Oxygen vacancy-abundant carbon quantum dots as superfast hole transport channel for vastly improving surface charge transfer efficiency of BiVO4 photoanode

The efficiency of hole extraction and transfer at electrode/electrolyte interface is one of the most important bottlenecks of BiVO4 photoanodes for photoelectrochemical (PEC) water splitting. Here, a huge improvement of surface charge transfer efficiency (ηsurface) of BiVO4 photoanode was achieved by surface modification of oxygen vacancy-abundant carbon quantum dots (OV-CQDs), in which the OV-CQDs serve as superfast hole transport channel for the fact that the abundant OV in OV-CQDs could induce the outward driving force for hole trapping and migration at electrode/electrolyte interface. The OV-CQDs/BiVO4 shows the ηsurface value of 74.3% at 0.65 V vs. RHE (VRHE), which is 7.1 and 3.3 times higher than BiVO4 and CQDs/BiVO4, respectively. Besides, the OV-CQDs efficiently promote the bulk charge separation and UV-vis light harvesting of BiVO4. Therefore, the OV-CQDs/BiVO4 exhibits remarkable photocurrent densities of 2.76 mA cm−2 at 0.65 VRHE and 4.01 mA cm−2 at 1.23 VRHE, which are 12.5 and 3.4 times higher than BiVO4, 3.5 and 2.6 times higher than CQDs/BiVO4, respectively.