Rational nanopositioning of homogeneous amorphous phase on crystalline tungsten oxide for boosting solar water oxidation

Surface defect engineering of metal oxide is a promising approach for efficient photoelectrochemical (PEC) water splitting. However, the role of an amorphous overlayer with disordered crystallinity is debated, as it can induce crucial charge traps and undesired charge recombination. Herein, we demonstrate a rationally designed nanopositioning of a homogenous amorphous phase on the surface of crystalline metal oxide via a facile surface defect engineering to strongly enhance photoelectrochemical (PEC) water oxidation. The nanopositioning of the localized amorphous phase generates crystalline–amorphous (CA) homogeneous boundaries on the crystalline metal oxide. The amorphous phase provides the increased active adsorption sites, while the exposed crystalline phase promotes the charge transport. The results of analysis conducted on the rationally designed model case of crystalline–amorphous tungsten oxide (CA-WO₃) photoanode confirm a 2.5-fold higher photocurrent density (3.34 mA cm⁻²) at 1.23 V versus reversible hydrogen electrode under 1 sun illumination compared with the bare crystalline WO₃ (1.35 mA cm⁻²). With the rationally designed surface defects, we achieve the high-efficiency charge separation and catalytic kinetics. This work provides guidance for the rational design of surface defects on crystalline metal oxides for boosting the PEC water splitting.