Dramatically enhanced solar-driven water splitting of BiVO4 photoanode via strengthening hole transfer and light harvesting by co-modification of CQDs and ultrathin β-FeOOH layers

Hydrogen generation by solar-driven water splitting is considered as a promising strategy to address energy crisis and environmental emission issues. Bismuth vanadate (BiVO4) is a highly promising photoanode material for photoelectrochemical (PEC) water splitting, but its severe bulk and surface charge recombination, sluggish oxygen evolution reaction (OER) kinetics and narrow visible light harvesting are still bottlenecks. Here, an excellent CQDs/FeOOH/BiVO4 photoanode was designed by co-modification of carbon quantum dots (CQDs) and ultrathin β-FeOOH layers (<10 nm) on BiVO4 to tackle the above issues. The CQDs/FeOOH/BiVO4 shows dramatically enhanced photocurrent, which is 10.7 and 2.98 times higher than BiVO4 and FeOOH/BiVO4 at 0.8 V vs. RHE (VRHE), with negatively shifted onset potential of 448 and 255 mV, respectively. The maximum incident photon-to-current conversion efficiency (IPCE) of CQDs/FeOOH/BiVO4 is 6.7 and 1.86 times higher than that of BiVO4 and FeOOH/BiVO4, respectively. Additionally, the surface hole injection efficiency (ηsurface) of CQDs/FeOOH/BiVO4 is 7.1 and 2.1 times higher than that of BiVO4 and FeOOH/BiVO4 at 0.8 VRHE, respectively. The results can be attributed to three effects: (i) Synergetic catalysis of CQDs and FeOOH sharply improves the OER kinetics due to the introduction of high-density oxygen vacancies (Ov); (ii) The CQDs/BiVO4 heterojunction efficiently suppresses the bulk charge recombination; (iii) CQDs significantly boost the light harvesting both in the ultraviolet and visible regions.