Impact of hydrogen bleeding into the cathode feed of a PEM fuel cell

Hydrogen bleeding into the cathode inlet of a proton exchange membrane (PEM) fuel cell could be a simple approach to reduce the H₂ concentration in the fuel cell exhaust during transient operating conditions (e.g., start-up or fast transients) of a PEM fuel cell system; it could also serve as an additional heating source during cold start-up. In this experimental study, we address the question whether the chemical stability of the polymer electrolyte membrane is affected negatively by a hydrogen bleed into the cathode inlet of a PEM fuel cell. First, rotating ring disc electrode (RRDE) experiments were carried out to detect whether any additional H₂O₂ is produced during the oxygen reduction reaction in O₂ saturated electrolytes in the absence and presence of H₂. Dry open circuit voltage (OCV) experiments were then performed for more than 250 hours in 50 cm² single cells at 120°C and 18% relative humidity (RH) in order to investigate the effect of a 4 vol. % H₂-bleed into the cathode inlet on membrane stability. Finally, the distribution of membrane pin-holes was determined on membrane electrode assemblies (MEAs) after the dry OCV tests conducted with or without H₂-bleed using an infrared (IR) camera setup. In addition, the diffusion-limited hydrogen oxidation current on the cathode side was modeled in order to estimate the maximum areal heat flux near the cathode inlet, which would be caused if the H₂ oxidation rate were to be diffusion-limited.