Performances Analysis of a PEMFC Supplied with Dry Air by Means of a Segmented Cell

For the use of polymer electrolyte membrane fuel cells (PEMFCs) in heavy duty applications, on-site generation of hydrogen rich gas by reforming hydrocarbons or methanol are a suitable alternative to pure H2 due to higher availability and higher energy density of hydrocarbon fuels [1]. The so-called reformate contains in addition of H2 also CO, which is a catalyst poison. PtRu alloys are the most promising catalysts for PEM fuel cells operated with reformate due to their high CO-tolerance [2]. It is known that the less noble Ru is unstable in acidic PEMFC conditions and is lowering the durability of the membrane electrode assembly (MEA) by dissolution and crossing over through the membrane to the cathode [3]. Ru dissolution and crossover result in a decreased CO-tolerance on the anode and a lower activity of the cathode towards oxygen reduction due to Ru blocking the Pt surface of the cathode catalyst [4]. To prolong the lifetime and CO-tolerance of reformate PEMFCs, the stability of the anode catalysts must be improved. One approach is nano-structuring the catalysts by encapsulating the less noble Ru-core with a Pt-shell. In doing so, the corrosion resistant Pt-shell supposes to protect the Ru-core from dissolution and thus mitigates the Ru crossover phenomenon.In this work, the influence of the Pt-shell thickness on the stability and performance of the Ru@Pt catalysts is investigated. Two catalysts with varying Pt-shell thicknesses were synthesized on Vulcan XC72R carbon via a two-step polyol. The catalyst with the thinner Pt-shell is called Ru@1Pt and with the thicker shell Ru@2Pt. The as-synthesized catalysts were physically characterized by XRD, ICP-OES, TEM and EDS. A representative EDS map of Ru@1Pt is shown in fig. 1a. The physical characterization of the obtained catalysts unveils a Ru@Pt core-shell structure with crystalline hcp Ru and fcc Pt. To further investigate the catalysts electrochemically, MEAs were manufactured using Ru@Pt catalysts as anodes and commercial membranes and cathode catalysts. An accelerated stress test (AST) was developed to target Ru dissolution by potential cycling and was applied to investigate and compare the stability of the catalysts. The MEAs were electrochemically characterized by cyclic voltammetry, CO-stripping and U-I curves before, during and after the AST. Post-mortem cross-section STEM analysis of the stressed cells were performed to evaluate the elemental composition and morphology of the anode and cathode after the stress test.During the AST, CO-stripping on the Ru@1Pt anode showed a peak shift to higher potentials, indicating a decrease in CO-tolerance due to Ru loss. By contrast, on the Ru@2Pt anode, the peak shifted to lower potentials implying a stronger promoting influence of Ru. On the cathode side, CV measurements before and after the AST revealed a double layer increase and a decrease in the HUPD. This change implies the poisoning of Pt with Ru and were more pronounced for Ru@1Pt compared to Ru@2Pt. As seen by the CO-stripping and CV results, the Ru dissolution and crossover was more severe for Ru@1Pt than for Ru@2Pt. Hence, a higher fuel cell performance loss was observed for the cell with Ru@1Pt in H2, as can be seen in fig. 1b. In addition, further U-I curves were measured under varying reformate conditions to identify the influence of CO on the cell performance. Cross-section EDS maps of the stressed MEAs were used to evaluate the Ru dissolution and its distribution in the different layers of the MEA. A higher Ru:Pt ratio was found on the cathode for the cell with Ru@1Pt compared to a cell with Ru@2Pt, which further verifies a higher degree of Ru crossover for the catalyst with the thinner Pt-shell. The above findings could evidence that the shell thickness plays a significant role in the corrosion resistance of core-shell reformate anode fuel cell catalysts.

In recent years, polymer electrolyte membrane fuel cells (PEMFCs) have garnered significant attention due to their remarkable attributes including high power density, energy efficiency, and zero-emission characteristics. This surge in interest has primarily been driven by the potential of PEMFC-powered fuel cell electric vehicles (FCEVs) to substantially reduce carbon dioxide emissions in the transportation sector, thereby propelling the advancement of the hydrogen economy on a global scale. However, the widespread commercialization of FCEVs hinges upon addressing key challenges surrounding the durability and resilience of fuel cell systems.One critical issue that has emerged is the phenomenon of hydrogen starvation in the anode, particularly during start-up/shutdown or cold start scenarios, which can lead to rapid and severe degradation of PEMFC performance and durability through cell reversal. This degradation manifests quickly, often within minutes, resulting in abrupt cell failure. Extensive prior research has been devoted to unraveling the mechanisms underlying degradation induced by hydrogen starvation and cell reversal in PEMFCs, with the goal of identifying effective mitigation strategies to minimize damage to membrane electrode assembly (MEA) components.In this study, we introduce an innovative materials approach aimed at mitigating cell damage by employing a thin film Pt anode catalyst supported on Nafion nanowires in a co-axial configuration, referred to as coaxial nanowire electrode (CANE). Leveraging the high roughness of Nafion nanowires, CANE eliminates the need for conventional carbon support and exhibits exceptional tolerance to reversal-induced stress. We present a comprehensive evaluation of CANE as a reversal-tolerant anode, comparing its performance to that of conventional supported catalysts (Pt/C). Furthermore, we explore the potential for further enhancing durability by integrating iridium with the CANE anode. Finally, we will delve into our efforts to evaluate the feasibility of implementing this concept in structures that can be manufactured at scale. This research contributes to the ongoing efforts to enhance the robustness and longevity of PEMFC systems, thereby advancing the prospects of FCEVs as a sustainable and viable solution for future transportation needs.AcknowledgementThis research was supported by the Hydrogen and Fuel Cell Technologies Office (HFTO), Office of Energy Efficiency and Renewable Energy, US Department of Energy (DOE) through the Million Mile Fuel Cell Truck (M2FCT) consortia, technology managers G. Kleen and D. Papageorgopoulos. Authors would also like to acknowledge support for this work from the Laboratory Directed Research and Development (LDRD) program at Los Alamos National Laboratory (LANL) (2020200DR).

State-of-the-art polymer electrolyte membrane fuel cells (PEMFC) cathode catalysts are platinum or platinum alloy nanoparticles loaded on a high surface area carbon support. Although these catalysts have been successfully implemented in passenger fuel-cell electric vehicles (FCEVs) (e.g., the Toyota Mirai), these catalysts are facing many performance and durability challenges that limit their applications in medium-duty and heavy-duty transportation. Among these challenges is the corrosion of the carbon support, which represents a source of efficiency loss (i.e., maximum voltages must be “clipped” to prevent catalyst degradation) and limitation of PEMFC lifetime. Corrosion of the carbon support affects catalyst utilization and the transport properties of the cathode as it can result in loss of electrical connection to the platinum alloy nanoparticles and destruction of electrode porosity.1-4 This talk introduces a new class of PEM fuel cell cathode catalyst supports called electron-conductive three-dimensional inorganic nanocrystals. The highly-conductive nanocrystals are fabricated by a chemical vapor deposition (CVD) assisted route using a home-built vertical plug-flow fused-quartz reactor. The developed synthesis method can produce gram scale amounts and operates in batch mode. Platinum nanoparticles have been introduced to the surface of newly- developed supports using different synthetic routes in order to demonstrate the excellent support durability after being subjected to different synthetic treatments. The ORR activity, catalyst performance durability, and catalyst support durability have been evaluated by means of the thin-film rotating disk electrode (TF-RDE) technique. The platinum content in the prepared catalysts has been measured using inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence (XRF). The morphology, crystal structure, and spatial distribution of the metal nanoparticles have been characterized by scanning electron microscopy (SEM) and scanning transmission electron microscopy (STEM), X-ray powder diffraction (XRD), and energy-dispersive X-ray spectroscopy (EDS), respectively. The electronic structure of the conductive 3-D inorganic nanocrystals has been identified by means of electron energy-loss spectroscopy (EELS), X-ray diffraction (XRD), and thermal gravimetric analysis (TGA) to be graphene-like with sp2 hybridized bonds.AcknowledgementsThis work was supported by the United States Department of Energy, Energy Efficiency and Renewable Energy, Hydrogen and Fuel Cell Technologies Office. Argonne is a U.S. Department of Energy Office of Science Laboratory operated under Contract No. DE-AC02-06CH11357 by UChicago Argonne, LLC.References F. Cetinbas, R. K. Ahluwalia, N. N. Kariuki, and D.J. Myers, J. Electrochem. Soc., 165(13), F1051 (2018).Kongkanand and M. F. Mathias, J. Phys. Chem. Lett., 7, 1127 (2016).Subbaraman, D. Strmcnik, A. P. Paulikas, V. R. Stamenkovic, and N. M. Markovic, Chemphyschem, 11, 2825 (2010).Cullen, David A., K. C. Neyerlin, Rajesh K. Ahluwalia, Rangachary Mukundan, Karren L. More, Rodney L. Borup, Adam Z. Weber, Deborah J. Myers, and Ahmet Kusoglu. "New roads and challenges for fuel cells in heavy-duty transportation." Nature Energy (2021): 1-13.

High-density storage of gases remains a major technological hurdle for many fields. The U.S. Department of Energy (DOE), for example, reduced their hydrogen storage targets for automotive applications due to the inability of technologies to reach the system-level targets.1 Without significant improvements in hydrogen storage density, hydrogen as a transportation fuel remains unfeasible. In other fields, the low volumetric and gravimetric storage densities of oxygen gas cylinders can be cumbersome or prohibitively expensive for applications like terrestrial and marine breathing apparatus’ or manned space exploration. Emerging technologies such as sorbents and chemical complexes show potential for gas storage. However, the ability to achieve application-specific gas delivery rates and high storage densities, while operating reversibly at ambient temperature, remains elusive.2, 3 In contrast, it may be possible to achieve high gas storage densities and potentially high gas delivery rates using nanocapillaries when used in conjunction with a membrane electrode assembly (MEA). Hoop stress calculations show that the pressure tolerances of cylinders are inversely proportional to the radius. Indeed, glass microcapillaries have already theoretically4 and experimentally5 demonstrated the capacity to achieve DOE hydrogen storage targets at a materials-level. This technology can be further improved by reducing the capillary radius to the nanoscale; however, the capping and pressurization of the gas in micro- or nanocapillaries remains problematic. Presented here is the fabrication of nanocapillary arrays capped by an MEA for highly reversible storage of gases with the potential for high rate pumping and high-density storage. Very high aspect ratio and densely packed nanocapillary arrays are produced through aluminum anodization. The nanocapillary arrays are capped with either a PEM or an alkaline (anion) exchange membrane (AEM) complete with catalyst nanoparticles on either side of the membrane to form an MEA. This MEA is used to provide controllable electrochemical pumping of hydrogen or oxygen gas into and out of the nanocapillaries. The MEA also serves as a high pressure seal. A theoretical discussion of the potential volumetric and gravimetric storage densities of hydrogen and oxygen in nanocapillary arrays will be presented together with experimental results of electrochemical gas compression into lab-scale devices. The evaluation of both commercial catalyst materials and fabricated nanoparticle catalysts (<10 nm) for hydrogen and oxygen pumping will be discussed. In addition, the performance of both PEM and AEM for electrochemical pumping of oxygen will be compared. A discussion of the electrochemistry within nanocapillaries compared to planar MEAs will be given including the charge transport/transfer processes. The potential failure mechanisms and the technical obstacles to the implementation of our electrochemical membrane approach, together with the current state of the technology and overall storage capacities, will be presented. 1. Hydrogen, Fuel Cells and Infrastructure Technologies Program: Multi-Year Research, Development and Demonstration Plan. US Department of Energy, Energy Efficiency and Renewable Energy 2012. 2. Zhou, L., Progress and problems in hydrogen storage methods. Renewable and Sustainable Energy Reviews 2005, 9 (4), 395-408. 3. Pukazhselvan, D.; Kumar, V.; Singh, S., High capacity hydrogen storage: basic aspects, new developments and milestones. Nano Energy 2012, 1 (4), 566-589. 4. Zhevago, N.; Glebov, V., Hydrogen storage in capillary arrays. Energy Conversion and Management 2007, 48 (5), 1554-1559. 5. Zhevago, N.; Denisov, E.; Glebov, V., Experimental investigation of hydrogen storage in capillary arrays. International Journal of Hydrogen Energy 2010, 35 (1), 169-175.

Within the last decades, fuel cells have become the center of attention of research community, industry, and the general public. This is due to the emphasis on the sustainability of the society and the emerging concept of a hydrogen economy. Proton exchange membrane fuel cells (PEM FCs) represent a mature and established fuel cell technology. The flexibility of operation, the high degree of fuel utilization, and the output power density make them suitable for mobile applications such as hydrogen-fueled vehicles or on-site energy generation. Membrane electrode assembly (MEA) is the mainstay of the PEM FCs. The MEA consists of the proton exchange membrane, catalytic layers, and gas diffusion layers (GDLs). Single MEAs are interconnected by bipolar plates with flow field channels homogenously distributing reactants and realizing easy removal of the generated water. Individual cells are compressed together, forming the fuel cell stack. The GDL plays a three-fold role in the performance of PEM fuel cells. It has to offer good electrical conductivity, ensure good reactant distribution along the reaction zone, and facilitate the removal of the water produced by the fuel cell operation. The optimal combination of these three aspects of GDL allows the FC to achieve high performance. Furthermore, the homogeneous distribution of the reactants is crucial for the durability and lifespan of the FC. The inhomogeneous reactants distribution leads to a local starvation of the electrode, leading to high local overvoltage and thus shortening the lifespan of overloaded parts. Although GDLs play a crucial role in the operation of PEM fuel cells, so far, they have received little attention. Hence, the objective of our study is to compare commercially available GDLs with respect to their properties, namely permeability under conditions close to the operating fuel cell.The approach of combining advanced mathematical modeling with extensive experimental characterization was used to achieve this task. Testing cells allowing precise determination of the in-plane permeability of various GDLs were designed based on the computational fluid dynamics modeling. According to the contemporary literature, two different carbon based GDLs were examined, namely carbon-cloth and carbon-paper, which principally differ in the carbon-fiber orientation in their internal structure. The investigated properties of GDLs thus include thickness, porosity, internal structure, and the presence or absence of microporous layer.The achieved experimental results show that at given compression, thicker carbon paper GDLs are superior to carbon cloth samples in terms of permeability and deformation resistance. The obtained permeability values of GLDs at different degrees of compression were compared with predictions based on the Carman-Kozeny equation to assess the accuracy of this semi-empirical prediction. Finally, the importance of the optimal flow field and GDL combination in terms of reactant distribution in the fuel cell stack of industrial conditions is documented via mathematical modelling based on the obtained experimental data.This work was supported by the European Regional Development Fund-Project “Fuel Cells with Low Platinum Content” (No. CZ.02.1.01/0.0/0.0/16_025/0007414).

Recently, the polymer electrolyte membrane fuel cells (PEMFCs) have attracted the great attention as energy conversion devices for powertrain for the fuel cell electric vehicle and a residential combined heat and power system due to the zero-emission of harmful gas and high energy efficiency. To overcome of the drawbacks of perfluorosulfonic acid (PFSA) membrane and Pt poisoning by CO, the high-temperature PEMFC (HT-PEMFC) has been developing over decades, which has significant advantages as compared to low-temperature PEMFC (LT-PEMFC). For example, it has a much better fuel tolerance, enhanced the reaction kinetics and a simple water management [1,2]. However, the practical power density of membrane electrode assembly (MEA) for HT-PEMFC is much lower than that of LT-PEMFC because of the huge activation loss by acid poisoning [3–5]. Thus, a large amount of Pt is required in the electrode to ensure the sufficient power and long-term durability, which is a critical issue for HT-PEMFC. Therefore, one of the most critical issue for the HT-PEMFC is the decreasing the Pt amount in the electrode without sacrificing the MEA performance [5]. In addition, the fabrication of electrode using the advanced supported catalyst is the very important topic for revealing the improved catalytic activity into performance of MEA [2,5]. In this study, various formulation parameters for making the catalyst slurry using ball-milling were investigated to obtain the smooth electrode for MEA. The parameters are the presence of a viscosity agent, the solid content, and the amount of binder for the MEA of HT-PEMFC. When the viscosity agent is added in the 2.5 wt.% in the catalyst slurry, the slurry is very suitable for making a coated electrode on the gas diffusion layer (GDL). On the contrary, while when the amount of viscosity agent is increased over than 5 wt.%, the electrode is not completely dried. The optimum solid content of catalyst in the slurry was determined in the range of 12 wt.% because if the amount of catalyst exceeded the 14wt.%, the electrode is peeled off severely after drying. The open circuit voltage and performance of MEA under HT-PEMFC condition is depended significantly on the amount of polyvinylidene fluoride (PVDF) in the catalyst slurry. The voltage at a very small current density at 0.008A/cm2 of MEAs with different amount of PVDF was decreased from 0.775 to 0.735 V by increasing the 10wt.% to 30 wt.% of PVDF, which provide the increase of the activation overpotential by poisoning of phosphoric acid on the Pt catalyst. However, the performance of MEA at 0.6A/cm2 was maximized as 0.44 V at the 30wt.% of PVDF in the catalyst slurry, which suggests that the Ohmic overpotential decreased with increasing the PVDF amount. In summary, for maximizing the MEA performance under HT-PEMFC at 150℃, the various conditions for the manufulation of electrode was invesitgated. The amount of PVDF has a significant effect on the performance of MEA. [1] J. Zhang, Y. Xiang, S. Lu, and S. P. Jiang, Adv. Sustainable Syst. 2, 1700184 (2018). [2] D. J. You, D. H. Kim, J. R. De Liled, C. Li, S. G Lee, J. M. Kim, and C. Pak, Appl. Catal. A: General 562, 250–257 (2018). [3] R. E. Rosli, A. B. Sulong, W. R. W. Daud, M. A. Zulkifley, T. Husaini, M. I. Rosli, E. H. Majlan, and M. A. Haque, Int. J. Hydrogen Energy 42, 9293–9314 (2017). [4] A. Chandan, M. Hattenberger, A. El-kharouf, S. Du, A. Dhir, V. Self, B. G. Pollet, A. Ingram, and W. Bujalski, J. Power Sources 231, 264–278 (2013). [5] S.-W. Choi, J. O. Park, C. Pak, K.H. Choi, J.-C. Lee, and H. Chang, Polymers 5, 77–111 (2013).

The proper integration of materials to enable high performing low temperature fuel cell operation has never been more crucial to realizing the isolated (e.g. half-cell or ex-situ) improvements of advanced electrocatalysts, supports and ionomers in an effort to maximize efficiency. The integration pathway for oxygen reduction electrocatalysts, from initial testing in a rotating disk electrode (RDE) to their apex form as porous electrodes in a membrane electrode assembly (MEA) is replete with potential pitfalls. Along the route to improving MEA level electrocatalyst kinetics and electrode transport properties are numerous choices relating to ink formulation (i.e. solvents and solvent ratios), ink processing and deposition methodology, ionomer content and chemistry and electrochemical MEA conditioning. Combined with carbon morphology/porosity, such variables can alter the final electrode morphology, influencing active site accessibility and ORR activity as well as oxygen transport resistance and electrode proton conductivity.[1–5]Here, the development and utilization of in situ diagnostics designed to probe specific phenomena (e.g. catalyst/ionomer interactions, molecular and Knudsen diffusion, electrochemical active site accessibility and catalyst layer proton resistance) will be presented as tools to contrast the ink, processing and fabrication methods necessary to achieve high performance PGM (e.g. Pt/C and Pt alloy/C) and PGM-free (e.g. FeNx/C) electrocatalysts based electrodes. For PGM based MEAs, the dynamic effects of electrochemical conditioning will be examined in an effort to both baseline MEA level performance and decouple the contributions of simultaneous electrocatalyst particle growth and the removal of system impurities.[6] The prerequisite understanding gleaned from the application of electrochemical diagnostics and MEA conditioning procedures will be combined with the development of a novel sulfonated ionic liquid block copolymer ionomer and tailored integration methodology to illustrate a pathway towards improved MEA level performance.[7] Lastly, alterations in ionomer interactions as a function of accelerated stress tests will be discussed, providing insight into the evolving electrode structure as the community targets more robust systems capable of efficient operation for 25,000 hrs.[8]References[1] A. Orfanidi, P.J. Rheinlander, N. Schulte, H.A. Gasteiger, Ink Solvent Dependence of the Ionomer Distribution in the Catalyst Layer of a PEMFC, Journal of The Electrochemical Society. (2018) 11.[2] S. Khandavalli, J.H. Park, N.N. Kariuki, D.J. Myers, J.J. Stickel, K. Hurst, K.C. Neyerlin, M. Ulsh, S.A. Mauger, Rheological Investigation on the Microstructure of Fuel Cell Catalyst Inks, ACS Appl. Mater. Interfaces. (2018) 13.[3] D.A. Cullen, R. Koestner, R.S. Kukreja, Z.Y. Liu, S. Minko, O. Trotsenko, A. Tokarev, L. Guetaz, H.M. Meyer, C.M. Parish, K.L. More, Imaging and Microanalysis of Thin Ionomer Layers by Scanning Transmission Electron Microscopy, J. Electrochem. Soc. 161 (2014) F1111–F1117. https://doi.org/10.1149/2.1091410jes.[4] T. Van Cleve, S. Khandavalli, A. Chowdhury, S. Medina, S. Pylypenko, M. Wang, K.L. More, N. Kariuki, D.J. Myers, A.Z. Weber, S.A. Mauger, M. Ulsh, K.C. Neyerlin, Dictating Pt-Based Electrocatalyst Performance in Polymer Electrolyte Fuel Cells, from Formulation to Application, ACS Appl. Mater. Interfaces. 11 (2019) 46953–46964. https://doi.org/10.1021/acsami.9b17614.[5] G. Wang, L. Osmieri, A.G. Star, J. Pfeilsticker, K.C. Neyerlin, Elucidating the Role of Ionomer in the Performance of Platinum Group Metal-free Catalyst Layer via in situ Electrochemical Diagnostics, J. Electrochem. Soc. 167 (2020) 044519. https://doi.org/10.1149/1945-7111/ab7aa1.[6] S. Kabir, D.J. Myers, N. Kariuki, J. Park, G. Wang, A. Baker, N. Macauley, R. Mukundan, K.L. More, K.C. Neyerlin, Elucidating the Dynamic Nature of Fuel Cell Electrodes as a Function of Conditioning: An ex Situ Material Characterization and in Situ Electrochemical Diagnostic Study, ACS Appl. Mater. Interfaces. 11 (2019) 45016–45030. https://doi.org/10.1021/acsami.9b11365.[7] Y. Li, T.V. Cleve, R. Sun, R. Gawas, G. Wang, M. Tang, Y.A. Elabd, J. Snyder, K.C. Neyerlin, Modifying the Electrocatalyst−Ionomer Interface via Sulfonated Poly(ionic liquid) Block Copolymers to Enable High- Performance Polymer Electrolyte Fuel Cells, ACS Energy Letters. (2020) 6.[8] D.A. Cullen, K.C. Neyerlin, R.K. Ahluwalia, R. Mukundan, K.L. More, R.L. Borup, A.Z. Weber, D.J. Myers, A. Kusoglu, New roads and challenges for fuel cells in heavy-duty transportation, Nature Energy. (2021) 1–13. https://doi.org/10.1038/s41560-021-00775-z.

The maturity of the current polymer electrolyte membrane fuel cells (PEMFCs) has been product of the considerable scientific and industrial effort devoted to developing highly efficient and reliable versions of this technology, resulting in its increased application in the transportation and energy generation sectors. Fuel cells are one of the most advantageous solutions for clean energy applications due to their near-zero-emission, high efficiency, low maintenance cost, and high energy density. PEMFCs produce electricity through the electrochemical reaction of hydrogen and oxygen (or air) taking place in the Membrane Electrode Assembly (MEA) by converting chemical energy of the hydrogen oxidation and oxygen reduction into electrical energy with water as a byproduct. However, producing oxygen reduction reaction (ORR) catalysts with high performance at scale is still a challenge that needs to be tackled to enable an increment in energy generation of this technology. Additionally, tunability of the materials at the core of this technology is essential to meet the demands of the specific application and operating conditions. Here we investigate commercially available ORR catalysts based on platinum nanoparticles (Pt-NPs) supported on nitrogen-functionalized carbon (Engineered Carbon SupportsTM, ECSTM) produced by Pajarito Powder, LLC at scale. The ORR performance of three MEAs made with different Pt/ECS catalysts, by IRD Fuel Cells, LLC was studied under low relative humidity conditions, exhibiting competitive performance, and reaching current densities between 1.8 and 1.3 A/cm2 at 0.6 V, at extremely low loading of Pt – 0.1 mgPt cm-2. The physicochemical properties of these Pt/ECS catalysts alongside their Pt-free ECSTM analogue carbon support materials were comprehensively studied. For this purpose, several characterization techniques were used, such: X-ray diffraction, Raman spectroscopy, and transmission electron microscopy (TEM) to investigate structural and morphological properties, X-ray photoelectron spectroscopy to determine the surface composition and chemical properties, thermogravimetric analysis to evaluate thermal oxidation properties, and nitrogen sorption to determine the surface area and porosity, of the materials. This thorough characterization enabled us to determine that the best performing catalyst in the conditions used in this work have the highest surface area and the highest concentration of surface dopants (nitrogen and oxygen). Although, catalyst supported on lower surface area carbon, but with higher graphitic content, also exhibited competitive performance that can be exploited in applications where more corrosion-resistant carbon is needed. Finally, based on the highly competitive MEA performance for the three Pt/ECS catalysts supported on these carbons, our work demonstrates that these carbon supports (developed by Pajarito Powder, LLC) with engineered morphology and composition fabricated through VariPoreTM synthetic technology can result in tunable properties suitable for a targeted application. We can conclude that these commercially available materials can be adapted through modification of the versatile synthesis platform to tune the physiochemical properties of carbons for other applications and conditions.

Maximizing the energy density of a portable power system is an important design factor since those systems have stringent maximum mass constraints. While Lithium-ion batteries are currently the standard choice for power systems in the scale of 10-100 watts, direct hydrocarbon Proton-exchange membrane fuel cells (PEMFC) have the potential to be more energy-dense than batteries at those scales even with efficiencies as low as %10. PEMFC are simple and operate at low temperatures which make them a suitable choice for portable power generation. Because of their low operating temperature, they are usually fueled by hydrogen. However, hydrogen is hard to store and handle, which makes it an unsuitable fuel for portable power applications. Alternatively, Hydrocarbon fuels, such as butane, are easier to store and safer to handle. Additionally, hydrocarbon fuels are ~50 times more energy dense than state of the art Lithium-ion batteries. For those reasons, it is desirable to develop a direct butane PEMFC for portable power applications. Limited work has been done in the past to demonstrate the viability of direct butane fuel cells, mainly because of the low reactivity of hydrocarbon in low temperature PEMFC. EH Kong et. al. demonstrated a working direct butane PEMFC by adding trace amounts of unsaturated hydrocarbons to the butane and operating the cell in “load-interrupt” mode. The authors proposed that butane might be converting active catalyst sites to inactive sites, causing the fuel cell to ‘extinguish’. Thus, the addition of unsaturated hydrocarbons and the load-interrupt operating mode can circumcise this saturation process. In this work, we demonstrate the repeatability of the direct butane PEMFC results produced by EH Kong et. al. on a custom-built fuel cell testing apparatus and explore methods to explain the current dynamics of the cell.For the experimental setup, we used a 25cm2 membrane electrode assembly (MEA). It consisted of treated Nafion N-177 layer directly painted with a catalyst layer on the anode and cathode sides. The catalyst layer is obtained from an ink that is prepared by mixing platinumblack, water, and 5% Nafionsolution. The Nafion N-177 layer is prepared using the manufacturer standard pretreatment procedure. Once assembled, the MEA layer is then pressed at 120 °C and 500 lbs. for 25 min. We then load the MEA layer into the fuel cell hardware, which includes the fuel cell, humidifiers, and heaters, and test the cell electrical performance at temperatures below (100C).Using the fuel cell testing apparatus, we confirm that for high purity butane (>%99.99) the PEMFC does not start and no open circuit voltage is detected. However, the PEMFC is started when unsaturated hydrocarbons are added to the butane fuel stream as shown in previous work. Specifically, the addition of ethylene at concentrations of 2000 ppm allows the PEMFC to operate continuously at low temperatures (<100C). Previously observed current dynamics were also reproduced. The current density of the fuel cell peaks in the beginning of the cell operation and decreases over time until it reaches steady state. It was observed that operating the cell in a load-interrupt mode, where the current is set to zero for 5 seconds every 25 second of operation, increases the average power density of the cell, when compared to the galvanostatic operating mode. Further we investigate the effect of different additives to butane. Specifically, we explore the effect of adding different concentration of hydrogen to the butane stream to analyze whether the interaction between the two fuels is independent or synergetic. Furthermore, we produce Electrochemical Impedance spectrums of the direct butane PEMFC to gain insights about cell resistances including mass transport limitations.For future work, we are interested in in-situ measurement techniques that allow us to observe the intermediates on the catalyst surface. Such data might allow us to verify and inform the empirical dynamical model proposed in previous work to explain the direct butane PEMFC current dynamics.

This paper summarizes some of the progress that has been made over the past 30 years in identifying chemical and mechanical degradation mechanisms in proton-exchange membrane fuel cells (PEMFCs), as well as approaches in refining stack operating conditions, cell hardware configurations and membrane- electrode assembly (MEA) stabilization to mitigate degradation and extend life. New analytical methods have been brought to bear to understand the relationships between PEM degradation and fuel cell operating conditions, especially low relative humidity, elevated temperatures, and frequent open-circuit periods. PEM/MEA degradation similar to that observed in PEMFC may also occur under certain accelerating conditions for proton-exchange membrane water electrolyzers (PEMELCs) that typically operate for 30 to 100 thousand hours without incident when properly hydrated, thermally managed and mechanically supported. A comparison is made of common hardware and operational factors for PEMELCs and PEMFCs that can lead to PEM/MEA degradation.

The membrane electrode assembly (MEA) encompassing the polymer electrolyte membrane (PEM) and catalyst layers are the key components in Polymer Electrolyte Membrane Fuel Cells (PEMFCs). The cost of the PEMFC stacks has been limiting its commercialization due to the inflated price of conventional platinum (Pt)-based catalysts. As a consequence, the authors of this paper focus on developing novel bi-metallic (Pt-Co) nano-alloy-catalyzed MEAs using the non-equilibrium impregnation–reduction (NEIR) approach with an aim to reduce the Pt content, and hence, the cost. Herein, the MEAs are fabricated on a Nafion® membrane with a 0.4 mgPtcm−2 Pt:Co electrocatalyst loading at three atomic ratios, viz., 90:10, 70:30, and 50:50. The High Resolution-Scanning Electron Microscopic (HR-SEM) characterization of the MEAs show a favorable surface morphology with a uniform distribution of Pt-Co alloy particles with an average size of about 15–25 µm. Under standard fuel cell test conditions, an MEA with a 50:50 atomic ratio of Pt:Co exhibited a peak power density of 0.879 Wcm−2 for H2/O2 and 0.727 Wcm−2 for H2/air systems. The X-ray diffractometry (XRD), SEM, EDX, Cyclic Voltammetry (CV), impedance, and polarization studies validate that Pt:Co can be a potential affordable alternative to high-cost Pt. Additionally, a high degree of stability in the fuel cell performance was also demonstrated with Pt50:Co50.

The membrane electrolyte assembly (MEA) is the key component of a proton exchange membrane fuel cell (PEMFC). The MEA usually consists of gas diffusion layers as outer layers to the inner catalyst coated membrane (CCM). There are various methods to prepare CCMs and decal transfer is currently a common method which was first introduced by Wilson and Gottesfeld [1] and further developed by other researchers [2]–[4]. The initial step of this method is that the catalyst ink is coated onto an intermediate substrate material creating a catalyst coated film (CCF). This step is followed by a transfer of the active layer onto the membrane by hot pressing the membrane and CCF between heated press platens maintained at a specific high temperature for an optimized time and pressure to ensure bonding.Extensive studies on the procedure of decal transfer, substrate material and its preparation, catalyst solvents, etc. have increased the transfer yield of decal transfer to more than 95% [5]. Additionally, in the last decade, industrial development has reduced its cost; however, the total cost for fuel cell manufacturing is still relatively high. One reason for this high production cost is the contamination sensitivity of the CCMs by external particles that can potentially be detrimental to fuel cell operation [6]. This requirement necessitates the use of cleanrooms and quality control equipment to prevent contaminants entering the manufactured components, thus increasing the overall costs. The purpose of the present research is to improve the understanding of the interactions between foreign contaminants and the manufacturing process in the context of MEA production quality. The specific objectives are to i) understand the impact of external particles on the catalyst layer decal transfer process and ii) improve the robustness of the decal transfer method in the presence of external particles.This research investigates the impact of incidental external particles that may be found on the membrane surface or the CCF prior to hot pressing. 60µm Silica microspheres (Si-M) were selected as a representative of solid particles and CCMs with purposely introduced Si-Ms were fabricated and several decal transfer methods and support materials were tested and imaged using the X-ray computed tomography (XCT) technique to analyze the impact on the fuel cell integrity and operation at the presence of the Si-M. While regular decal transfer protocols result in excessive membrane thinning in the presence of these particles, it was observed that by changing the rate of applied pressure and using alternative support materials when transferring the cathode catalyst onto a half-coated membrane, it was possible to reduce membrane thinning under the particles by more than 20% while maintaining transfer quality and cell performance (Fig. 1). In addition, it was observed that although anisotropic mechanical properties of the membrane can adversely affect the CCM topography after the decal transfer, a tuned protocol is able to prevent unwanted deformations and potential stress concentrations. Overall, it is envisioned that the outcomes of this work may enable relaxed quality control measures and manufacturing site cleanroom standards by reducing the potential effects of external particles on MEA production quality. Acknowledgements This research was supported by the Natural Sciences and Engineering Research Council of Canada, Canada Foundation for Innovation, British Columbia Knowledge Development Fund, Western Economic Diversification Canada, Ballard Power Systems, and W.L. Gore & Associates. This research was undertaken, in part, thanks to funding from the Canada Research Chairs program. Keywords: fuel cell; membrane durability; X-ray computed tomography; decal transfer; manufacturing References Wilson, M. S. & Gottesfeld, S. Thin-film catalyst layers for polymer electrolyte fuel cell electrodes. J. Appl. Electrochem. 22, 1–7 (1992).Shahgaldi, S., Alaefour, I. & Li, X. Impact of manufacturing processes on proton exchange membrane fuel cell performance. Appl. Energy 225, 1022–1032 (2018).Cho, H. J. et al. Development of a novel decal transfer process for fabrication of high-performance and reliable membrane electrode assemblies for PEMFCs. Int. J. Hydrogen Energy 36, 12465–12473 (2011).Thanasilp, S. & Hunsom, M. Effect of MEA fabrication techniques on the cell performance of Pt-Pd/C electrocatalyst for oxygen reduction in PEM fuel cell. Fuel 89, 3847–3852 (2010).Liang, X., Pan, G., Xu, L. & Wang, J. A modified decal method for preparing the membrane electrode assembly of proton exchange membrane fuel cells. Fuel 139, 393–400 (2015).James, B. D., Moton, J. M. & Colella, W. G. Mass Production Cost Estimation of Direct H2 PEM Fuel Cell Systems for Transportation Applications: 2018 Update. ASME 2014 12th Int. Conf. Fuel Cell Sci. Eng. Technol. collocated with ASME 2014 8th Int. Conf. Energy Sustain. V001T07A002–V001T07A002 (2018). Figure 1

Challenges and opportunities in modelling of proton exchange membrane fuel cells (PEMFC)

The water dynamics of the membrane electrode assembly (MEA) of a 50 cm2 polymer electrolyte membrane (PEM) fuel cell was studied in response to current and humidity step transients as a function of inlet relative humidity (RH) and cell operating temperature. MEA water content change was monitored by high frequency resistance (HFR) and in situ neutron imaging. The MEA "wetting" response was significantly faster (10-30 seconds) than the reciprocal "drying" response (several minutes). The wetting response to increasing current appears faster than that to increasing gas inlet RH. Wetting and drying responses to gas inlet RH transients are greater at low current densities showing the dominating effect of current wetting over gas inlet humidity effects. Operating the fuel cell at 40oC with no inlet gas humidification, a current wetting response was observed and 34 amps of current sustained. This showed that reaction water produced at the cathode is sufficient to support high current density if the drying effect of inlet gases is low. It also suggests that back diffusion of reaction water to the MEA is sufficient to account for the fast drop in HFR. In situ neutron imaging results show that GDL wetting is also faster than drying but on a slower time scale than that for the MEA. However, MEA and GDL drying are on a similar slow time scale and are coupled because water diffusing out of the MEA must move through the GDLs.

The most promising alternative to Platinum Group Metals (PGMs) Oxygen Reduction Reaction (ORR) catalysts for proton exchange membrane fuel cell (PEMFC) applications is a class of electrocatalysts consisting of atomically dispersed transition metals (Fe and Mn) in a matrix of carbon and nitrogen, so called M-N-C materials [1]. Currently, the emerging novel M-N-C materials demonstrated 30% of PGM catalyst activity [1]. Performance of PGM-free electrocatalysts can be improved by increasing density of M-Nx sites or optimizing their accessibility through proper integration into the triple phase catalyst layer in a membrane electrode assembly (MEA). Since overall MEA’s performance depends on properties of all its components: membrane, electrodes and gas diffusion layers (GDL), it is important to understand impact of these materials on PGM-free fuel cell operation. In this work we report effects of membrane thickness on performance of PGM-free PEMFCs using various electrochemical methods and modelling.The commercial, PGM-free electrocatalyst manufactured by Pajarito Powder and marketed as PMF-011904 was used in the present study. Catalyst coated membranes with active area of 23 cm2 were manufactured by IRD Fuel Cell by their proprietary digital printing method. For this work we used membranes with thickness of 15 (LYT0008), 25 (N211), 125 (N115) and 175 (N117) μm. The cathode PGM-free catalyst loading was 6.0 mg cm-2, while anode employed Pt/C catalyst with loading of 0.2 mgPt cm-2. Freudenberg H23C8 GDLs were applied for both electrodes. Electrochemical evaluation of PGM–free MEAs was performed using a custom test station, designed at the HNEI and characterized by dynamic response time <0.1 s. The anode and cathode were fed with H2 and O2 respectively, at constant flow rates of 0.5 slpm at 100% relative humidity and 150 kPa absolute backpressure for both electrodes, and the cell temperature was 80°C.Fig. 1 a) shows a representative SEM image of the MEA cross-section. The cathode thickness was found to be 140-160 μm for all samples. The IV data clearly showed that an increase in the membrane thickness led to an increase of HFR and caused poor performance (Fig. 1 b). The highest performance was achieved for MEAs with thin membranes 15 and 25 μm. At the same time application of thick membrane allowed us to reach the highest ocv values 0.979 V (175 μm) vs 0.929 V (15 μm). The impedance data were analyzed using physics-based model which includes proton and oxygen transport in the cathode layer [2]. The results demonstrated a rapid decay of proton conductivity from 15-18 to 5-10 mS cm-1 at current densities higher than 100 mA cm-2. Possible mechanism of the observed decay can be attributed to dissolution of Fe-N-C centers and formation of Fe3+ cations which reduce ionomer conductivity by screening SO3- groups [3-4].Due to relatively low proton conductivity and large electrode thickness, the ORR rate is strongly non–uniform through the cathode depth. Our estimates showed that this non-uniformity leads to 2 K overheat of the catalyst layer at the membrane surface. The overheat could induce pressure gradient, pushing liquid water out of the electrode and clearing void pores for gaseous transport of oxygen. This mechanism might explain explosive growth of the cathode oxygen diffusivity (5-7⋅10-3 cm2 s-1). Detailed analyses of the PGM-free PEMFC performance and its correlation with AC-impedance results will be presented and discussed.AcknowledgmentsWe gratefully acknowledge funding from ONR (N00014-19-1-2159) and DOE EERE (DE-EE0008419). The authors are thankful to T. Carvalho for assisting with SEM.Reference1. S.T. Thompson, A.R. Wilson, P. Zelenay, D.J. Myers, K.L. More, K.C. Neyerlin, D. Papageorgopoulos, Solid State Ionics 319, 68-69 (2018).2. A. Kulikovsky, J. Electroanal. Chem. 669, 28-34 (2012).3. T. Reshetenko, G. Randolf, M. Odgaard, B. Zulevi, A. Serov, A. Kulikovsky, J. Electrochem. Soc. 167, 084501 (2020).4. T. Reshetenko, A. Serov, A. Kulikovsky, P. Atanassov, J. Electrochem. Soc. 166, F653-F660 (2019). Figure 1