Enhanced solar water oxidation by CoWO4-WO3 heterojunction photoanode

Abstract

Tungsten oxide (WO3) is a low band-gap semiconductor with valence band maximum favorably located for photo-electrochemical water oxidation under sunlight but its performance suffers from fast recombination of photo-generated electrons and holes. In order to suppress recombination and reduce photocorrosion, herein, we report the fabrication of a facile heterojunction photoanode design by combining n-type WO3 nanoplates with p-type cobalt tungstate (CoWO4) nanocuboids produced by simple chemical precipitation methods followed by their successive deposition on a FTO glass substrate. The hybrid photoanode not only exhibited a reduction of the onset potential but also demonstrated up to 2.4 times increase in the photocurrent density compared to those with the bare WO3 electrode when tested for photo-electrochemical (PEC) water oxidation using techniques such as linear sweep voltammetry, transient photo amperometry, electrochemical impedance spectroscopy under 1.5 AM G simulated solar light. The band aligned hybrid design of the photoanode helped to suppress the recombination of electrons and holes before utilization in water oxidation. In addition, the use of back illumination ensured the avoidance of light shading of primary photo absorber (WO3) by the co-catalyst (CoWO4) as well as reduced photocorrosion of WO 3by electrolyte leading to enhanced and stabilized photocurrent. Thus, the CoWO4 -WO3 based novel photoanode developed in this work shows good promise as a facile, low-cost and durable photoanode for PEC water oxidation, especially at low bias as confirmed by the two-terminal measurements.