Modelling and validation of Proton exchange membrane fuel cell (PEMFC)

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

Proton exchange membrane (PEM) fuel cells have gained increasing interest from academia and industry, due to its remarkable advantages including high efficiency, high energy density, high power density, and fast refueling, also because of the urgent demand for clean and renewable energy. One of the biggest challenges for PEM fuel cell technology is the high cost, attributed to the use of precious platinum group metals (PGM), e.g., Pt, particularly at cathodes where sluggish oxygen reduction reaction takes place. Two primary ways have been paved to address this cost challenge: one named low-loading PGM-based catalysts and another one is non-precious metal-based or PGM-free catalysts. Particularly for the PGM-free catalysts, tremendous efforts have been made to improve the performance and durability—milestones have been achieved in the corresponding PEM fuel cells. Even though the current status is still far from meeting the expectations. More efforts are thus required to further research and develop the desired PGM-free catalysts for cathodes in PEM fuel cells. Herein, this paper discusses the most recent progress of PGM-free catalysts and their applications in the practical membrane electrolyte assembly and PEM fuel cells. The most promising directions for future research and development are pointed out in terms of enhancing the intrinsic activity, reducing the degradation, as well as the study at the level of fuel cell stacks.

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.

The regulation of reactants pressure and supply are prerequisite for the performance and prolong life of Proton Exchange Membrane Fuel Cell (PEMFC). The depleted supply of reactants may deteriorate the operation of PEMFC. Moreover, the large deviation of reactants pressure can cause severe damage to the stack. The main aim of this paper is to control the pressure of hydrogen at anode and oxygen at cathode side by maintaining hydrogen and oxygen flow rates at optimum levels during dynamic load conditions. Sliding Mode Controller (SMC) is employed to control the reactants pressure at set point under dynamic load change. The results reveal that SMC employed in PEMFC produce better response than the PI controller reported earlier.

In the recent years, by increasing the consumption of fossil fuels, the carbon dioxide level increases, which affects human health and climate change. One of the important technologies to solve these problems is fuel cell vehicles (FCVs), and, due to low operating temperature and high efficiency, the proton exchange membrane fuel cells (PEMFCs) have been more considered among various types of FCVs. Computational fluid dynamics (CFD) and numerical modeling have a great potential to study the detailed physical phenomena in the fuel cells such as mass, heat and energy transport, electrode kinetics, and potential fields and can reveal which factors in a real system are most important from a sensitivity point of view We reviewed several existing works relevant to CFD simulation and mathematical modeling of PEMFCs, which were performed by different software and codes like ANSYS Fluent, COMSOL, lattice Boltzmann, MATLAB codes, and OpenFOAM. The key factors that affect performance and failure modes of PEMFCs were discussed based on these simulations. One of these factors is water management that can be improved by using appropriate flow field configuration. The various configurations were reviewed. In addition, the effect of humidification of inlet reactants on the performance of PEMFCs was discussed.

Imaging PEMFC performance heterogeneity by sensing external magnetic field

The activation of oxygen in fuel cells and generally in electrocatalytic processes is of paramount importance to make such technologies marketable. For this reason it has been extensively studied for the last fifty years [1]. It is known that platinum-based binary alloys are excellent catalysts for the ORR (oxygen reduction reaction), which occurs at the cathode of PEMFCs (proton exchange membrane fuel cells). Beyond the lowering of the platinum loading in the electrode catalytic layers, alloyed Pt-based materials lead to the improvement of the catalytic activity [2], to the increase of the tolerance towards poisoning species and, for some authors, to durability enhancement of the catalysts under fuel cell working conditions [3]. PtxM1-x bimetallic materials (M = Co, Fe, Ni and Cr) have been extensively studied in order to correlate their catalytic activity and their electrochemical stability towards the ORR to their composition, crystallographic and electronic structures. Recent works have clearly shown that commercial Pt3Co/C nanoparticles were not totally stable during PEMFC operation even if they were more stable than monometallic Pt/C catalysts, they suffered compositional changes at the nanoscale.Other noble metals were also considered for the activation of the ORR in acidic medium, such as palladium and gold. Amongst pure metals, palladium leads to the highest activity towards the ORR, just after platinum. A review paper of Antolini [4] cited numerous publications explaining that palladium-based alloys or core-shell structures could lead to activities towards the ORR higher than those observed on pure palladium, and almost comparable to those recorded on pure platinum. Pd-Co and Pd-Fe are the most cited metallic alloys because they are the most active, in agreement with DFT (Density Functional Theory) calculations. Recently, PtPd alloys with very low Pt atomic ratio led to remarkable fuel cell electric performances [5]. Bimetallic PtxAu1-x catalysts have also led to excellent stability and activity under PEMFC working conditions, making this kind of materials a serious alternative candidate to platinum as cathode electrocatalysts in a PEMFC.In comparison, few studies have been carried out on the behavior of trimetallic catalysts towards the ORR. PtFeNi nanoparticles showed excellent electrocatalytic performances under PEMFC working conditions [6]. The research group of Manthiram studied Palladium-based trimetallic catalysts. They obtained activities towards the ORR comparable or even slightly higher to that of a Pt/C catalyst using Pd–Co–Mo/C and Pd–Co–Au/C materials. Although a few studies on trimetallic catalyst activity and stability is available in the literature, several trends could be drawn : (i) alloying platinum with a less noble metal seems to be beneficial for the ORR in terms of activity and tolerance, (ii) the interactions between two different noble metals such as Pt-Pd, Pt-Au and Au-Pd seems to enhance the durability and the catalytic activity towards the ORR with respect to pure metals and (iii) platinum seems unavoidable in order to achieve the best possible activity from the catalyst in an acidic environment. So in the present work, the synthesis and characterization of carbon supported Pt, Pd and Au based binary and ternary catalysts (PtxPdyAuz/C) are described as well as their systematic study (activity and selectivity) towards the ORR. The aim of this work is to allow defining a relevant catalyst formulation (composition and atomic ratio) for enhanced ORR performance. Acknowledgement: The financial support of the European Commission under the FP7 Fuel Cells and Hydrogen Joint Technology Initiative grant agreement FP7-2012-JTI-FCH-325327 for the SMARTCat project is gratefully acknowledged.[1] C. Coutanceau, S. Baranton, “Advanced Processes in Catalytic Oxidation - Oxygen Activation in Fuel Cells and Electrocatalytic Processes”, in “From Laboratory Studies to Industrial Applications", D. Duprez and F. Cavani (Eds.), Imperial College Press, London, 2014.[2] M. T. Paffet, J. G. Beery, S. Gottesfeld, Oxygen reduction at Pt0.65Cr0.35, Pt0.2Cr0.8 and roughened platinum J. Electrochem. Soc. 135 (1988) 1431-1436.[3] X.Yu, S.Ye. Recent advances in activity and durability enhancement of Pt/C catalytic cathode in PEMFC: Part II: Degradation mechanism and durability enhancement of carbon supported platinum catalyst, J. Power Sources 172 (2007) 145-154.[4] E. Antolini, Palladium in fuel cell catalysis, Energy Environ. Sci. 2 (2009) 915-931.[5] M. Mougenot, A. Caillard, P. Brault, S. Baranton, C. Coutanceau, High Performance Plasma Sputtered PdPt Fuel Cell Electrodes with Ultra Low Loading, Int. J. hydrogen Energy 36 (2011) 5429-8434.[6] B. Fang, B. N. Wanjala, J. Yin, R. Loukrakpam, J. Luo, X. Hu, Jo. Last, C.-J. Zhong, Electrocatalytic performance of Pt-based trimetallic alloy nanoparticle catalysts in proton exchange membrane fuel cells, Int. J. Hydrogen Energy 37 (2011) 4627–4632

Performance analysis of PEM fuel cell in mobile application under real traffic and environmental conditions

Nowadays, with increasing energy requirements, the use of clean energy resources has become important. Fuel cells are an important key for clean energy technology due to wide range of utilization areas such as automotive, portable power applications, electricity generation, space, aviation and naval technologies. Additionally, they have many significant properties such as not producing harmful gases, therefore they do not cause environmental and chemical pollution. Besides, they have not any moving parts, also they do not produce noise. By comparison to fossil fuel, fuel cells have high efficiency that reaches up to 60% in appropriate conditions. Proton Exchange Membrane Fuel Cell (PEMFC) has many advantages than other fuel cell types due to simple structure, higher efficiency and low operating temperature. PEMFC may consist of one or more stacks to generate more electricity. End plate of PEMFC holds together all parts of it. Therefore, the material selection for end plate is important to provide safe conditions. To use PEMFC safely, investigation of material fracture energy is required to decide that the material is in safe conditions or not. There are three fracture energy modes which are mode I, mode II and mode III. There are many methods to investigate failure of material at different modes. Unlike other methods, Arcan specimen gives facility to evaluate of mode I, mode II and mixed modes. The main purpose of this paper was to compare the results of fracture energy (stain energy release rate) of different materials for end plates in fuel cells. Another goal was to select a sutitable material was selected as PEMFC end plate.

Vehicular application of Proton Exchange Membrane Fuel Cells (PEMFC) poses durability and stability issues toward the multiple start-stops operation. Start-stop cycle leads to performance decay for PEMFC over time. Considering its reliability, PEMFC's performance recovery becomes a major concern. In electrical vehicle which does not used hydrogen tank due to safety, PEMFC require fuel processor to produce hydrogen as fuel source from ethanol. Output temperature of hydrogen from fuel processor is about 80 °C, which is quite high for PEMFC. Temperature is alleged having an impact on the performance of PEMFC. This research is focused on studying the effect of start-stop cycle and hydrogen temperature on the performance of PEMFC under constant loads using electrochemical characterisation. The number of start-stop cycle was varied by 10, 20 and 30 cycles under constant loads of 1 and 0.5 ampere. The temperature that used for hydrogen was 40° C. The result shows that heating hydrogen to 40 °C does not have significant effect to PEMFC's performance. However, enhancing start-stop cycle number has increased degradation of PEMFC stack.

Heat and mass transfer performance of proton exchange membrane fuel cells with electrode of anisotropic thermal conductivity

Due to its chemical stability in acidic environments and high ionic conductivity, Nafion has proven to be an essential material in proton exchange membrane fuel cell (PEMFC) designs. Nafion functions as both a membrane – separating the two electrodes – and as a conductive binder in each catalyst layer (CL). Nano-thin films of Nafion ionomer allow protons to reach carbon-supported Pt catalysts. In addition to protons, oxygen and water also move through the nano-thin Nafion ionomer to and from reactive Pt sites. These physical transport processes directly impact PEMFC performance. Therefore, measuring and determining ways to improve upon each of these processes is critical in the development of high performance PEMFCs.In regards to thick Nafion membranes, conductivity and diffusion measurements can be readily performed in most laboratories. Nano-thin Nafion films on the other hand prove more challenging to study due to experimental limitations. Nevertheless, neutron reflectometry (NR) has been reported in literature as a capable technique to provide simultaneous quantitative structural and composition profiles for thin-film Nafion [1-5]. Results for Nafion at native silicon oxide interfaces show complex multi-layered structures forming distinct water-rich and water-poor regions [1-3]. Despite these advancements in our understanding of thin-film Nafion, it is still unclear how these observed structures may impact PEMFC performance. This is because silicon does not interface with Nafion in PEMFC CLs. Instead, carbon and Pt are the primary and secondary materials that interface with the thin-film ionomer. In the latter case, thin-film Nafion at Pt interfaces has been briefly studied in literature and shows significantly less structure than Nafion at silicon oxide interfaces [4,5]. Beyond the limited number of studies for Pt-Nafion interfaces, carbon-Nafion interface studies are even more scarce in literature [5]. This is likely because carbon black (i.e. the electron conductor in PEMFC CLs) is too rough to be used with NR. Therefore, to confidently assume the structure of Nafion at carbon black interfaces, trends from NR work on other carbon-based samples need to be compiled and compared, while considering their bonding structures and surface chemistries.In this work, we extend the understanding of thin-film Nafion at carbon interfaces by testing four different carbon-based substrates. Using thin-film Nafion (< 100 nm) deposited on each carbon sample, NR was performed in both dry and humidified environments. Fitting the data to these experiments, results suggest a variety of polymer structures at the carbon-Nafion interface. These include complex multi-layered structures, similar to those at silicon oxide interfaces, as well as simple homogenous films with little-to-no interfacial structure. During this presentation, the implications of these results on species transport in PEMFC CLs will be discussed. Additionally, PEMFC performance predictions that incorporate learnings from this study will be made using an extended model from our earlier work [6].[1] S.C. DeCaluwe, A.M. Baker, P. Bhargava, J.E. Fischer, and J.A. Dura, “Structure-property Relationships at Nafion Thin-film Interfaces: Thickness Effects on Hydration and Anisotropic Ion Transport,” Nano Energy, vol. 46, pp. 91–100, 2018.[2] J.A. Dura, V.S. Murthi, M. Hartman, S.K. Satija, and C.F. Majkrzak, “Multilamellar Interface Structures in Nafion,” Macromolecules, vol. 42, no. 13, pp. 4769–4774, 2009.[3] U.N. Shrivastava, H. Fritzsche, and K. Karan, “Interfacial and Bulk Water in Ultrathin Films of Nafion, 3M PFSA, and 3M PFIA Ionomers on a Polycrystalline Platinum Surface,” Macromolecules, vol. 51, no. 23, pp. 9839–9849, 2018.[4] V.S. Murthi, J. Dura, S. Satija, and C. Majkrzak, “Water Uptake and Interfacial Structural Changes of Thin Film Nafion Membranes Measured by Neutron Reflectometry for PEM Fuel Cells,” ECS Transactions, vol. 16, no. 2, 2019.[5] D.L. Wood, J. Chlistunoff, J. Majewski, and R.L. Borup, “Nafion Structural Phenomena at Platinum and Carbon Interfaces,” Journal of the American Chemical Society, vol. 131, no. 50, pp. 18096–18104, 2009.[6] C.R. Randall and S.C. DeCaluwe, “Physically Based Modeling of PEMFC Cathode Catalyst Layers: Effective Microstructure and Ionomer Structure–Property Relationship Impacts,” Journal of Electrochemical Energy Conversion and Storage, vol. 17, no. 4, Jan. 2020.

Proton-Exchange Membrane (PEM) Fuel Cells have the potential to contribute to the future of emission-free, efficient power systems for a wide range of applications. However, operational lifetime of the fuel cells is limited due to failure of cell components, with the membrane being one of the key ones. In PEFCs, chemical decomposition of the membrane due to the attacks of radicals formed during operation along with formation of pinholes, cracks, and delamination influenced by mechanical stressors leads to increased crossover of reactant gases and reduced power loss. Since the chemical and mechanical stressors are largely influenced by the temperature and humidity, it is difficult to determine what mechanisms dominate the membrane lifetime in operation. To understand underlying mechanisms of failure under chemical, mechanical, and combined chemical-mechanical degradation modes, and assess membrane lifetime in shorter time periods, accelerated stress testing (AST) methods are commonly employed. Swelling (or hydration) of the membrane is a key property in fuel cells since it controls both conductivity and stability of the membrane, which could be related to the cell performance and durability, respectively. Swelling-induced operational stresses in the membrane trigger failure mechanisms in the form of cracks or delamination, the impact of which could be further accelerated in the presence of chemical degradation.In this talk, the mechanical aspects of the durability of the polymer fuel cell membranes will be discussed at multiple length-scales. First, membrane's mechanical response during cell operation will be discussed along with the effects of swelling and mechanical properties. We will elaborate on how membrane deformation could be related to the mechanical failure modes ranging from fatigue behavior to the growth of pinholes and cracks, depending on the operating conditions and stress-states. Strategies that could potentially improve membrane durability by tuning its properties will also be discussed. The results will be demonstrated using experimental data as well as modeling methodologies.We will then show how the swelling and properties of membranes change with degradation by focusing on perfluorosulfonic-acid (PFSA) ionomers, the most widely studied membrane in PEM fuel cells. Changes in structure-property relationship of PFSA membranes due to degradation are highlighted based on the investigations on the morphology, mechanical properties and water uptake of degraded membranes. By studying the correlations between measured properties and structural features one can better understand the mechanical aspects of degradation. We will also elaborate how chemical and mechanical stressors could influence each other and control the overall membrane failure. Lastly, mechanistic approaches will be introduced to identify key membrane properties for mechanical durability, to simulate membrane deformation and failure, and to explore models for lifetime prediction. Acknowledgements The authors would like to thank the Los Alamos Fuel Cell Team for their help preparing the degraded membrane samples and for helpful discussions. This work was funded by the Assistant Secretary for Energy Efficiency and Renewable Energy, Fuel Cell Technologies Office, of the U.S. Department of Energy under contract number DE-AC02-05CH11231.

The polymer electrolyte membrane (PEM) fuel cell is a promising alternative power source for electric vehicles, forklifts, and stationary backup power due to its high power density, low operating temperature, and clean emissions. The gas diffusion layer (GDL) facilitates the transport of heat, reactant gases, water vapor, and liquid water in the PEM fuel cell. The GDL is a highly porous material composed of dense arrays of carbon fibers, resins, and polytetrafluoroethylene (PTFE). Additionally, it is typically coated with a micro porous layer (MPL), which results in the reduction of contact resistance at the catalyst layer interface and the overall improvement in water management. Effective water management must be achieved within the GDL over the entire operating lifetime in order to improve the commercial success of PEM fuel cells. Investigations into the effects of ageing on water management within the GDLs can be useful tools to guide this success. Water is required to maintain polymer electrolyte membrane hydration and ionic conductivity; however, excess water tends to accumulate in the catalyst layer, GDL, and flow channels. This accumulation limits mass transport and leads to performance losses. Therefore, effective water management in the GDLs is essential for improving cell performance, durability, and stability. Most GDL research has been focused on the impact of GDL materials and microstructure design on overall performance, rather than durability. Decreased GDL hydrophobicity has been found after only a few hundred hours of operation (1, 2). Therefore, a clear understanding of the influence of GDL degradation on the liquid water behavior is essential. As a tool to visualize this behaviour, synchrotron X-ray radiography is a powerful technique for visualizing liquid water transport behavior within an operating PEM fuel cell. High intensity X-rays generated at the BMIT-BM beamline of the Canadian Light Source were used for identifying liquid water inside the GDLs and capturing the multiphase flow behavior in an operating PEM fuel cell. Figure 1 is an example synchrotron X-ray radiograph of the fuel cell in operando, illustrating the spatial distribution of liquid water. The observed pixel brightness was correlated to the presence of liquid water, and the saturation profile across the GDL thickness was obtained. In this study, as-received fresh GDLs were immersed in a 35wt % solution of H2O2 at 90o C for 12 hours in order to perform an accelerated artificial ageing process. As-received fresh and artificially aged GDLs were then used to assemble specialized fuel cells for synchrotron imaging. Both the electrochemical performance and liquid water transport behavior were observed for a range of current densities. Additionally, the effect of changes in relative humidity on performance was compared to investigate the effect of artificial ageing. Notable differences in cell performance and liquid water transport behavior were observed at steady state operating conditions. The cell with aged GDLs showed lower cell voltage and higher quantities of liquid water than those of as-received fresh GDLs. The impacts of aging on the liquid water distributions within the GDL and on cell performance will be presented in this work. The objective of current work is to highlight the potential degrading effect on liquid water management in long term fuel cell operation.

The development of reliable power sources is important for the continuous operation of various electric equipment in unmanned aircraft and the field environment. Currently electric power delivery to such systems is mainly by battery packs. An alternative is to use fuel cells (FCs). FCs are electrochemical devices that are used to convert chemical energy of fuels such as hydrogen and methanol to electricity. Methanol is an attractive fuel because it is liquid at ambient temperature, has a much higher energy density than hydrogen and low reforming temperature (220–300 °C). Thus, integration of methanol steam reformers (MSRs) with FCs makes it possible to continuously produce electricity. The key challenge in such power system is the development of fuel cells which can be effectively operated at compatible temperature range of MSR, i.e., 220–300 °C in order to increase synergetic heat integration and system reliability. Herein, the latest development of high temperature polymer electrolyte membrane fuel cells (HT‐PEMFCs) is critically reviewed. The prospect of the integrated HT‐PEMFCs‐MSR as a reliable and compact power source is discussed. The results indicate that phosphoric acid doped polybenzimidazole (PA/PBI) membranes with in situ formed phosphosilicate nanocluster proton carriers show the technical feasibility of the development of HT‐PEMFCs at temperatures of 200–300 °C.