Mechanism of Incorporation of Zirconium into BiVO₄ Visible-Light Photocatalyst

Monoclinic BiVO₄ is a promising material for realizing low-cost visible-light water splitting. Here, we report the incorporation mechanism of Zr into solution-processed BiVO₄. Characterization of the crystal structure confirmed the incorporation of Zr into the BiVO₄ lattice and the formation of single-phase monoclinic crystals at lower Zr concentrations. Characterization of the electronic stucture suggested that Zr acts as a shallow donor indicated that Zr acts as a shallow donor. The Zr-doped sample showed higher electrical conductivity than the undoped one and significantly enhanced photocatalytic activity at an optimum doping level of 0.1 mol %. Characterization of the local structure around Zr by X-ray absorption spectroscopy revealed a Zr⁴⁺ center in an 8-coordinated dodecahedral environment, indicating incorporation of Zr as a substitute on Bi site in the BiVO₄ host. However, we have found that Zr_Bi substitution generates local lattice distortion, which, in turn, may cause the formation of more oxygen vacancies (V_O) along with Zr_BiV_O defect complexes, thus leading to lower Zr donor efficiency and increased nonradiative recombination. High Zr doping provokes the formation of mixed-phase BiVO₄ crystals, resulting in low photocatalytic activity. The incomplete self-compensation of Zr in BiVO₄ below the solubility limit suggests a potential for substitutional n-type doping of BiVO₄ by group IV elements, paving the way for developing efficient BiVO₄ based-photocatalytic materials.