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

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).