Recombination layers for effective hydrogen crossover mitigation in proton exchange membrane water electrolyzers: Fabrication, characterization, and fundamental principles of operation

One major challenge that proton exchange membrane water electrolyzers (PEMWEs) face is hydrogen (H2) gas crossover. If left unmitigated, H2 crossover impacts the cell durability and becomes a safety issue. Fabrication of a catalytic recombination layer (RL) within the volume of the proton exchange membrane that provides active catalytic sites for recombination of hydrogen and oxygen gas molecules to water, is a viable strategy for H2 crossover mitigation. This paper reports on designing, fabrication, and testing of membrane electrode assemblies (MEAs) for PEMWEs with two RLs. The recombination layers are incorporated into the volume of the membrane of a MEA fabricated by the reactive spray deposition technology (RSDT) method. As fabricated MEAs with an active area of 25 cm2 and low catalyst loadings (0.3 mgIr cm-2 on the anode and 0.2 mgPt cm-2 on the cathode) demonstrated excellent performance. The RSDT-fabricated RLs demonstrated effective reduction of the H2 crossover from about 50% of the lower flammability limit (LFL) to below 10% of the LFL, when operating at current densities between 0.58 A cm-2 and 1.86 A cm-2. Electrochemical impedance spectroscopy and distribution of relaxation times analysis are used to study the mechanism of the recombination reaction for both RLs. The analysis of the results provides for the first-time insights into the fundamental mechanism of the H2 and O2 recombination reaction on the Pt active catalytic sites in the RLs integrated in the membrane of PEMWEs.