Photothermal-enhanced solar water oxidation on NiO/amorphous carbon/BiVO4 and CoOx/amorphous carbon/BiVO4 photoanodes

Water oxidation is an endothermic reaction; BiVO4-based photoanodes with good photothermal and catalytic properties would be propitious to achieve efficient water oxidation in theory. Herein, NiO/amorphous carbon/BiVO4 (NiO/C/BiVO4) and CoOx/amorphous carbon/BiVO4 (CoOx/C/BiVO4) films were prepared by a facile candle flame roasting approach, and further investigated as photoanodes for solar water oxidation. Compared to BiVO4 and C/BiVO4 photoanodes, better water oxidation performance was achieved on the CoOx/C/BiVO4 and NiO/C/BiVO4 photoanodes. At 1.23 V vs. RHE, the water oxidation photocurrent of the CoOx/C/BiVO4 and NiO/C/BiVO4 photoanodes was 2.32 and 2.41 times higher than that of the BiVO4 photoanode, respectively. The water oxidation activity on the CoOx/C/BiVO4 and NiO/C/BiVO4 photoanodes can be well maintained in the range of 84–87% after 120 min of constant reaction, which is higher than that on the BiVO4 photoanode (43% activity retained). The NiO/C/BiVO4 and CoOx/C/BiVO4 photoanodes having higher water oxidation performance can be attributed to the following integrated effects. (1) The p–n heterojunction effect of NiO/BiVO4 and CoOx/BiVO4 drives the directional transfer of holes to CoOx or NiO and weakens the carrier recombination on BiVO4. (2) Amorphous carbon, CoOx and NiO absorb and convert the long wavelength light (λ > 510 nm) into heat to improve the co-catalysis performance of CoOx and NiO, and enable the NiO/C/BiVO4 and CoOx/C/BiVO4 photoanodes for efficient water oxidation. The present work provides two effective BiVO4-based photoanodes for photothermal-enhanced water splitting, which could inspire the design and development of similar materials for photothermal-enhanced solar water splitting.