Identifying dual functions of rGO in a BiVO4/rGO/NiFe-layered double hydroxide photoanode for efficient photoelectrochemical water splitting

Abstract

Bismuth vanadate (BiVO₄) is a promising material for photoelectrochemical (PEC) water oxidation. However, the sluggish water oxidation kinetics, poor electron transport properties and severe charge recombination limit its performance. Here, a new type of triadic photoanode is developed by rationally designing the electrode structure. The NiFe-layered double hydroxide (NiFe-LDH) serves as a water oxidation catalyst (WOC) to accelerate the transportation of the photo-generated holes from the BiVO₄ photoelectrode to the electrolyte for improving the water oxidation reaction, while the reduced graphene oxide (rGO) nanosheets serve as an efficient electron shuttling mediator for suppressing the electron–hole recombination at the BiVO₄/NiFe-LDH interfaces. On the other hand, rGO can positively shift the electrodeposion potential of NiFe-LDH (−0.1 V vs. RHE) which can greatly protect the BiVO₄ electrode, since a more negative potential would reduce its PEC activity. This electrode exhibits a significantly higher photocurrent density than those of its pristine BiVO₄, BiVO₄/rGO, and BiVO₄/NiFe-LDH counterparts, producing a photocurrent density of 3.26 mA cm⁻² at 1.23 V vs. RHE under AM 1.5 G illumination and showing excellent stability. The improved PEC performance is attributed to the accelerated charge separation/transfer between the photoanode/electrolyte interfaces and surface water oxidation reaction due to the synergistic effect of rGO and NiFe-LDH.