Photoactive Tungsten-Oxide Nanomaterials for Water-Splitting.

This review focuses on tungsten oxide (WO) and its nanocomposites as photoactive nanomaterials for photoelectrochemical cell (PEC) applications since it possesses exceptional properties such as photostability, high electron mobility (12 cm V s) and a long hole-diffusion length (150 nm). Although WO has demonstrated oxygen-evolution capability in PEC, further increase of its PEC efficiency is limited by high recombination rate of photogenerated electron/hole carriers and slow charge transfer at the liquid-solid interface. To further increase the PEC efficiency of the WO photocatalyst, designing WO nanocomposites via surface-interface engineering and doping would be a great strategy to enhance the PEC performance via improving charge separation. This review starts with the basic principle of water-splitting and physical chemistry properties of WO, that extends to various strategies to produce binary/ternary nanocomposites for PEC, particulate photocatalysts, Z-schemes and tandem-cell applications. The effect of PEC crystalline structure and nanomorphologies on efficiency are included. For both binary and ternary WO nanocomposite systems, the PEC performance under different conditions-including synthesis approaches, various electrolytes, morphologies and applied bias-are summarized. At the end of the review, a conclusion and outlook section concluded the WO photocatalyst-based system with an overview of WO and their nanocomposites for photocatalytic applications and provided the readers with potential research directions.