On the Choice of Applied Potential in Ex Situ Testing of Bipolar Plate Materials

Abstract Ex situ testing of candidate bipolar plate materials for polymer electrolyte membrane (PEM) fuel cells and electrolyzers typically involves electrochemical polarization of the specimen in a three electrode cell. Relatively high potentials of between 1.5 V and 2.0 V vs RHE are commonly applied during such tests due to the widely held assumption that, during both start-up/shutdown and normal operation, the bipolar plate experiences the same potential as that of the nearest electrode. Here we present experimental and modelling evidence that the bipolar plate in an operating PEM fuel cell or electrolyzer actually sits at its natural open circuit potential due to the high resistivity of the aqueous phase in such devices, which effectively shields the material from the elevated potential at the electrode. The implications for reliable ex situ testing are discussed.