A MnFe2O4/BiVO4 film photoanode with heterojunction, co-catalytic and photothermal effects for effective solar water oxidation

Abstract

To modify the solar water splitting performance of BiVO₄ photoanodes, the search for effective co-catalysts with photothermal conversion and p-type semiconductor properties is significant. Herein, spinel MnFe₂O₄ nanoparticles were selected as co-catalysts and coupled on BiVO₄ film to form a MnFe₂O₄/BiVO₄ film photoanode for solar water oxidation. Relative to a BiVO₄ film photoanode, the MnFe₂O₄/BiVO₄ film photoanode achieved higher activity, faster kinetics and better stability for solar water oxidation. At 1.23 V vs. RHE, the water oxidation photocurrent on the MnFe₂O₄/BiVO₄ film photoanode was 2.58 mA cm⁻², which was more than twice that on the BiVO₄ film photoanode (1.06 mA cm⁻²). In addition, the MnFe₂O₄/BiVO₄ film photoanode showed stable activity in solar water oxidation for 2 h of reaction. The higher solar water oxidation performance of the MnFe₂O₄/BiVO₄ film photoanode mainly stemmed from the synergism of its p–n heterojunction, co-catalytic and photothermal effects. Specifically, MnFe₂O₄ nanoparticles coupling on BiVO₄ film can form p–n heterojunctions, which could promote the separation and transfer of carriers, and more holes could drive water oxidation. Meanwhile, spinel MnFe₂O₄ nanoparticles can capture some solar light to produce heat due to their photothermal properties, which is beneficial to the achievement of endothermic water oxidation. Furthermore, the co-catalytic properties of spinel MnFe₂O₄ could boost the water oxidation activity and kinetics. As a synergism result, higher solar water oxidation performance was achieved for the MnFe₂O₄/BiVO₄ film photoanode.