Defected ZnWO₄-decorated WO₃ nanorod arrays for efficient photoelectrochemical water splitting

The utilization of solar energy in photoelectrochemical water splitting is a popular approach to store solar energy and minimize the dependence on fossil fuels. Herein, defected ZnWO₄-decorated WO₃ nanorod arrays with type II heterojunction structures were synthesized via a two-step solvothermal method. By controlling the amount of Zn precursor, WO₃ nanorods were decorated in situ with tunable amounts of ZnWO₄ nanoparticles. Characterization confirmed the presence of abundant W⁵⁺ species in the defected ZnWO₄-decorated WO₃ samples, leading to enhanced light absorption and charge-separation efficiency. Therefore, the decorated WO₃ nanorod arrays show much higher photoelectrochemical (PEC) activity than pure WO₃ nanorod arrays. Specifically, the sample with optimal ZnWO₄ decoration and surface defects exhibits a current density of 1.87 mA cm^-2 in water splitting at 1.23 V vs. RHE under 1 sun irradiation (almost 2.36 times higher than that of pure WO₃), a high incident photon-to-current efficiency of nearly 40% at 350 nm, and a relatively high photostability. However, the decoration of WO₃ with too much ZnWO₄ blocks the light absorption of WO₃, inhibiting the PEC performance, even when many defects are present. This work provides a promising approach to rationally construct defected heterojunctions as highly active PEC anodes for practical applications.