Electrocatalytic synthesis of pure H2O2 from crossover oxygen through a porous proton exchange membrane

Hydrogen peroxide (H₂O₂) is a valuable chemical, and its eco-friendly electrochemical production has gained attention to obtain pH-neutral aqueous solutions without impurities. However, achieving H₂O₂ faradaic efficiencies (FEs) above 30 % has been a challenge with conventional proton exchange membrane (PEM) electrolyzers. To enhance H₂O₂ FE, efficient collection of H₂O₂ from the catalyst surface using liquid water is necessary, but oxygen diffusion becomes a limiting factor in aqueous-immersed systems. To overcome this, we designed a zero-gap electrolyzer, supplying oxygen gas from the anode side through the membrane to the cathode. A gas flow-through porous PEM was developed by embedding an acidic ionomer into a membrane filter, enabling the crossover oxygen supply to the cathode flooded with water. This porous PEM design facilitated the formation of a three-phase interface at the catalyst, where high-concentration oxygen gas and liquid water interact closely, achieving 79 % H₂O₂ FE at 5 mA cm⁻². Continuous synthesis of pure H₂O₂ solution exceeding 5500 mg L⁻¹ (0.55 wt%) was sustained for over 50 hours.