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 (In 2 O 3 ) semiconductor (SC) through chemical bath synthesis using In(NO 3 ) 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 In 2 O 3 as 3.60 eV along with an indirect gap of 2.78 eV. Scanning electron microscopy reveals the agglomerated nature of In 2 O 3 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 In 2 O 3 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 H 2 O → O 2 oxidation reaction (in 0.1 M Na 2 SO 4 - 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.