CQDs hole transport layer enhanced photocatalytic performance of BiVO₄-based type II heterojunctions for water splitting

Abstract

Bismuth vanadate (BiVO4) has emerged as a highly competitive photoanode candidate for photoelectrocatalytic water splitting. Nevertheless, its practical application is severely hindered by critical drawbacks, including serious surface recombination of photogenerated carriers and sluggish water oxidation kinetics. To address these bottlenecks, this work reports an innovative hierarchical heterostructure photoanode rationally designed and constructed on fluorine-doped tin oxide (FTO) substrates. The novel photoanode integrates Mo/W co-doped spinel BiVO4 (MW:BVO), nitrogen-doped CoFe2O4 three-dimensional nanospheres (N:CFO), and carbon quantum dots (CQDs) into a well-defined MW:BVO/N:CFO/CQDs heterojunction. Distinctively, the CQDs serve as an efficient hole transport layer, which synergizes with the type II heterojunction to substantially suppress electron–hole pair recombination and drastically accelerate water oxidation kinetics. Impressively, under 1.23 V vs. RHE and 1.5 G simulated sunlight irradiation, the optimized photoanode delivers a remarkable photocurrent density of 5.31 mA/cm2, a 5.96-fold enhancement relative to the pristine metal-ion-doped BiVO4 photoanode. Moreover, the maximum applied bias photon-to-current efficiency (ABPE) is boosted from 0.078% to 0.63% after loading the N:CFO/CQDs cocatalyst. These findings demonstrate that the elaborately designed N:CFO/CQDs cocatalyst system effectively facilitates the separation and migration of photogenerated carriers, offering a new and feasible strategy to elevate the photoelectric conversion and photoelectrocatalytic performance of BiVO4-based photoanodes.