Interfacial Bridging Strategy for Charge Extraction/Injection in the BiVO4/CoSn-Layered Double Hydroxide p–n Heterojunction Approach Using Graphene Quantum Dots for Enhanced Water Oxidation Kinetics

The design of a photoanode with a bridging strategy that can enhance the charge injection and transport in a heterojunction can be an efficient approach to separate the photogenerated charge carriers and enhance the water oxidation kinetics. Aiming at such issues, herein we propose a BiVO4/GQDs/CoSn-LDH (layered double hydroxide) photoanode, which leads to the formation of a p–n heterojunction with bridged graphene quantum dots (GQDs) to accelerate the photoelectrochemical (PEC) performance. The BiVO4/GQDs/CoSn-LDH photoanode exhibits a maximum photocurrent density of 4.15 mA/cm2, which is ∼3-fold higher than for the pristine BiVO4 photoanode with an ∼250 mV cathodic shift in the onset potential. A faradaic yield of ∼91% confirms that the obtained photocurrent is mainly due to water oxidation. A mechanistic study based on the electrochemical impedance (EIS), charge separation, and charge injection efficacy measurements reveals that the introduction of GQDs between BiVO4 and CoSn-LDH provides a continuous conducting network to extract holes from the BiVO4 surface and efficiently inject into the CoSn-LDH surface for the water oxidation reaction.