Boosting oxygen mass transfer for efficient H2O2 generation via 2e−-ORR: A state-of-the-art overview

Green H2O2 formation via electrochemical two-electron oxygen reduction reaction (2e--ORR) is a critical approach, which could substitute the industry-dominant anthraquinone one, especially for the decentralized demand. There are a series of outstanding and comprehensive reviews about the rational design of cathodes or catalysts with diverse active sites to improve the reactivity/selectivity of 2e--ORR. However, the mass transfer of oxygen is crucial in H2O2 formation via 2e--ORR, especially at high current densities, where the related reviews summarizing the state-of-art are limited. In this manner, we tend to summarize the recent developments to boost oxygen mass transfer based on the different oxygen supplies. It could divide into three categories: (ⅰ) submerged cathodes utilizing dissolved oxygen, (ⅱ) pressurized gas diffusion electrodes using pressured air/oxygen, and (ⅲ) gas diffusion electrodes with natural air in the absence of aeration. Finally, challenges are singled out, and prospects are described. This review aims to highlight the significance of oxygen mass transfer in 2e--ORR for H2O2 generation, eventually providing essential ideas for the smart design of highly effective systems for H2O2-based technologies.