High-Throughput Activity and Performance Screening Methods for PGM-Free Catalysts

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.

The development of durable and highly active platinum group metal-free (PGM-free) electrocatalysts is key to overcoming the greatest barrier in the commercialization of fuel cell electric vehicles: the high cost and limited availability of PGM catalysts utilized in polymer electrolyte fuel cells. While the majority of research on PGM-free catalysts has focused on developing active and selective materials for the sluggish oxygen reduction reaction (ORR), minimal work has been devoted to the understanding of the physical and chemical structure of active PGM-free catalysts and its relationship with the long-term stability of these novel materials. This understanding is imperative for the further development of next-generation PGM-free catalysts with improved activity and durability that could ultimately replace PGM-based ORR catalysts in fuel cells. PGM-free catalysts with high volumetric activity, four-electron selectivity (i.e., low hydrogen peroxide yield), and long-term stability in highly acidic and strongly oxidizing environment of the fuel cell cathode are desired as replacements for PGM-based ORR catalysts. For this presentation, state-of-the-art PGM-free ORR catalysts, developed by our group [1, 2], which are obtained via high-temperature treatment of dual nitrogen precursors, cyanamide (CM) and polyaniline (PANI), different transition metal precursors (Fe, Co, Mn), and with or without carbon support are used as model PGM-free catalyst systems. Depending on the transition metal used, catalysts with different physical and electrochemical characteristic properties are obtained. Specifically, Fe-based catalysts are generally known for their high activity and low peroxide yield generation. However, Co- and Mn-based catalysts generate highly graphitic structures which could improve catalyst long-term stability. In this work, structure-activity-durability relationships are developed based on comprehensive physical, chemical, and electrochemical characterization of highly active (CM+PANI)-Me-C catalysts (Me = Fe, Co, Mn), correlating properties such as carbon structure, elemental speciation, and CO2 generation. Acknowledgement Financial support for this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. [1] Chung, H.T., Holby, E.F., Purdy, G.M., Babu, S.K., Litster, S., Cullen, D.A. More, K.L., Zelenay, P. (2015). “Combining Nitrogen Precursors in Synthesis of Non-Precious Metal ORR Catalysts with Improved Fuel Cell Performance.” ECS Meeting s, MA2015-02 (37), 1278. [2] Martinez, U., Holby, E.F., Dumont, J.H., Chung, H.T., Zelenay, P. (2016) “Non-PGM ORR Catalysts Based on Transition Metals Alternative to Iron.” ECS Meeting s, MA2016-01, 1719.

Platinum group metal-free (PGM-free) catalysts for oxygen reduction reaction (ORR) in polymer electrolyte fuel cells have emerged as a promising alternative to PGM-based catalysts thanks to their abundance in the Earth crust and, consequently, low cost. Metal-nitrogen-carbon (M-N-C) catalysts possibly represent the most attractive PGM-free ORR materials. However, despite the significant progress accomplished in M-N-C catalyst development over the past two decades, this class of materials continues to face challenges that need to be overcome to narrow the performance gap to PGM-based catalysts.[1] Our team has made significant efforts to improve the activity and stability of M-N-C catalysts by developing novel synthesis approaches, such as the ‘dual-zone’ synthesis, targeting specifically improvements in catalyst stability.[2, 3] We have also established standardized protocols for the activity and stability evaluation of PGM-free catalysts under relevant operating conditions of the fuel cell.[4] Additionally, our modeling of PGM-free M-N-C ORR electrocatalysts has provided much needed insight into the materials and helped with their optimization. We have utilized machine learning methods coupled with high-throughput synthesis and characterization to optimize the conditions for a variety of synthesis approaches, which has led to substantial increase in experimentally realized activity.[5, 6] Our prior fundamental studies of ORR activity [1, 2, 7, 8] and materials stability [9] at the density functional theory (DFT) level are actively being linked to achieve simultaneously high activity and long-term stability through a Pareto optimization. Coupling machine learning and DFT efforts is presently underway.In this talk, we will summarize our recent progress in the development of PGM-free M-N-C catalysts for ORR, focusing on improvements in catalyst activity and stability from both experimental and theoretical perspectives. We will highlight various synthesis strategies for improving catalyst activity and stability, and key design principles for M-N-C catalysts, learned from DFT calculations and machine learning-driven, high-throughput catalyst synthesis. We will also discuss the challenges and opportunities in the development of PGM-free catalysts for ORR. Overall, PGM-free catalysts represent a promising pathway for the advancement of low-cost and efficient fuel cell technologies. References Martinez, U. et al., J. Electrochem. Soc., 2019. 166, F3136.Chung, H.T. et al., Science, 2017. 357, 479.Zelenay, P. and D. Myers, ElectroCat (Electrocatalysis Consortium); U.S. Department of Energy Hydrogen and Fuel Cell Program Annual Merit Review 2019. https://www.hydrogen.energy.gov/pdfs/review19/fc160_myers_zelenay_2019_o.pdf.Zhang, H. et al., Nat. Catal., 2022. 5 (5): 455.Kort-Kamp, W.J.M. et al. . J. Power Sources, 2023. 559: 232583.Karim, M.R. et al., ACS Appl. Energy Mater.. 2020. 3 (9): 9083.Holby, E.F., Curr. Opin. Electrochem., 2021. 25, 100631.Anderson, A.B. and E. F. Holby, J. Phys. Chem. C, 2019. 123 (30): 18398.Holby, E.F., G. Wang, and P. Zelenay, ACS Catal., 2020. 10 (24): 14527.

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.

Commercial low-temperature polymer electrolyte membrane fuel cells (PEMFCs) rely on expensive platinum-based catalysts to drive the oxygen reduction reaction at the cathode. In order to overcome cost barriers limiting market penetration in both transportation and stationary applications, significant efforts are being made to develop suitable platinum group metal-free (PGM-free) catalysts. The latest classes of PGM-free catalysts show very promising mass activity, but the poor durability of these carbon-based materials is still a significant challenge that must to be addressed. In this effort, advanced analytical electron microscopy methods were employed to study the degradation pathways of PGM-free catalysts which were submitted to accelerated stress tests. Catalysts provided by four different suppliers were tested concurrently in a specially designed segmented fuel cell. Polarization curves were recorded both before and after a durability stress test which involved 10k square wave cycles between 0.95 – 0.60 V in air. Analytical electron microscopy performed across a wide length scale (sub-nanometer to micron) will be presented which links the observed performance losses with changes to the atomically dispersed active sites, carbon support, and ionomer distribution. The advantages and disadvantages of different catalyst precursors (metal organic frameworks, cyanamide/polyaniline, etc.) will also be discussed from a durability standpoint. This work was supported by the U.S. Department of Energy, Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office under the Electrocatalysis Consortium (ElectroCat). Microscopy was performed as part of a user project at ORNL’s Center for Nanophase Materials Sciences (CNMS), which is a DOE Office of Science User Facility

Platinum group metal-free (PGM-free) oxygen reduction reaction (ORR) electrocatalysts have demonstrated substantial improvements in electrochemical cell and fuel cell performance in the last decade. However, the durability of these catalysts is still insufficient for the implementation of these catalysts in polymer electrolyte fuel cells (PEFCs), particularly in automotive power systems. Recently, carbon oxidation has been reported as a main cause for the destruction of ORR active sites in heat-treated metal-nitrogen-carbon (M-N-C) PGM-free catalysts (1). This result suggests that in order to improve their durability, M-N-C catalysts should be synthesized at as high a temperature as possible to maximize the graphitic content thereby making the catalyst more oxidation resistant. An optimum heat-treatment temperature for the best ORR activity of M-N-C catalysts depends on many factors, including the synthesis approach, type of precursors used, and the precursor ratio. One more factor to account for, based on the reasoning above, is the need to maximize the heat-treatment temperature without sacrificing catalyst activity. In this work we have found that for the high-temperature synthesis of active M-N-C catalysts, the most important factors are the selection of the nitrogen precursor, adjustment of the precursor ratio, and the choice of the synthesis route. Without fine-tuning of the synthesis conditions, the ORR activity of the PGM-free catalysts usually decreases when heat-treated above 900° C. By selecting an appropriate synthesis route and catalyst precursors we have been able to perform synthesis at 1100° C and obtain catalysts that show high RDE activity (E½ of 0.81 V vs. RHE, Figure 1). In this presentation, we will summarize the electrochemical and fuel cell performance of these catalysts, with particular emphasis on their durability. Acknowledgement Financial support of this research by DOE-EERE through Fuel Cell Technologies Office is gratefully acknowledged. Microscopy research was supported through a user project at ORNL’s Center for Nanophase Materials Sciences, which is an Office of Science User Facility. Reference Choi Chang Hyuck, Claudio Baldizzone, Jan-Philipp Grote, Anna K. Schuppert, Frédéric Jaouen, and Karl J. J. Mayrhofer, Stability of Fe-N-C Catalysts in Acidic Medium Studied by Operando Spectroscopy. Angew. Chem. Int. Ed. 54, 1 (2015). Figure 1

Nano-structured platinum group metal-free catalysts and their integration in fuel cell electrode architectures

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

The development of platinum group metal-free (PGM)-free catalysts with comparable performance and durability to low- PGM catalysts would hasten the cost competitiveness of fuel cells with alternative technologies. Therefore, addressing electrocatalyst development represents the most pressing technical barrier in fuel cell deployment and in meeting the ultimate U.S. Department of Energy (DOE) automotive fuel cell system cost target of $30/kW. ElectroCat (The Electrocatalysis Consortium), like other DOE Energy Materials Network (EMN) consortia, aligns research and development (R&D) activities at national laboratories and, through DOE-funded projects, facilitates access of academic and industry partners to the world-class capabilities and expertise at the national labs. These capabilities, such as (1) catalyst synthesis (including in particular high-throughput methods), (2) advanced characterization expertise, and (3) quantum chemical modeling address the salient knowledge gaps in PGM-free catalyst development: ascertaining the structure-function relationship, increasing active site density, improving electrode structure to maximize active site utilization and mitigate mass transport limitations, and improving durability. In the near-term, the consortium will work to develop PGM-free catalysts and electrodes to meet the 2025 DOE current density technical target of 0.044 A/cm2 at 0.9 VIR-free, analogous to the goal for low-PGM catalysts. In 2018, ElectroCat R&D efforts increased initial activity by 68% compared to the 2016 baseline of 16 mA/cm2. The presentation will highlight current R&D advancements, core national lab experimental and computational capabilities, as well as high-throughput and machine-learning approaches to expedite the development of PGM-free catalysts and electrodes.

Platinum group metal (PGM)-free catalysts for oxygen reduction reaction (ORR) have attracted significant attention in the last two decades. These catalysts typically perform better in alkaline aqueous electrolytes than in their acidic counterparts.1, 2 However, the performance of PGM-free ORR catalysts in anion exchange membrane fuels cells (AEMFCs) have been consistently lower than in the acidic polymer electrolyte fuel cells (PEFCs). The most likely reasons for the sub-par behavior of PGM-free catalysts in AEMFCs has been often linked to difficulties in preparing electrodes with anion exchange ionomers and assuring efficient water management. These challenges have been amplified by the high-loading requirement for PGM-free ORR catalysts, resulting in electrodes by as much as an order of magnitude thicker than the PGM-based ones.In this presentation, we will demonstrate AEMFCs with much improved performance of the PGM-free cathode (Fe-N-C catalyst-based). The performance improvement has been achieved by optimizing the electrode fabrication process, including changes to the electrode configuration and catalyst ink preparation. These changes have allowed us to elevate the AEMFC performance, including the peak power density of > 0.8 W cm-2 in H2-O2 cells, to the level comparable to that of the corresponding PEFC, operating with a PGM-free cathode under the same operating conditions.

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)

Direct methanol fuel cells (DMFC) have several advantages for a broad spectrum of energy density demanding applications, ranging from portable devices to stationary backup power. DMFCs deliver power at high efficiencies compared to internal combustion technologies and uses high energy density methanol as the fuel. However, DMFCs face several challenges, including methanol crossover at the cathode and slow methanol oxidation reaction (MOR) kinetics at the anode that impede its DMFC performance relative to hydrogen polymer electrolyte fuel cells (PEFCs). Since the the anode is a much bigger source of overpotentials than the H2 PEFC, we must carefully consider it’s characteristics in designing the membrane electrode assembly (MEA) and it requires extensive experimental and modeling studies to investigate these hindrances and mitigate their impacts on performance. It is widely known that vapor-fed DMFCs suffer less from methanol crossover. However, a complete understanding of the vapor-fed MOR kinetics in porous electrodes is lacking. When modeling DMFCs it is a common practice to assume that the reaction order of the MOR is zero. However previous studies have shown that the liquid-fed MOR on PtRu/C catalysts has areaction order of 0.5 [1, 2]. However, we found that the reaction order of the vapor-fed MOR can differ from that value. We also investigated the effect of different catalyst loading and the effect of methanol crossover on reaction order.This material is based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Fuel Cell Technologies Office (FCTO) under Award Number DE-EE0008440. References S.Lj. Gojkovic´ et al., Electrochimica Acta 48 (2003) 3607/3614D. Chu, S. Gilman, J. Electrochem. Soc. 143 (1996) 1685.

Anion exchange membrane fuel cells (AEMFCs) offer considerable advantages over proton exchange membrane fuel cells (PEMFCs) in that the kinetics for oxygen reduction reaction (ORR) are greatly improved in alkaline media [1]. The improved kinetics of ORR in alkaline media thus allows for the use of PGM-Free catalysts in AEMFCs. Though there have been many efforts to develop PGM-Free cathode catalysts for AEMFCs, PGM-Free anode catalysts, with catalytic activity for HOR comparable to Pt, are still in the early stages of development [2]. The slow development of these AEMFC anode catalysts is largely due to the lack of compatible ionomers for anion exchange. However, recent development of anion exchange ionomers show great improvements over PEMFC ionomers, such as NAFION, in AEMFCs [3]. Carbon supported nickel has been shown to have high activity for HOR in AEMFCs, however the susceptibility of Ni to electrochemical oxidation, as well as the less than optimal hydrogen binding energy to the Ni active site, suggest there is further room for optimization of the Ni/C system [1]. Here, we have proposed to address these issues through alloying Ni with transition metals to tune the electronic environment of Ni, as well as to improve the corrosion resistance of Ni in alkaline media. For this project, catalysts are prepared by an incipient wetness method using the metal nitrates as catalyst precursors and KetjenblackÒ, DENKA BLACKÒ, graphene oxide (GO) and reduced graphene oxide (rGO) as support materials. GO and rGO have been prepared from Hummers’ method. In some cases, a sacrificial support method is also used to control the primary particle size of the NiM materials. Figure 1 shows the open circuit and close circuit polarization curves for NiMo/C with peak power density observed for HOR of ~ 120 mW/cm2, which is an encouraging result though not competitive with Pt or Pd. Therefore, our aim is to explore the role of the alloying metal (M = Mo, W, Cr, Co, Cu) as well as to investigate the role of the carbon support (ex: GO, rGO, N-doped rGO) on the kinetics of HOR in alkaline media on these NiM/C catalysts.

A systematic methodology to determine what is limiting the performance of a fuel cell will be presented. The basis of this methodology is to utilize in-situ cell data combined with simple analytical techniques. The key analytical techniques are based on theoretically-predicted limiting cases for the different types of overpotential that can limit the performance of a polymer-electrolyte fuel cell (PEFC). These limiting cases are compared to PEFC performance data utilizing simple graphical techniques in order to provide semi-quantitative insight into the mechanisms primarily responsible for the cell polarization observed operating under the operating conditions of interest. This diagnostic methodology is ideally suited to investigate changes in the performance of a fuel cell. For example, the use of this methodology to investigate durability losses in PEFCs has been described [1]. However, the same techniques can be used to determine why the performance of one type of cell is different than a cell of a different configuration, or why the performance of a given cell varies with different operating conditions. Examples of each of these types of cell-performance investigations will be used to illustrate the methodology. The diagnostic method recommended here is a systematic, step-by-step method. The first step is to determine what major type(s) of overpotential are responsible for the changes in performance, namely: kinetic, ohmic, or mass transport. Polarization-change curves, such as those depicted in Figure 1, are a simple and useful tool to assist in apportioning performance changes to the different types of overpotential. The limiting cases depicted in Figure 1 were constructed with a relatively simple model of cell polarization [1]. These simple limiting cases, as well as some actual polarization-change curves examples, will be presented. Once the major types of overpotential have been identified, additional cell diagnostics can be selected to establish the sources (i.e., cell components and/or locations) of these changes. In-cell diagnostics for each of the major types of polarization are also recommended. For example, to determine whether mass-transport resistance is increasing within or external to the catalyst layer (or catalyst agglomerate) one can utilize an oxygen-gain analysis, which is based on a relatively simple model of the cathode potential and the two limiting cases predicted by this model [2]. To determine whether mass-transport losses are primarily due to oxygen transport and/or proton transport (i.e., ohmic losses in the catalyst layer), one can utilize an oxygen-dependence analysis, which is also based on limiting cases predicted by a simple model of the cathode [3]. The examples used to illustrate these diagnostic techniques will be on state-of-the-art PEFCs, so that the actual performance limitations being investigated should also be of interest to PEFC research community, such as mass-transport losses in PEFCs with ultra-low catalyst loadings. Acknowledgements Thanks to the organizers of this Symposia for the invitation to present. The author would also like to thank his many fuel-cell collaborators at United Technologies Corporation (both past and present). Funding from U.S. Department of Energy, EERE’s Fuel Cell Technologies Office under contract numbers DE-AC02-05CH11231 and DE-AC02-06CH11357 has enabled much of the recent work at UTRC on PEFCs that will be used as examples here, and is also gratefully acknowledged.