Effect of Facet-Selective Assembly of Cocatalyst on BiVO4 Photoanode for Solar Water Oxidation

Rational assembly of cocatalysts on crystal-based photocatalysts with anisotropic facets, namely the reduction cocatalyst on the reduction facets and oxidation cocatalyst on the oxidation facets, can enhance the photocatalytic activity remarkably. However, this strategy of selective loading of cocatalysts on crystal-facet engineered photoelectrodes is rarely discussed in photoelectrocatalysis (PEC). Herein, we fabricated BiVO4 microcrystal photoanodes with simultaneous exposure of oxidation {110} and reduction {010} facets to study the effect of facet-selective assembly of cocatalysts on the activity of PEC water oxidation. By elaborative photodeposition, identical cocatalysts of MnOx were selectively loaded on the reduction, the oxidation and all the facets of BiVO4 photoanodes (respectively designated as R-BVO, O-BVO and O/R-BVO). We found that MnOx facilitates the charge separation in BiVO4 more significantly on the oxidation facets than on the reduction ones, contributing to the net increase in photocurrent of O-BVO being as 5.2 and 2.2 times that of R-BVO and O/R-BVO, respectively. Surface photovoltage analysis reveals that the interaction between the inherent built-in electric field in BiVO4 crystals and the additive electric filed induced by the MnOx was account for the difference. Our work emphasizes the effect of facet-selective assembly of cocatalyst in PEC systems, which may guide the rational design of highly efficient photoelectrodes for solar energy conversion.