The maximum potential a PEM fuel cell cathode experiences due to the formation of air/fuel boundary at the anode

In this short communication, a misconception about the maximum potential a polymer electrolyte membrane fuel cell (PEMFC) cathode experiences due to the formation of fuel/air boundary at the anode during startup/shutdown is clarified. It is shown, conceptually, that the maximum potential experienced by a cathode in PEMFC under such condition is about twice the potential observed when one connects a driving fuel cell to a driven cell (electrolyzer), both of which having the same physical characteristics and operating under the same conditions.