Enhanced Photoelectrochemical Water Oxidation on BiVO4 with Mesoporous Cobalt Nitride Sheets as Oxygen-Evolution Cocatalysts

A series of cobalt-based oxide and nitride sheet electrocatalysts were developed and then coupled with BiVO4 to investigate the cocatalytic effect and the relationship between electrocatalysis and photoelectrochemical (PEC) water oxidation. The cobalt nitride sheets were synthesized by a hydrothermal method before calcination in ammonia and show superior electrocatalytic activities for oxygen evolution. BiVO4 has been reported to be a desirable candidate among semiconductor materials for photoelectrochemical water splitting except for its sluggish surface oxygen-evolution kinetics. In this work, the PEC performance of BiVO4 was significantly enhanced by efficient oxygen-evolution catalysts serving as cocatalysts. The enhancement of the PEC performance after cocatalyst loading agrees well with the electrocatalytic activities and can be ascribed to the improved surface kinetics. The photocurrent characteristics combined with the results of the electrochemical tests indicate that favourable overpotential and Tafel slope are both important factors in the role of cocatalysts for efficient photoelectrochemical water oxidation. Benefiting from the cocatalytic effect, Co2N0.67-loaded BiVO4 exhibited the highest photocurrent of 2.21 mA/cm(2) at 1.23 V vs. RHE, which is about 80% higher than that of bare BiVO4.