BiVO<sub>4</sub> Film Coupling with CoAl<sub>2</sub>O<sub>4</sub> Nanoparticles for Photoelectrochemical Water Splitting\nUtilizing Broad Solar Spectrum through p–n Heterojunction,\nPhotothermal, and Cocatalytic Sy

Water\noxidation is an endothermic and kinetics–sluggish\nreaction; the research of photoanodes with photothermal and cocatalytic\nproperties is of great significance. Herein, BiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub> film photoanodes were studied for solar water\nsplitting through coupling spinel p-type CoAl<sub>2</sub>O<sub>4</sub> nanoparticles on n-type BiVO<sub>4</sub> films. Compared to the\nBiVO<sub>4</sub> photoanode, better performance was observed on the\nBiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub> photoanode during water\noxidation. A photocurrent of 3.47 mA/cm<sup>2</sup> was produced on\nthe BiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub> photoanode at 1.23\nV vs RHE, which is two-fold to the BiVO<sub>4</sub> photoanode (1.70\nmA/cm<sup>2</sup>). Additionally, the BiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub> photoanodes showed an acceptable stability for water\noxidation. The BiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub> photoanode\nbeing of higher water oxidation performance could be attributed to\nthe presence of p–n heterojunction, cocatalytic, and photothermal\neffects. In specific, under the excitation of λ < 520 nm\nlight, the holes produced in/on BiVO<sub>4</sub> can be transferred\nto CoAl<sub>2</sub>O<sub>4</sub> owing to the p–n heterojunctions\nof BiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub>. Meanwhile, the\ntemperature on the BiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub> photoanode\nrises quickly up to ∼53 °C under AM 1.5 G irradiation\ndue to the photothermal property of CoAl<sub>2</sub>O<sub>4</sub> through\ncapturing the 520 < λ < 720 nm light. The temperature\nrising on the BiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub> photoanode\nimproves the cocatalytic activity of CoAl<sub>2</sub>O<sub>4</sub> and modifies the wettability of BiVO<sub>4</sub>/CoAl<sub>2</sub>O<sub>4</sub> for effective water oxidation.