(Invited) Solar-Driven H2O2 Production via Cooperative Auto- and Photocatalytic Oxidation in Fine-Tuned Reaction Media

Abstract

The industrial synthesis of H2O2 is based on the anthraquinone auto-oxidation process, which requires high-energy consumption and an expensive metal catalyst. Solar photocatalysis has been suggested as a green and sustainable process to produce H2O2. Although there have been significant advances in material design to improve the H2O2 production efficiency, the photocatalytic H2O2 production performance remains insufficient to meet industrial demands. In this study, we designed a new reaction environment using aryl alcohol as an organic photo-oxidation substrate. With a metal-free covalent triazine framework (CTF) as a model photocatalyst, we combined photo-oxidation with O2 reduction in fully organic conditions for the co-production of H2O2 and aryl aldehyde. Furthermore, such an organic system allows for the light-activated autocatalytic oxidation of aryl alcohol, facilitating O2 reduction kinetics by photo-initiated radicals. Inspired by an organic working solution of the anthraquinone process, we fine-tuned the reaction composition by varying the water-aryl alcohol-solvent ratios to improve the photocatalytic pathway, achieving one of the highest solar-to-chemical conversion efficiencies ever reported. The electrochemical assessment of the photocatalyst elucidates that the effect of water addition in the organic solution promotes the proton transfer from aryl alcohol to dissolved O2 molecules, boosting the H2O2 generation. This study demonstrates that tailoring the reaction media is a simple but effective route for promoting overall solar H2O2 productivity, providing a new opportunity in photocatalytic reactions.