Cross-permeation and consumption of hydrogen during proton exchange membrane electrolysis

Hydrogen (H2) cross-over through membrane electrolyte is a critical safety issue in proton exchange membrane (PEM) electrolysis. Permeated H2 tends to be consumed by oxidation or recombination at the anode. In this study, the contribution of oxidation/recombination to the reduction of H2 content in the anode compartment was quantitatively evaluated by measuring the H2 content during electrolysis operation of a unitized reversible fuel cell stack in which the anode catalyst layer (CL) contained platinum (Pt). The results of fitting calculation indicated that over 70% of permeated H2 flux through the membrane was consumed at the anode by oxidation or recombination when the cathode pressure was under 10 bars. Therefore, promoting H2 consumption due to the addition of Pt in either the CL and/or current collector is critical for safe PEM electrolysis. Furthermore, optimization of the electrode structure is also important not only to increase the Faraday (current) efficiency but also to reduce the H2 content in the anode.