A BiVO4/Bi2Mo2O9 heterostructure towards oriented charge transfer for efficient photoelectrochemical water oxidation†

The sluggish transfer of photogenerated charges is an intrinsic problem in the photoelectrochemical (PEC) conversion of solar energy into chemical energy. Constructing nanostructured heterostructure photoelectrodes is one of the most effective strategies for achieving energetic charge transfer kinetics. Herein, we fabricate a type II heterostructure film of BiVO₄/Bi₂Mo₂O₉ for PEC water splitting using the successive ionic layer adsorption and reaction (SILAR) method. Owing to the work function difference of ∼230 mV between the two semiconductors, free electrons will flow from Bi₂Mo₂O₉ to BiVO₄, causing positive charges to accumulate on the Bi₂Mo₂O₉ side and negative charges on the BiVO₄ side. This charge redistribution induces a built-in electric field pointing from Bi₂Mo₂O₉ to BiVO₄, facilitating the separation of photogenerated electrons and holes. Consequently, the corresponding photocurrent density in the BiVO₄/Bi₂Mo₂O₉ photoanode reaches 0.61 mA cm⁻², which is 3.4 times that of bare Bi₂Mo₂O₉ (0.18 mA cm⁻²) at 1.23 V vs. the Reversible Hydrogen Electrode (RHE). The interface charge interaction results in upward and downward band bending toward the interface for Bi₂Mo₂O₉ and BiVO₄ and also leads to enhanced oxidation kinetics (70.1%) and high photovoltage (340 mV).