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

Abstract

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 CoO_x/amorphous carbon/BiVO₄ (CoO_x/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 CoO_x/C/BiVO₄ and NiO/C/BiVO₄ photoanodes. At 1.23 V vs. RHE, the water oxidation photocurrent of the CoO_x/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 CoO_x/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 CoO_x/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 CoO_x/BiVO₄ drives the directional transfer of holes to CoO_x or NiO and weakens the carrier recombination on BiVO₄. (2) Amorphous carbon, CoO_x and NiO absorb and convert the long wavelength light (λ > 510 nm) into heat to improve the co-catalysis performance of CoO_x and NiO, and enable the NiO/C/BiVO₄ and CoO_x/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.