Photocatalysis of water into hydrogen peroxide over an atomic Ga-N₅ site

Tuning photocatalytic selectivity towards industrially significant yet thermodynamically unfavourable products remains challenging. Here a Ga-N₅ atomic site on macroporous inverse-opal-type carbon nitride (CNIO-GaSA) is designed and synthesized for visible-light-driven direct photosynthesis of hydrogen peroxide from molecular oxygen and water. The conversion of oxygen and water into hydrogen peroxide was found to occur via a metastable two-electron water oxidation and two-electron oxygen reduction pathway. The CNIO-GaSA photocatalyst exhibits a high reactivity of 331.7 μmol g⁻¹ h⁻¹ for H₂O₂ production, with a solar-to-chemical conversion efficiency of 0.4%, which is much higher than that for natural photosynthesis in plants (∼0.1%). Additionally, CNIO-GaSA installed in a photocatalytic flow system device can kill bacteria with 100% efficiency and retain high stability, indicating this system could be suitable for purifying natural water. Combined experimental characterizations and density functional theory simulations reveal that the intermediate states consisting of hybridized Ga 4p and N 2p from the Ga-N₅ site can not only enhance the separation/transfer of charge carriers, but also promote the adsorption/activation of water and the formation of a *OH intermediate, which is the rate-determining step for two-electron water oxidation. [Figure not available: see fulltext.]