Development of the BiVO4/ZnFe2O4 heterostructure for solar water splitting

Abstract

In this study, we report the development of a BiVO₄/ZnFe₂O₄ heterostructure and its characterization as a photoanode in solar water splitting. ZnFe₂O₄ was deposited on a BiVO₄ thin film after electrodepositing varying charges of FeOOH (50, 100, and 250 mC), which were then thermally oxidized in the presence of air and a zinc source. Structural characterization via XRD and profilometry indicated an increase in film thickness with higher deposited charges. The analysis revealed a decrease in strain and Urbach energy, indicative of reduced structural defects and an increase in the bandgap. SEM images illustrated the porous nature of the film surfaces, with elongated 2D structures enhancing light absorption through multiple reflectance effects. However, increased charge deposition led to particle agglomeration, reducing light absorption efficiency and active surface area, thus diminishing photogenerated charge generation. Electrochemical and photoelectrochemical characterization confirmed the n-type nature of all films, with carrier concentration increasing with film thickness. Nevertheless, the thinnest film (50 mC) exhibited the highest photocurrent, attributed to reduced particle agglomeration, enhanced light absorption, greater charge transport capacity, and superior electrocatalytic behavior, thereby minimizing recombination effects. Overall, the heterostructure demonstrated suitability as a photoanode for oxygen evolution reaction, supported by correct band alignment as determined from flat band potentials.