the causes of the mass transport losses is the shortage of oxygen in the cathode side of PEFC. In the cathodic catalyst layer, there are Pt catalysts on supported carbon microparticles, and those particles are covered with ionomer films which are composed of polymer electrolytes and water molecules. The ionomer has two properties for the water-generating reactions in the cathodic catalyst layer: the proton conductivity and the oxygen permeability. In particular, the dependence of the oxygen permeability on water content has not been clear. In this study, we analyzed water content dependence of oxygen permeation properties in ionomer on Pt surface using molecular dynamics simulations. Regarding the calculation system, Nafion was adopted to the polymer electrolyte in the ionomer, and water content, λ, was defined as the ratio of the number of sulfo groups in Nafion to the number of water molecules. We set λ = 3, 7, 11 and constructed a system of an equilibrium state of ionomer on Pt surface at each water content. Then oxygen molecules were inserted above the ionomer and permeate the ionomer along the thickness direction at steady state. Firstly, the density distributions were obtained to evaluate the structural properties of the ionomer. As a result, the region of the ionomer is divided into three region: ionomer/gas interface, bulk region, ionomer/Pt interface. Next, the number of permeated oxygen molecules through the ionomer was counted, and the oxygen permeability of the ionomer was estimated at different water content. As a result, the oxygen permeability decreases with increasing water content. Gas permeability is estimated using the permeation coefficient which is obtained by the product of the diffusion coefficient and solubility coefficient of gas molecules, indicating that the diffusivity and solubility are governing factors of the permeability. Therefore, the oxygen diffusivity and solubility was evaluated to discuss the oxygen permeation mechanism in the ionomer. The oxygen diffusion coefficient was obtained by the density distribution of the oxygen molecules along the thickness direction using the Fick’s law. As a result, the oxygen diffusivity in each region of the ionomer decreases at lower water content while slightly increases at higher water content, with the increase in water content. On the other hand, the oxygen solubility coefficient was calculated using the test-particle-insertion method, and the solubility in each region of the ionomer decreases with increasing water content. Finally, the oxygen permeability was evaluated using the diffusivity and solubility in each region. Consequently, the oxygen permeability decreases with increasing water content in each region, and the permeability in the ionomer/Pt interface is the smallest, which indicates that the oxygen dissolution in the ionomer/Pt interface is dominant in the oxygen permeation through the ionomer.

Polymer electrolyte fuel cell (PEFCs) is a potential power source for new-generation automobiles like fuel cell vehicles that run on hydrogen energy, it has been studied a lot for last decades in order to use as the power sources of automotive. The most important characteristics of PEFCs are low operation temperature and quick start and shutdown. However, the properties of PEFCs are still limited due to its high cost and insufficient durability and performance.Since oxygen reduction reaction (ORR) at the cathode is the dominant reaction in PEFCs, oxygen proton and electron have to be transferred smoothly in porous catalyst layer. Under normal operating conditions, oxygen transfer is the dominant factor of limiting current density, therefore, oxygen transfer must be increased from the gas channel to the Pt surface through various porous media and various components.On the other hand, inkjet printing has been considered to be an economical and easy scale-up technology for the micro-scale patterning and fabrication as one of the on-demand methods in a variety of field because it allows for the patterning of various ink. In addition, it can reduce the process time, cost and the toxic waste created during the manufacturing process. Also, this method can be easily applied to perform ink composition studies. Especially for fuel cell applications, inkjet printing resolves many of the problems associated with previous methods of catalyst deposition by allowing a uniform distribution of catalyst ink onto the surface of GDL or membrane and by loading a very low amount of catalyst.So in this research, in order to increase the performance of polymer electrolyte cells, the oxygen diffusion resistance was tested based on the difference of surface of catalyst layer in cathode by using inkjet method. Firstly, we mixed carbon supported Pt catalyst, distilled water and 20wt% Nafion solution and NPA together and then use homogenizer to disperse the liquid, then we got the catalyst ink. The Second step was fabrication of cathode catalyst layer (CCL) by using inkjet method. Third step was to observe the morphology for CCL with catalyst ink, in order to know the length and the height of a drop of ink, we made a sample, and then we took this sample to observe through laser microscope. When we got the basic information about morphology of CCL, we fabricated catalyst layer by inkjet, and took it to do the MEA evaluation and characterization to investigate their electrochemical properties, such as I-V curves, limiting current densities and impedance. And in order to compare with the experimental results, a theoretical model of the 3D structure was also circulated and discussed. From this model and measured data, it was confirmed that the better electrochemical properties results from 3D structure of catalyst layer in cathode.

The activity of oxygen reduction reaction (ORR) catalysts often determine performance of polymer electrolyte fuel cells (PEFCs) as measured by their power output, open circuit voltage, and fuel conversion efficiency. Currently, Pt-nanoparticle catalysts, either supported on high surface-area carbons or prepared in a form of contiguous thin layer on conductive or non-conductive supports, represent the state of the art in ORR electrocatalysis at the PEFC cathode. However, the high and variable price and scarceness of Pt have limited its widespread implementation in the -temperature fuel cells to date, especially in automotive transportation. Under these circumstances, platinum group metal-free (PGM-free) ORR catalysts have received growing attention in recent years as a possible replacement for Pt-based formulations. The progress achieved since the development of the first nature-inspired electrocatalysts of oxygen reduction in the seminal work by Jasinski in the 1960s (Nature 201, 1212, 1964), which mostly happened through the broad implementation of the high-temperature synthesis approach, makes replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this this presentation, we will summarize recent progress in research targeting development of high-performance PGM-free catalysts for oxygen reduction reaction (ORR) at Los Alamos National Laboratory. Two approaches will be discussed in a greater detail: (i) the approach involving fine-tuning of the catalyst porosity and surface area using pore-forming compounds and (ii) the method specifically focusing on the development of atomically dispersed transition metal moieties and avoiding the formation of transition metal-rich nanoparticles during the heat treatment of catalyst precursors. We will demonstrate the impact that porosity/surface area optimization, through the use of either pore formers (cyanamide, ZnCl2) precursor templating (metal organic frameworks) or both, can have on the fuel cell performance of PGM-free catalysts. We will also show how modifications to the electrode structure through the change in the ionomer content and ionomer equivalent weight can lead to substantial improvements in the fuel cell performance at both low- and high current densities (aerial power density of more than 0.50 W/cm2 in H2-air testing at 80°C). Finally, we will recapitulate the challenges still facing PGM-free research that, in spite of all the progress achieved in recent years, is yet to produce materials capable of competing with the incumbent Pt-based catalysts in terms of oxygen reduction activity, performance durability, and cost (specifically, when extended to the overall cost of a fuel cell stack). Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged.

We have been researching manufacturing methods of catalyst layers in order to improve the effective utilization rate of Pt in polymer electrolyte fuel cells. In our previous research1-3, we demonstrated experimentally that an electrospray (ES) method was able to make great progress in the interface formation between the electrolyte polymer ionomer and the Pt supported on carbon1,3 or conductive ceramics2, and that the immediate drying of the catalyst layer ink also greatly contributes to the improvement of Pt effectiveness. Since the ink droplets had already dried when these were deposited on the membrane, we proposed that the ink drying process can be reduced and that the cost of producing the catalyst layer is also greatly reduced. However, since the amount of catalyst applied is very small with a single nozzle, we also proposed that a multi-nozzle system is indispensable in order to adapt to the actual catalyst layer formation process.Therefore, we are jointly developing the ES manufacturing system with a multi-nozzle device (Fig. 1a) in a collaboration between the University of Yamanashi and Meiko Co., Ltd. We developed the first prototype machine, MES-Lab.α, for R & D, which features options such as nozzle material, multi-nozzle structure, coating treatment of nozzle tip, nozzle fixing adhesive, suck-back method, and ink energization method, among others. We have completed a new design for a basic 72-nozzle block (Fig. 1b), which incorporates all of the above new materials and new structures and is compatible with the production of industry-standard electrodes (5 cm x 5 cm).The performance of the PEFC cell using the cathode catalyst layer produced by this ES device was superior to that of a cell using the conventional pulse-swirl-spray device (PSS). We prepared the catalyst layer according to two different ionization methods (positive (ESP), and negative (ESN) ionization), and compared these with that prepared by the PSS method.3 The catalyst layers prepared by ESN successfully mitigated oxygen transport resistance. The highest porosity, which induced better water management, revealed superior performance at high current. Moreover, we confirmed the importance of the proton conduction in the catalyst layer through the ionomer contents. Thinly coated ionomer film on the catalyst surface revealed that lower resistance originates from the ionomer film on the Pt surface, RCL, film , but poor σ H+cath. , as evaluated for low contents of ionomer in the catalyst layer. These results also suggest that we will be able to achieve superior actual cell performance for catalyst layers prepared via ES using modified ionomer chemical structures, for which there is enhanced H+ conductivity, σ H+cath. , via, e.g., increased ion exchange capacity, and oxygen permeability3 (Fig. 2). Acknowledgement This work was partially supported by funds for the “Superlative, stable, and scalable performance fuel cell” (SPer-FC) and the “Electrolytes, catalysts and catalyst layers with extraordinary efficiency, power and durability for PEFCs to 2030” (ECCEED’30-FC) projects from the New Energy and Industrial Technology Development Organization (NEDO) and the “Yamanashi Frontier for Innovation and Ecosystem” (FCyFINE) project from the Regional Innovation Ecosystems Program of the Ministry of Education, Culture, Sports, Science and Technology (MEXT). References Takahashi, K. Kakinuma, and M. Uchida, J. Electrochem. Soc., 163, F1182-F1188 (2016).Takahashi, R. Koda, K. Kakinuma, and M. Uchida, J. Electrochem. Soc., 164, F235-F242 (2017).Cho, K. Tamoto, and M. Uchida, Energy Fuels, 34, 14853−14863 (2020). Figure 1