Enhancement of BiVO4 photoanode surface oxygen evolution kinetics via Ni-Fe-ZIF derived bimetallic NiFeOx co-catalyst for water oxidation

The water oxidation kinetics on the surface of bismuth vanadate (BiVO₄) photoanode is slow and the surface charge recombination is serious which hindering the photoelectrochemical (PEC) water splitting process. To enhance the PEC performance of BiVO₄ and expedite the water oxidation process, in this work, a straightforward electrostatic adsorption and pyrolysis methods were devised to convert bimetallic Ni-Fe-zeolitic imidazolate frameworks (Ni-Fe-ZIF) molecular sieve into NiFeO_x oxygen evolution co-catalyst and modified on BiVO₄ photoanode surface (NiFeO_x/BiVO₄). The optimized NiFeO_x/BiVO₄ photoanode showed a high optical photocurrent density of 3.57 mA/cm² at 1.23 V compared with reversible hydrogen electrode under AM 1.5G illumination with 4.4 times compared to the pure BiVO₄ photoanode. The NiFeO_x/BiVO₄ composites photoanodes also exhibited the higher charge transfer efficiency of more than 77.8 % than the pure BiVO₄ photoanode, indicating that the NiFeO_x has excellent co-catalytic properties during PEC process. The improvement of photoelectric conversion efficiency can be attributed to the presence of NiFeO_x layer with oxygen vacancies and more metal active sites on the BiVO₄ surface which promoted the separation and transport of photoelectron-hole pairs and the surface oxygen evolution kinetics, thus significantly improving the photocurrent density.