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On the choice of applied potential in ex situ testing of bipolar plate materials

Electrochemical energy conversion devices, such as fuel cells and electrolyzers, are widely recognized as an essential component of the transition to a low carbon economy. Polymer electrolyte membrane (PEM) variants of both technologies show particular promise due to their high current density, fast start-up times and low gas crossover rates. The main barrier to widespread uptake of these devices is their capital cost, which includes both raw material and manufacturing costs.

Product Number: 51323-19547-SG
Author: Gareth Hinds
Publication Date: 2023
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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.

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.