Elucidation of the structural and charge separation properties of titanium-doped hematite films deposited by electrospray method for photoelectrochemical water oxidation

Abstract

Elemental doping is considered to be an effective strategy to improve the photoelectrochemical (PEC) activity of hematite (α-Fe2O3) as a photoanode for water splitting, but the precise function (s) of the dopant remains unclear. In this study, we report on the structural and charge separation properties of titanium-doped hematite (Ti doped Fe2O3) films prepared by a simple electrospray technique for PEC water oxidation. The effect of Ti doping on the structure, morphology, light absorption, and electrical and photoelectrochemical properties was investigated on α-Fe2O3 films. SEM images revealed a reduction in particle sizes for 2% Ti doped α-Fe2O3, while an increase in particle size was observed for higher Ti content. XRD confirmed the presence of α-Fe2O3 without any impurity or other phases. From XPS spectra, the incorporation of Ti was confirmed in the form of Ti4+ as predominant species while no impurities from the substrate were detected. When the Ti doped Fe2O3 (2% Ti) film was used as a photoanode in a PEC cell, it delivered the best performance with a maximum photocurrent density of 1.09 mA cm−2 (at 1.8 V vs. RHE and under standard 1 sun illumination conditions (AM 1.5 G, 100 mW cm−2)), which is 2 times higher than that of the un-doped α-Fe2O3 (0.51 mA cm−2). The photoelectrode also showed a superior incident photon to current efficiency (IPCE) as compared to an un-doped α-Fe2O3. This enhancement in performance was attributed to the better charge separation and transport properties of α-Fe2O3 due to Ti doping, as revealed by an electrochemical impedance spectroscopy (EIS) analysis.