Influence of the Physical, Structural and Chemical Properties on the Photoresponse Property of Magnetron Sputtered TiO<SUB>2</SUB> for the Application of Water Splitting

Abstract

The production of hydrogen from water (called "water splitting"), utilises sunlight as an energy source (solar-hydrogen) in a photoelectrochemical (PEC) solar cell, is a promising source of green energy. In this work, a PEC was used, for evaluating the photoactivity of a thin film TiO2 based photoanode by measuring photocurrent (which is comparable to hydrogen production rate by water splitting process in PEC). The main focus of this work is to study the effect of the TiO2 nanosurface and bulk properties on the photoresponse properties of the photoanode. The TiO2 coatings (360-400 nm) were deposited using a closed field reactive magnetron sputtering system. The structure and morphology of the TiO2 coatings were systematically altered by varying the deposition pressure between 5 x 10(-4) to 1 x 10(-2) mbar. The properties of the deposited nano-coatings were determined using Ellipsometry, SEM, AFM, profilometry, XPS, Raman and X-ray diffraction (XRD). Coating properties were correlated with the light absorption and photocurrent performance which were evaluated using UV-Vis spectroscopy and tri-electrode potentiostat measurements respectively. It was concluded from this study that the coating deposition pressure has a pronounced effect on the TiO2 photoanode properties leading to a significant enhancement in the photoactivity in PEC cell. Over a six fold increase in photocurrent at applied potential 0 V was observed for TiO2 photoanode prepared at 4 x 10(-3) mbar as compared to 5 x 10(-4) mbar. A correlation has been established between the deposition pressure, nano surface morphology and bulk properties, UV-Vis light absorbance and bandgap value, and the consequently higher (i) photocurrent density, (ii) negative flat band, and (iii) open circuit potential measured in Photoelectrochemical (PEC) cell.