Effect of cation configuration and solvation on the band positions of zinc ferrite (100)

Abstract

Zinc ferrite ZnFe_{2}O_{4} belongs to the spinel-type ferrites that have been proposed as photocatalysts for water splitting. The electronic band gap and the band edge positions are of utmost importance for the efficiency of the photocatalytic processes. We, therefore, calculated the absolute band energies of the most stable surface of ZnFe_{2}O_{4}, the Zn-terminated (100) surface at self-consistent hybrid density functional theory level. The effect of Fe- and Zn-rich environments, cation exchange as antisite defects and implicit solvation on the band positions is investigated. Calculated flat band potentials of the pristine surface model ranges from -0.9 to -0.8 V against SHE in vacuum. For Zn-rich (Fe-rich) models this changes 0.3–0.9 (0.0–0.7) V against SHE. Fe-rich models are closest to the experimental range of reported flat band potentials. Solvent effects lower the calculated flat band potentials by up to 1.8 eV. The calculated band gaps range from 1.5 to 2.9 eV in agreement with previous theoretical work and experiment. Overall, our calculations confirm the experimentally observed low activity of ZnFe_{2}O_{4} and its dependence on preparation conditions.Graphical abstract