Electrodeposited Cr-Doped α-Fe2O3 thin films active for photoelectrochemical water splitting

Abstract

Polycrystalline hematite (α-Fe2O3) Chromium (Cr)-doped thin films were electrodeposited on fluorine-doped tin oxide-coated glass substrates. The electrodeposition bath comprised an aqueous solution containing FeCl3·6H2O, NaCl, and H2O2.Chromium was added to the electrolyte at such a proportion that the Cr/(Cr + Fe) ratio remained within the 2–8 at. % range. The as-deposited films were subsequently annealed in air at 650 °C for 2 h. The structure and morphological characteristics of the undoped and Cr-doped α-Fe2O3 thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV–Vis spectroscopy. Cr doping led the main XRD lines to shift to lower angles, which mostly resulted from substituting Fe3+ for Cr4+ ions that leads to α-Fe2O3 lattice contraction. The SEM observations showed that the roughness and aspect of surfaces changed with the Cr doping level. The photoelectrochemical (PEC) performance of the α-Fe2O3 films was examined by chronoamperometry and linear sweep voltammetry techniques. The Cr-doped films exhibited greater photoelectrochemical activity than the undoped α-Fe2O3 thin films. The highest photocurrent density was obtained for the 8% Cr-doped α-Fe2O3 films in 1 M NaOH electrolyte. All the samples achieved their best IPCE at 400 nm. The IPCE values for the 8 at.% Cr-doped hematite films were 20-fold higher than that of the undoped sample.This Cr-doped hematite films ‘excellent photoelectrochemical performance was mainly attributed to improved charge carrier properties. Such high photoactivity was attributed to the large active surface area and increased donor density caused by increasing the Cr doping in the α-Fe2O3 films.