Photothermal effect and hole transport properties of polyaniline for enhanced photoelectrochemical water splitting of BiVO₄ photoanode

As modification strategies are actively developed, the photothermal effect is expected to be a viable way to enhance the PEC water splitting performance. Herein, we demonstrate that the photothermal polyaniline (PANI) layer inserted between CoF₂ cocatalyst and BiVO₄ can enhance the photocurrent density of pure BiVO₄ by 3.50 times. The coated PANI layer exhibits excellent photothermal conversion and hole transport properties. Under near-infrared (NIR) light irradiation at 808 nm, PANI can raise the temperature of the photoanode in situ, thus promoting bulk charge transfer and broadening the light absorption range. After the CoF₂ cocatalyst is deposited on the BiVO₄/PANI surface, the water oxidation activity of the composite photoanode is also significantly enhanced due to the temperature elevation. In addition, density-functional theory (DFT) simulations demonstrate that BiVO₄/PANI/CoF₂ can dramatically reduce the energy barrier required for oxygen evolution reaction, accelerating the oxygen evolution kinetics. Under NIR light irradiation, the meticulously designed BiVO₄/PANI/CoF₂ (BPC) photoanode displays a photocurrent density of 4.34 mA cm^-2 at 1.23 V vs. RHE (V_RHE) with an excellent charge injection efficiency of 88.14 %. In addition, at 350 nm, the incident photon-to-current efficiency (IPCE) of the BPC photoanode reaches up to 60.45 %, which is much higher than that of pure BiVO₄ (7.75 %). At 0.66 V_RHE, the applied bias photon-to-current efficiency (ABPE) value of BPC photoanode can reach 1.37 %, which is 12.5 times higher than that of pure BiVO₄. This simple and robust strategy provides a pathway to employ photothermal materials to design PEC water splitting photoanodes with excellent overall performance.