Temperature controlled fabrication of chemically synthesized cubic In2O3 crystallites for improved photoelectrochemical water oxidation

Abstract

The present paper describes the development of indium (III) oxide (In2O3) semiconductor (SC) through chemical bath synthesis using In(NO3)3 as a precursor followed by annealing in air at various high temperatures (600–900 °C). Thin films were prepared over F-doped tin oxide (FTO) coated glass substrate using suspension of the SC powders in ethylene glycol followed by drying at 600 °C. Absorption spectrum measures the direct band gap of In2O3 as 3.60 eV along with an indirect gap of 2.78 eV. Scanning electron microscopy reveals the agglomerated nature of In2O3 particle whereas X-ray diffraction analysis confirms presence of cubic crystallites with preferably (222) orientation. With the gradual rise in annealing temperature (600–900 °C), the size of the crystallites as well as their quality improves, as evident through transmission electron microscopy and PL emission spectra. The In2O3 semiconductor thin films exhibit significant photoelectrochemical activity and long term stability in terms of oxygen evolution reaction from water. The sample annealed at an optimized temperature of 800 °C exhibits the highest photo-current of 1.15 mA cm−2 for H2O → O2 oxidation reaction (in 0.1 M Na2SO4 - pH7, PBS), at 1.51 V vs. RHE (1.23 V vs. NHE) under illumination of 35 mW cm−2. Electrochemical impedance spectra (Mott-Schottky) analysis confirms n-type conductivity for the semiconductors, whereas the action spectra suggest ∼40% incident photon to current conversion efficiency (IPCE) for the optimized materials.