High-Performance PEMFCs at Elevated Temperatures Using Nafion 112 Membranes

Operating proton exchange membrane fuel cells (PEMFCs) at elevated temperatures (>100°C) reduces the effect of CO poisoning, simplifies heat rejection, and results in more useful waste heat. Membrane electrode assemblies were developed to obtain high-performance PEMFCs at elevated temperatures and low relative humidity (RH) using the commercial Nafion 112 membrane. Cell polarization was obtained at three operating conditions (cell temperature °C/anode %RH/cathode %RH) of 80/100/75, 100/70/70, and 120/35/35, ambient pressure. Hydrogen/air cell performance at 400 mA/cm 2 was 0.72, 0.69, and 0.58 V at the three conditions, respectively. A cell voltage of 0.65 V was obtained at the 120°C condition when oxygen was used instead of air. Reproducible cell performance with the maximum voltage difference of 10 mV was obtained at all operating conditions. The hydrogen crossover rate through the Nafion 112 membrane was relatively low, between 0.6 and 1.3 mA/cm 2 at temperatures between 25 and 120°C. The electrochemical surface area of each cathode electrode, determined from cyclic voltammetry, was 97 m 2 /g Pt, with nearly 73% catalyst utilization. The performance optimization approach can be applied to more advanced high-temperature membranes that have higher conductivity at low RH when these membranes are available in the future.

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