Cobalt polyoxometalate on N-doped carbon layer to boost photoelectrochemical water oxidation of BiVO4

Abstract

• Ternary BiVO 4 -N/C-CoPOM photoanode is constructed. • High photocurrent density of 3.30 mA cm −2 and low onset potential are achieved. • Much higher applied bias photon-to-current efficiency and fill factor are achieved after depositing CoPOM. • Charge injection efficiency is greatly improved after depositing CoPOM. Photoelectrochemical (PEC) water splitting can convert solar power into clean energy carrier of hydrogen, which is a promising strategy to address the global energy crisis and environmental issues. At present, the sluggish kinetics of the separation and migration of the photo-excited electrons and holes for water oxidation is the bottleneck for the high solar-to-hydrogen efficiency in this field. Herein, we exploit cobalt polyoxometalate (CoPOM) as a novel molecular cocatalyst locating at N-doped carbon (N/C) to boost the charge separation and injection of BiVO 4 photoanodes for PEC water oxidation. Comprehensive results reveal that the uniformly distributed CoPOM specially improves the hole injection efficiency, leading to the lower onset potential of water oxidation and confirming the improved the kinetics of BiVO 4 photoanode for PEC water splitting. A high maximum applied bias photon-to-current efficiency of 1.22% is achieved at a low potential of 0.63 V vs . reversible hydrogen electrode (RHE) for BiVO 4 -N/C-CoPOM, and the photocurrent density of increases up to 1.93 mA cm −2 at 0.63 V vs . RHE and 3.30 mA cm −2 at 1.23 V vs . RHE, which are 11.4 and 5.4 times higher than that of the pristine BiVO 4, respectively. Particularly, the significantly improved PEC performance in the low bias range indicates CoPOM can effectively reduce the water oxidation energy barrier. We believe this research provides a novel molecular cocatalyst of POM for the improvement of PEC performance of photoanode, and expands the scope for the design of efficient cocatalysts for solar energy-conversion devices.