Photoelectrocatalytic activity of In(iii)-modified TiO2 photoanodes in the visible spectrum region

Abstract

Nanocrystalline film photoanodes of titanium dioxide modified with In(III) ions in the concentration range from 1.0 to 10 mass% (0.23 to 2.52 at%) are manufactured using the sol–gel method. Their physicochemical characteristics and the structure of In-containing compounds on the TiO₂ surface are investigated via transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and UV-vis absorption spectroscopy. The photoelectrocatalytic activity of these anodes in the reactions of methanol and formic acid electrooxidation studied under illumination with monochromatic light (369 and 461 nm; 7.5 and 10 mW cm⁻², respectively) and visible light (a sunlight simulator; 100 mW cm⁻²) is shown to decrease symbatically with an increase in indium content. It is also shown that a selective photoelectrooxidation of methanol is observed for titanium dioxide modified with 0.23 at% In in a potential region of (−780 ÷ −550 mV). Using photocurrent modulation spectroscopy (IMPS), the recombination rate constants and the charge carrier transfer efficiency are determined under illumination of the modified photoanode with monochromatic light (369 nm; 7.5 mW cm⁻²) at a potential of −0.8 V in a solution of 0.1 M KOH containing methanol. It is demonstrated that the doping of titanium dioxide with 0.23 at% In promotes both an increase in the current of electron–hole pair generation and a decrease in recombination losses.