An on-demand solar hydrogen-evolution system for unassisted high-efficiency pure-water splitting

Abstract

Solar water splitting of pure water offers an attractive means for sustainable and carbon-free H₂ production. However, current photocatalytic H₂ production systems still suffer from two basic issues: the kinetic bottleneck for O₂ release and the easy toxicity of the photocatalysts. Here, we developed a consolidated photocatalyst, namely g-C₃N_3.5(O_0.5H_0.5), that can boost sustainable and superior H₂ evolution without using any sacrificial reagent. By conceptual design analysis as the guideline for three synthetic steps, the surface hydroxylation structure of g-C₃N_3.5(O_0.5H_0.5) concurrently increases the toxicity resistance and maximizes the charge separation for H₂ evolution. The obtained surface-hydroxylated g-C₃N_3.5(O_0.5H_0.5) photocatalyst exhibited unassisted high-efficiency pure-water-splitting activity, with a benchmark H₂-evolution rate up to 947.7 μmol h⁻¹ g⁻¹ under visible-light irradiation. Notably, the quantum efficiency of the g-C₃N_3.5(O_0.5H_0.5) suspension reached ∼10.6 and ∼2.5% at 420 and 520 nm, respectively, 10–20 times that of pristine g-C₃N₄. For the first time, we observed a key phenomenon that H₂O molecules can rapidly capture the photoexcited holes to produce H₂O₂, which can greatly promote the efficient charge separation for high H₂ evolution.