Inter-Ring Bonding Electron Donor Structure Triggers Efficient Two-Electron Water Oxidation for Photocatalytic...

Low water oxidation efficiency is a major barrier to efficient photocatalytic hydrogen peroxide (H₂O₂) synthesis under sacrificial agent-free conditions. Among various water oxidation pathways, the two-electron water oxidation reaction (2e^- WOR) is promising due to its direct H₂O₂ generation and kinetic advantages. However, effective strategies to trigger the efficient 2e^- WOR remain insufficient. In this study, conjugated polymers with alternating electron donor and acceptor units are designed and synthesized. By introducing an inter-ring bonding electron donor structure with two linked phenyl rings, the efficient 2e^- WOR is initiated, increasing H₂O₂ synthesis efficiency from 1657 to 4401 µmol g^-1 h^-1 and achieving a solar-to-chemical conversion (SCC) efficiency of 1.25%. In-depth studies reveal that the 2e^- WOR is initiated by the inter-ring bonding electron donor structure, which enhances electron delocalization in the highest occupied molecular orbital (HOMO), increasing the valence band potential from 1.6 to 1.8 V, thereby meeting the oxidation potential required for the 2e^- WOR. Additionally, this structure promotes hole accumulation at low-energy barrier sites, boosting water oxidation efficiency from 874 to 2767 µmol g^-1 h^-1. This work presents a promising strategy for improving photocatalytic water oxidation efficiency, advancing sustainable H₂O₂ production.