Effect of cathode ink formulation on the hydrogen crossover and cell performance of proton exchange membrane water electrolyzers

The permeation of H2 through the membranes of proton exchange membrane water electrolyzers (PEMWEs) is a critical safety concern because of the risk of explosion when H2 mixes with O2 at the anode and increases in concentration. In this study, we investigated the modification of the cathode catalyst layer in the membrane electrode assembly as a strategy for achieving the safe operation of PEMWEs. The effects of the polytetrafluoroethylene (PTFE) content and type of ionomer in the cathode catalyst layer on the dissolved H2 concentration, H2 crossover, and electrochemical performance were investigated. The lowest dissolved H2 concentration and H2 permeation rate were achieved when 8 wt% PTFE was used. Consequently, the H2 volume fraction in O2 at the anode was less than 0.88 %. Additionally, using the Nafion ionomer (D520, ion exchange capacity: 1 mmol g−1), H2 volume fractions of 1.27 % and 1.34 % were obtained at 0.08 and 5 A cm−2, respectively. These values are below the lower explosion limit of H2 in O2 (4 %), implying that the PEMWE can be safely operated in the low-to-high current density range under ambient pressure. These results provide key guidelines for the design of high-safety cathode catalyst layers for PEMWEs.