Promoting Proton Donation through Hydrogen Bond Breaking on Carbon Nitride for Enhanced H₂O₂ Photosynthesis

Photocatalytic H₂O₂ production has attracted much attention as an alternative way to the industrial anthraquinone oxidation process but is limited by the weak interaction between the catalysts and reactants as well as inefficient proton transfer. Herein, we report on a hydrogen-bond-broken strategy in carbon nitride for the enhancement of H₂O₂ photosynthesis without any sacrificial agent. The H₂O₂ photosynthesis is promoted by the hydrogen bond formation between the exposed N atoms on hydrogen-bond-broken carbon nitride and H₂O molecules, which enhances proton-coupled electron transfer and therefore the photocatalytic activity. The exposed N atoms serve as proton buffering sites for the proton transfer from H₂O molecules to carbon nitride. The H₂O₂ photosynthesis is also enhanced through the enhanced adsorption and reduction of O₂ gas toward H₂O₂ on hydrogen-bond-broken carbon nitride because of the formation of nitrogen vacancies (NVs) and cyano groups after the intralayer hydrogen bond breaking on carbon nitride. A high light-to-chemical conversion efficiency (LCCE) value of 3.85% is achieved. O₂ and H₂O molecules are found to undergo a one-step two-electron reduction pathway by photogenerated hot electrons and a four-electron oxidation process to produce O₂ gas, respectively. Density functional theory (DFT) calculations validate the O₂ adsorption and reaction pathways. This study elucidates the significance of the hydrogen bond formation between the catalyst and reactants, which greatly increases the proton tunneling dynamics.