Development of ternary iron vanadium oxide semiconductors for applications in photoelectrochemical water oxidation

Abstract

Herein, we report the synthesis of Fe–V-oxides via the drop casting of metal precursor solutions in different proportions onto an indium tin oxide (ITO) coated glass followed by annealing in air at 500 °C for 3 h. UV-vis spectroscopy of the Fe–V-oxides indicates absorption due to ‘direct’ and ‘indirect’ band gaps, although Fe-oxide shows a direct band gap nature. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX) and X-ray diffraction (XRD) studies reveal different surface morphologies with variable crystalline phases for the Fe₂O₃, FeVO₄, FeV₂O₄ and Fe₂VO₄ semiconductors. The photoelectrochemical (PEC) water oxidation reaction over the different materials reveals that the FeV₂O₄ semiconductor exhibits the maximum photocurrent of 0.18 mA cm⁻² at an applied bias of +1.0 V (vs. Ag/AgCl) under the illumination of 100 mW cm⁻² compared to the other Fe₂O₃, FeVO₄ and Fe₂VO₄ semiconductors. Electrochemical impedance spectroscopic (Mott–Schottky) analysis confirms n-type semiconductivity for all the materials with highest donor density, in the order of 2.7 × 10²⁰ cm⁻³, for the FeV₂O₄ thin film, and PL spectra are useful for measuring the separation efficiency of the photo-generated charge carriers. Chronoamperometric studies under constant illumination of the best semiconductor (FeV₂O₄) indicate the significant stability of the material, and photoelectrochemical action spectra demonstrate 22% incident photon to current conversion efficiency (IPCE) and 60% absorbed photon to current conversion efficiency (APCE).