Enhanced Surface Reaction Kinetics and Charge Separation\nof p–n Heterojunction Co₃O₄/BiVO₄ Photoanodes

Abstract

Surface\nreaction kinetics and bulk charge separation are both critical\nto the efficiency of solar water splitting. In addition to the well-documented\nsurface catalytic effect, the promotion of bulk charge separation\nupon loading of cocatalysts has rarely been reported. This paper describes\nthe synergetic enhancement of surface reaction kinetics and bulk charge\nseparation by introducing discrete nanoisland p-type Co₃O₄ cocatalysts onto n-type BiVO₄, forming a\np–n Co₃O₄/BiVO₄ heterojunction\nwith an internal electric field to facilitate charge transport. Being\nhighly dispersed on the surface of photoanodes, the nanoisland cocatalysts\ncould suppress the formation of recombination centers at the photoanode/cocatalyst\ninterface. This cocatalyst-loading method achieved a charge separation\nefficiency of up to 77% in the bulk and 47% on the surface of catalysts.\nAn AM 1.5G photocurrent of 2.71 mA/cm² at 1.23 V versus\nthe reversible hydrogen electrode for water oxidation was obtained,\nwhich is the highest photocurrent yet reported for Co-catalyzed undoped\nBiVO₄ photoanodes, with a photoconversion efficiency of\n0.659%.