Surface grooved visible light active carbon modified (CM)-n-TiO2 thin films for efficient photoelectrochemical splitting of water

Carbon modified n-type titanium oxide (CM-n-TiO2) photoelectrodes were synthesized by thermal flame oxidation of grooved and non-grooved Ti metal sheet at several flame temperatures for different lengths of time. The photoresponse of CM-n-TiO2 was evaluated by measuring the rate of water splitting to hydrogen and oxygen, which is proportional to observed photocurrent density. The optimized grooved CM-n-TiO2 photoelectrodes generated photocurrent density of 11.45 mA cm−2 at applied potential of 0.242 V at illumination intensity of 100 mW cm−2 from a 150 W xenon lamp. However, under the same illumination condition the non-grooved sample generated photocurrent density of 9.17 mA cm−2 at applied potential of 0.24 V. The maximum photoconversion efficiencies obtained from wavelength dependent monochromatic photocurrents were found to be 11.16% and 8.86% for grooved and non-grooved samples, respectively, under the same illumination intensity from the xenon lamp. Importantly, for optimized grooved CM-n-TiO2 sample, at an applied potential of 0.242 V the total conversion efficiency of 9.5% and the maximum photoconversion efficiency of 7.62% for water splitting under global air mass of 1.5 (AM 1.5) sunlight (1 sun) illuminations were observed. The carbon contents in optimized grooved and non-grooved CM-n-TiO2 samples were found to be 19.38 at.% and 17.60 at.%, respectively, from energy dispersive analysis by X-ray (EDAX) though both samples showed same band gap energy of 2.65 eV and a mid-gap band of 1.4 eV above the valence band. The UV-Vis spectra, X-ray diffraction (XRD) spectra and scanning electron micrograms (SEM) of these samples were also given.