Hydrogen crossover raises serious concerns on proton exchange membrane water electrolyzer

Green hydrogen plays a crucial role in the modern energy system, especially considering its production with the input of renewable electricity. Proton exchange membrane water electrolysis is favored for producing green hydrogen with renewable electricity, because of its high efficiency, rapid start-up, and quick adaptation to electricity changes. However, the hydrogen crossover issue gradually attracts significant attention under variable electricity input. The hydrogen crossover mechanism is proposed, with emphasis on its aggravation during the frequent start-stop cycles. The preliminary experimental observations and theoretical insights are reported to assess the hydrogen crossover rate under constant and dynamic operating conditions. Dynamic operation can particularly intensify the hydrogen permeation, increasing anode-side hydrogen volume fraction in oxygen and membrane degradation, thereby aggravating the safety risk and reducing efficiency. Several possible mitigation strategies, such as catalytic layer design, membrane material optimization, and operational condition control, are proposed.