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 CuWO4/BiVO4/FeCoO x film deposited entirely by RF-magnetron sputtering using homemade ceramic targets. Our CuWO4/BiVO4 photoanode exhibits a significant photocurrent density of 0.82 mA cm–2 at 1.23 V vs RHE under AM 1.5G illumination, which is a record 382% increase compared to that of the bare CuWO4 film. To further boost the PEC performance, we deposited an ultrathin layer of amorphous FeCoO x cocatalyst, resulting in a triple CuWO4/BiVO4/FeCoO x heterojunction with a significant reduction in onset potential and a 500% increase in the photocurrent density of bare CuWO4. 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 CuWO4/BiVO4 heterojunction, potentially limiting its application in tandem systems. Conversely, the deposition of the FeCoO x ultrathin layer over the CuWO4/BiVO4 heterojunction induces a p–n junction on the BiVO4/FeCoO x interface, which, when combined with the abundant FeCoO x 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.

BiVO4 is a well-known n-type semiconductor with great potential for photoelectrochemical (PEC) conversion of solar energy into chemical fuels. Nevertheless, photocurrent densities achieved for bare BiVO4 photoanodes are still far...

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