Ternary Oxide CuWO/BiVO/FeCoO Films for Photoelectrochemical Water Oxidation: Insights into the Electronic Structure and Interfacial Band Alignment.

Photoelectrochemical (PEC) water oxidation using ternary oxide systems has been considered a promising approach for investigating the effective utilization of sunlight and the production of green fuel. Herein, we report a ternary-oxide-based CuWO/BiVO/FeCoO film deposited entirely by RF-magnetron sputtering using homemade ceramic targets. Our CuWO/BiVO photoanode exhibits a significant photocurrent density of 0.82 mA cm at 1.23 V vs RHE under AM 1.5G illumination, which is a record 382% increase compared to that of the bare CuWO film. To further boost the PEC performance, we deposited an ultrathin layer of amorphous FeCoO cocatalyst, resulting in a triple CuWO/BiVO/FeCoO heterojunction with a significant reduction in onset potential and a 500% increase in the photocurrent density of bare CuWO. Experimental and theoretical approaches were used to provide insights into the interfacial band alignment and photoinduced charge carrier pathway across heterojunctions. Our results reveal noticeable interface potential barriers for charge carriers at the CuWO/BiVO heterojunction, potentially limiting its application in tandem systems. Conversely, the deposition of the FeCoO ultrathin layer over the CuWO/BiVO heterojunction induces a - junction on the BiVO/FeCoO interface, which, when combined with the abundant FeCoO oxygen vacancies, results in improved charge separation and transport as well as enhanced photoelectrochemical stability. Our study provides a feasible strategy for producing photocatalytic heterojunction systems and introduces simple tools for investigating interface effects on photoinduced charge carrier pathways for PEC water splitting.