Aerosol-assisted facile fabrication of bimetallic Cr2O3–Mn2O3 thin films for photoelectrochemical water splitting

Abstract

In the present studies, we demonstrate a simple and efficient method to fabricate Cr₂O₃–Mn₂O₃ composite thin films of immaculate homogeneity for photoelectrochemical (PEC) study. The clear THF solution of chromium(II) acetate hydrate and manganese(II) acetate tetrahydrate precursors in a 1 : 1 mole ratio was used in the aerosol-assisted chemical vapor deposition (AACVD) over FTO-coated glass substrates at the temperatures of 400, 450, and 500 °C in ambient argon conditions. X-ray powder diffraction (XRD), field emission scanning electron microscopy (FESEM), and energy dispersive X-ray (EDX) analyses verified the formation of uniformly dispersed crystalline Cr₂O₃ and Mn₂O₃ phases. Direct optical band gaps at 2.50, 2.39, and 2.10 eV were measured at 400, 450, and 500 °C, respectively, from UV-Vis spectrophotometry. X-ray photoelectron spectroscopy (XPS) was carried out to investigate the oxidation state of the constituent elements in the prepared sample. PEC studies revealed that the synergistic effect appeared between Cr₂O₃ and Mn₂O₃ phases to facilitate the photo-oxidation of water, leading to a photocurrent density of 1.25 mA cm⁻² at 1.23 V vs. RHE. The Cr₂O₃–Mn₂O₃ composite thin film at 500 °C having a more compact structure shows the highest photocurrent density among all samples (0.32 mA cm⁻² at 1.23 V vs. RHE for 400 and 450 °C). Kinetics of the photocatalysis were investigated by electrochemical impedance spectroscopy (EIS), and a decrease in charge transfer resistance (R_ct) was observed with the rise in deposition temperature. Deposition at different temperatures resulted in the improvement of photocatalytic activity, and these findings may lead to advantageous modification in the fabrication of thin film photoelectrodes for PEC water splitting.