Tommy T.H. Cheng

Relative Humidity Effect on Anode Durability in PEMFC Startup/Shutdown Processes

Ru dissolution and crossover to the cathode from PtRu anode catalysts, which are commonly used in polymer electrolyte membrane fuel cells (PEMFCs) to provide CO tolerance for reformate-based fuel cell applications, have been previously identified as critical durability issues. In this investigation, the effect of relative humidity (RH) on Ru dissolution and crossover was studied using an anode accelerated stress test (AST) to mimic anode potential variation that occur during fuel cell start-ups and shut-downs. Stress testing at lower RH resulted in less Ru degradation, which was indicated by changes in cyclic voltammetry (CV), namely CO stripping peak shifts. The relative degree of Ru crossover was also reflected by the decreases in cell performance and CO tolerance. The results highlight the critical role of water in the Ru degradation mechanism and indicate that controlling the RH could be an effective strategy to mitigate Ru crossover.

PEMFC MEA and System Design Considerations

Proton exchange membrane fuel cells (PEMFCs) are being developed and sold commercially for multiple near term markets. Ballard Power Systems is focused on the near term markets of backup power, distributed generation, materials handling, and buses. Significant advances have been made in cost and durability of fuel cell products. Improved tolerance to a wide range of system operation and environmental noises will enable increased viability across a broad range of applications. In order to apply the most effective membrane electrode assembly (MEA) design for each market, the system requirements and associated MEA failures must be well understood. The failure modes associated with the electrodes and membrane degradation are discussed with respect to associated system operation and mitigating approaches. A few key system considerations that influence MEA design include expected fuel quality, balance-of-plant materials, time under idle or open circuit operation, and start-up and shut-down conditions.