Photothermal effect of carbon quantum dots enhanced photoelectrochemical water splitting of hematite photoanodes

Abstract

Hematite (α-Fe₂O₃), as one of the most promising photoanode materials, exhibits localized small polaron carrier conduction, resulting in low minority carrier transport. An elevation in operating temperature is found to activate minority carrier hopping in metal oxide photoanodes. Here, the photothermal effect of carbon quantum dots (CQDs) is introduced in the PEC water splitting process. Upon NIR light irradiation, the temperature of the CQDs/Fe₂O₃/TiO₂ photoanode is increased instantly due to the photothermal conversion, thereby stimulating the charge transport in the bulk of the photoanode. Cobalt-phosphate (Co-Pi) acting as an oxygen evolution cocatalyst is deposited on the surface of the photoanodes to accelerate the water oxidation kinetics, and its catalytic activity is also promoted due to the temperature elevation. Consequently, a remarkable photocurrent of ∼3.0 mA cm⁻² at 1.23 V versus a reversible hydrogen electrode (V_RHE) for the judiciously designed Co-Pi/CQDs/Fe₂O₃/TiO₂ photoelectrodes is achieved under NIR light irradiation. These findings verify that the introduction of the photothermal effect is simple yet general, providing a unique platform to capitalize on the photothermal characteristics to boost the PEC performance of photoelectrodes.