Simultaneous Activation of the Surface and Interior of Mo3S9-Anchored Carbon Nitride to Boost Photocatalytic Overall Water Splitting.

Solar-driven photocatalytic overall water splitting (POWS) represents a highly promising route for sustainable energy production, but its efficiency is limited by rapid charge recombination and slow kinetics of the hydrogen evolution reaction (HER) and oxygen evolution reaction (OER). To address these issues, we designed a novel carbon nitride (CN) photocatalyst based on a volume photocatalysis (VPs) strategy that features spatially separated HER and OER sites. Specifically, Mo3S9 clusters anchored on the CN surface serve as HER cocatalysts, while the abundant interior carbon atoms of CN act as cocatalyst-free OER centers, which are activated via hydroxylation/depolymerization. A room-temperature LiOH treatment was developed to controllably induce CN hydroxylation and depolymerization. Surface hydroxylation promotes water dissociation, significantly enhancing HER kinetics on Mo3S9. Meanwhile, interior hydroxylation and depolymerization improve water dissociation and facilitate water diffusion within the interior/volume, jointly boosting the volume OER. Consequently, the optimized cocatalyst-engineered CN photocatalyst exhibits excellent POWS performance in pure water, achieving a nearly 2000-fold enhancement over pristine CN, with solar-to-hydrogen (STH) efficiencies of 1.21% at room temperature and 1.58% at 55°C. The apparent quantum yield (AQY) reaches 42.1% at 380 nm and 55°C. This work provides insights into designing and fabricating efficient, low-cost photocatalysts for POWS.