Simultaneous promotion of photocatalytic CH₄ conversion and H₂O₂ production via nanopore water confinement

Aqueous photocatalytic CH₄ oxidation offers a promising route for converting natural gas into oxygenates, a process governed by multi-electron and proton transfer at the catalyst-water interface. Here, we demonstrate that spatially confining water within Au/TiO₂@pSiO₂ core-shell catalysts-by reducing silica pore size to 1.7 nm-increases CH₄ conversion three-fold and H₂O₂ production 22-fold compared to Au/TiO₂. This strategy is generalizable to other semiconductors and cocatalysts, with Pt/TiO₂@pSiO₂-1.7 exhibiting oxygenate yields of 32.7 mmol g^-1 h^-1 and a 14.1% apparent quantum yield at 365 nm. Spectroscopic studies and molecular dynamics simulations reveal that water confined within pores, with a weakened hydrogen-bonding network, alters proton-coupled electron transfer pathways. Water oxidation transits to a concerted pathway, favoring •OH production for CH₄ conversion, while oxygen reduction shifts to a two-electron process, directly producing H₂O₂. This work highlights the potential of water confinement for designing efficient photocatalysts for CH₄ conversion.