A Zn:BiVO4/Mo:BiVO4 homojunction as an efficient photoanode for photoelectrochemical water splitting

Abstract

Photoelectrochemical (PEC) water splitting has been extensively studied as a method to convert sunlight and water to hydrogen. Among the many obstacles facing PEC water splitting, a critical challenge is the lack of efficient photoanodes for the water oxidation reaction. Here, we report an n–n⁺ type-II homojunction of Zn:BiVO₄/Mo:BiVO₄, which improves the bulk transport and surface charge transfer processes of the well-studied BiVO₄ photoanode. In this homojunction, the Zn and Mo dopants move the BiVO₄ valence band maximum and conduction band minimum, respectively, closer to the Fermi level, establishing an n–n⁺ type-II homojunction. The staggered band alignment between Zn:BiVO₄ and Mo:BiVO₄ facilitates electron–hole separation between the two layers. The Mo dopant increases the donor concentration, leading to higher electrical conductivity. The Zn dopant increases the number of oxygen chemisorption sites, improving the interfacial charge transfer process. With additional deposition of the oxygen evolution electrocatalyst Ni:FeOOH, the homojunction achieves charge transport and transfer efficiencies of 65% and 89%, respectively. The final Ni:FeOOH/Zn:BiVO₄/Mo:BiVO₄ photoanode achieves a photocurrent density of 2.7 mA cm⁻² and a faradaic efficiency for oxygen evolution of ∼92% at 1.23 V vs. RHE in the electrolyte of potassium buffer solution (pH ∼ 7).