Tungsten oxide-based Z-scheme for visible light-driven hydrogen production from water splitting

The stoichiometric water splitting using a solar-driven Z-scheme approach is an emerging field of interest to address the increasing renewable energy demand and environmental concerns. So far, the reported Z-scheme must comprise two populations of photocatalysts. In the present work, only tungsten oxides are used to construct a robust Z-scheme system for complete visible-driven water splitting in both neutral and alkaline solutions, where sodium tungsten oxide bronze (Na0.56WO3–x) is used as a H2 evolution photocatalyst and two-dimensional (2D) tungsten trioxide (WO3) nanosheets as an O2 evolution photocatalyst. This system efficiently produces H2 (14 μmol h–1) and O2 (6.9 μmol h–1) at an ideal molar ratio of 2:1 in an aqueous solution driven by light, resulting in a remarkably high apparent quantum yield of 6.06% at 420 nm under neutral conditions. This exceptional selective H2 and O2 production is due to the preferential adsorption of iodide (I–) on Na0.56WO3–x and iodate (IO3–) on WO3, which is evidenced by both experiments and density functional theory calculation. The present liquid Z-scheme in the presence of efficient shuttle molecules promises a separated H2 and O2 evolution by applying a dual-bed particle suspension system, thus a safe photochemical process.