Hydrogen (H-2) cross-over through membrane electrolyte is a critical safety issue in proton exchange membrane (PEM) electrolysis. Permeated H-2 tends to be consumed by oxidation or recombination at the anode. In this study, the contribution of oxidation/recombination to the reduction of H-2 content in the anode compartment was quantitatively evaluated by measuring the H-2 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 H-2 flux through the membrane was consumed at the anode by oxidation or recombination when the cathode pressure was under 10 bars. Therefore, promoting H-2 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 H-2 content in the anode. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.