On the Origin of Enhanced Surface Reaction Kinetics and Charge Separation for p-n Hheterojunction on Co3O4/BiVO4 Photoanodes

Surface reaction kinetics and bulk charge separation are both critical to the efficiency of solar water splitting. In addition to the well documented surface catalytic effect, the promotion of bulk charge separation upon the loading of cocatalysts has rarely been reported. This talk describes the synergetic enhancement of surface reaction kinetics and bulk charge separation by introducing discrete nano-island p-type Co₃O₄ cocatalysts onto n-type BiVO₄, forming p-n Co₃O₄/BiVO₄ heterojunction with internal electric field to facilitate charge transport. Being highly dispersed on the surface of photoanodes, the nano-island cocatalysts could suppress the formation of recombination centers at the photoanode/cocatalyst interface. This cocatalyst loading method achieved a charge separation efficiency of up to 77% in the bulk and 47% on the surface of catalysts. An AM 1.5 photocurrent of 2.71 mA/cm² at 1.23 V versus the reversible hydrogen electrode for water oxidation was obtained, which is the highest photocurrent yet reported for cobalt catalyzed undoped BiVO₄ photoanodes, with a photoconversion efficiency of 0.659%.