Molecular Cobalt-based Complexes As Precursors Of Cocatalyst For BiVO₄ Photoanodes Modification

Efficient water oxidation represents one of the major challenges to solar water splitting. Bismuth vanadate （BiVO₄） has a band structure that is suitable for potential use as photoanode, but it suffers from poor electron-hole separation. It has been reported that BiVO₄ electrode coupled with cobalt oxide to enhance the photoelectrochemical （PEC） performance for water oxidation. We represent here a series of molecular cobaloximes complexes that can serve as precursors to form nanostructured and amorphous cobalt-based thin films during electrodeposition. These catalyst films were deposited at 1.5V （vs Ag/AgCl） from neutral phosphate buffer solutions containing 1mM cobaloximes. Five catalyst films （CoO_x-1-CoO_x-5） were synthesized from various cobaloximes. The use of different complexes allow to control over the deposition rate and morphology, thus enable the production of thin, highly active catalyst films. The best photocurrent density is 3.5 mA/cm2 for water oxidation in a 0.1 M phosphate buffer solution （pH= 7.0） under AM 1.5G illumination, which is higher than the photocurrent densities obtained by other CoO_x under the same condition and the highest photocurrent density for undoping BiVO₄ coupled with CoO_x so far. The sample deposited from Co（NO₃）₂ has 11 times higher amount of Co per unit area than that deposited from Co（dmgBF₂）2（OH₂）₂, when both get the optimal current density at 1.23V vs. RHE. The result illustrates that Co on the film derived from Co（dmgBF₂）₂（OH₂）₂ has a higher utilization rate for water oxidation.