Oscillation mechanism in polymer electrolyte membrane fuel cell studied by <i>operando</i> monitoring of oxygen partial pressure using optical probes

The stability of polymer electrolyte fuel cells（PEFCs）during power generation is one the most important issues, especially at high current densities. A new oscillation phenomenon was observed in a PEFC with 10-straight channels operated temperature 60 ℃ and relative humidity 60% using gas diffusion layer（GDL）without micro porous layer cathode. cell voltage oscillated periodically under constant-current operation. period amplitude were approximately 2 s 20 mV, respectively, but changed different flow rates An operando system developed for detecting oxygen partial pressure（p（O2））using optical probes. p（O2）during synchronized voltage. During oscillation, generated water proposed to increase accumulate catalyst layer（CL）, accordingly lowering transport thus reduction reaction oxygen. larger overvoltage resulted heat CL, by which liquid having accumulated CL removed as vapor GDL. This could be more pronounced higher density.