This paper will present the characterization of two types of membrane‐electrode‐assemblies (MEAs) for high‐temperature polymer electrolyte membrane fuel cells (HT‐PEMFC) working under reformate stream. The important aspects to be considered in the characterization of these MEAs are: (i) presence of contaminants, and (ii) composition of the anode. Start/stop cycling test were performed for two different Dapozol® MEAs using different GDL materials, using first hydrogen and then synthetic reformate as a fuel gas, both with a dew point of 80 °C. With these results the influence of contaminants present in the reformate was compared for the two types of MEAs, showing the superior performance of the Dapozol® 101 MEA under these conditions. The possibility to further enhance the MEAs' resilience against the operation of reformates by changing the anode catalyst composition was evaluated in a half MEA configuration, considering that the impact of the H2S present in the fuel presents a major issue. For this reason the hydrogen oxidation reaction (HOR) was evaluated for two types of Pt‐based electrocatalysts in an anodic half MEA configuration using different hydrogen‐rich fuel mixtures. These results provide valuable information for the optimization of the MEA and the anode catalyst for HT‐PEMFC.
12-Silicotungstic acid, a heteropoly acid (HPA) -was incorporated into phosphoric acid (PA) doped polybenzimidazole (PBI) membrane that exhibited strong mechanical stability, excellent proton conductivity, and can be used for high temperature proton exchange membrane fuel cells (PEMFCs). At 160 • C, an electrochemical impedance spectroscopy (EIS) fitting of the fuel cells data showed the membrane electrode assemblies (MEAs) made of PBI/20%HPA/PA had three times lower ohmic resistance (0.057 ± 0.002 Ohm * cm 2 ) as compared to the control reference of PBI/PA (0.160 Ohm * cm 2 ). In addition, the ohmic resistance of the composite MEA remained unchanged while the charge transfer resistance decreased after 313 hours conditioning. Fourier transform infrared spectroscopy (FTIR), magic angle spinning -nuclear magnetic resonance (MAS-NMR), and thermogravimetric analysis (TGA) showed 12-silicotungstic acid inhibits water from escaping the membrane at elevated temperatures and adds more acid sites, providing additional paths for proton transport. Scanning electron microscope (SEM), transmission electron microscopy (TEM), and small angle X-ray scattering (SAXS) were used to confirm the structure and morphology of PBI/20%HPA/PA membrane prior making the MEAs. Fuel cell technologies have the potential to reduce our dependence on fossil fuels and to reduce associated emissions of pollutants as the global population continues to grow. Polymer electrolyte membrane fuel cells (PEMFCs) have the advantage of being fully scalable for stationary power generation than other types of fuel cells. PEMFCs have outstanding power density, rapid start-up, and high efficiency. 1In addition, the operation of PEMFCs is straightforward and does not generate any additional pollutants. Despite several advantages, current PEMFCs are not yet widely used or commercialized, because they remain too expensive, do not have enough durability, and require very pure hydrogen as a fuel.2 At the moment, PEMFCs generally operate below 100• C due to the need to fully humidify commonly used perfluorosulfonic acid electrolytes such as Nafion. At low operating temperatures, a small concentration of CO or SO 2 impurities in the fuel could poison the catalysts and lower the fuel cell performance. Therefore, current PEMFCs require high purity hydrogen that can only be cost-effectively produced from natural gas at this time. Furthermore, the humidification of fuel and oxidant in low temperature PEMFCs requires a complicated humidification system. These technical challenges can be addressed by increasing operating temperatures above 120• C. High temperature operation is a promising way to improve PEMFC performance; it has been shown that higher operating temperatures would increase chemical kinetics at the anode and dramatically enhance the electrode tolerance to fuel impurities, which allows for the use of lower-cost hydrogen.3 In addition, fuel cell operation above 120• C can tolerate up to 1% CO and 10 ppm SO 2 . Operating at elevated temperatures would also provid...
The increasing requirement for renewable energy places high-temperature proton exchange membrane fuel cells (HT-PEMFCs) on the forefront of “green” energy-generating power devices. Compared to certain PEMFC technologies, HT-PEMFCs possess faster electrode kinetics, high tolerance to fuel poisons and impurities, no humidification requirements, simplified cooling and system design.1 Herein we present optimization strategies of membrane electrode assemblies (MEAs) for HT-PEMFCs, focusing mainly on the (1) component characterization, (2) MEA fabrication, and (3) testing protocols. A selection of gas diffusion electrodes (GDEs) was tested, as well as the presence/absence of a microporous layer (MPL) on the cell performance. The catalyst layer (CL) has been modified in the terms of fabrication methods, catalyst type, platinum (Pt) content, as well as a variety of binders and additives. The PEM optimizations focused on varying and testing: (1) the molecular weight (Mw) of polybenzimidazole (PBI) for membrane casting, (2) PEM thickness, and its (3) acid doping levels (ADL). The MEAs were then fabricated at altering hot-pressing conditions and their performances were compared. The MEA testing focused on activation, humidity levels, high current operations, elevated temperature and pressure operations, as well as long-term stationary and dynamic durability protocol studies. The material fabrication optimizations resulted in higher onset and peak-of-life voltages, as well as longer cell durability. Together with optimized cell testing, we have achieved power densities of more than 0.8 W/cm2, with stationary durability of more than 13,000 hours at 0.3 A/cm2 current density, with the degradation rate of 4 μV/h. Originally the dynamic durability was demonstrated with more than 290 start-stop cycles showing the performance degradation of up to 100 µV/cycle, however, new tests show degradation rates of less than 46 µV/cycle. The performance and durability that we have demonstrated here position HT-PEMFCs as matured technology that can enter the mass market as a commercial and reliable electrochemical power device, to answer the ever-increasing societal energy demands in the age of climate change. Figure 1. Performance of Blue World Technologies MEAs: (A) from different production batches showing small performance scatter, and (B) i-V and power curves at elevated pressures. Reference: 1. O. Jensen, D. Aili, H. A. Hjuler, Q. Li, High Temperature Polymer Electrolyte Membrane Fuel Cells - Approaches, Status and Perspective, ISBN 978-3-319-17081-7; DOI 10.1007/978-3-319-17082-4, Springer International Publishing, New York, 2015. Figure 1
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