High-pressure water electrolysis: Electrochemical mitigation of product gas crossover

• New technique to reduce gas crossover during water electrolysis
• Increase of the efficiency of pressurized water electrolysis
• Prevention of safety hazards due to explosive gas mixtures caused by crossover
• Experimental realization for a polymer electrolyte membrane electrolyzer
• Discussion of electrochemical crossover mitigation for alkaline water electrolysis

Hydrogen produced by water electrolysis can be used as an energy carrier storing electricity generated from renewables. During water electrolysis hydrogen can be evolved under pressure at isothermal conditions, enabling highly efficient compression. However, the permeation of hydrogen through the electrolyte increases with operating pressure and leads to efficiency loss and safety hazards. In this study, we report on an innovative concept, where the hydrogen crossover is electrochemically mitigated by an additional electrode between the anode and the cathode of the electrolysis cell. Experimentally, the technique was applied to a proton exchange membrane water electrolyzer operated at a hydrogen pressure that was fifty times larger than the oxygen pressure. Therewith, the hydrogen crossover was reduced and the current efficiency during partial load operation was increased. The concept is also discussed for water electrolysis that is operated at balanced pressures, where the crossover of hydrogen and oxygen is mitigated using two additional electrodes.