Fabrication of CoOx/BiVO4 Photoanodes with Enhanced Photoelectrochemical Water Splitting

In this work, the surface of BiVO4 nanoporous films was modified by ultrathin CoOx nanoparticles through a facile electrochemical deposition route. By adjusting the deposition time, the effect of CoOx loading amount (or time) was investigated with respect to the photoelectrochemical (PEC) performance of the BiVO4 photoanode. No significant morphological changes were observed after depositing CoOx cocatalysts onto the BiVO4 surface, except for a rougher surface and the appearance of nanosheets at 40 s. After optimizing the deposition time, the highest photocurrent density of 3.36 mA/cm2 was achieved at 1.23 VRHE for the 20-CB sample under solar irradiation, exhibiting a nearly threefold increase in the photocurrent as compared to that of pristine BiVO4 (1.24 mA/cm2). It was found that the CoOx loading reduced the onset potential and interfacial charge transfer resistance, leading to the significant enhancement of the PEC activity. However, when the deposition time was extended or the loading amount increased, the PEC activity actually decreased, which might be related to the increase in carrier recombination loss. This research will help us understand the mechanism of surface CoOx modification for improving the PEC activity of semiconductor photoanodes like BiVO4.