TiO2-based homojunction photo-electrode for solar-driven water splitting

Since the initial demonstration of successful water splitting on the surface of illuminated TiO2 in 1972, research efforts have overwhelmingly focussed on addressing the relatively large band gap of TiO2 in order to achieve commercially viable, solar-hydrogen production performance. Consequently, other performance related issues, such as inadequate charge separation, have been overlooked. As outlined in this review, the challenge of achieving high performance solar-driven water splitting requires a more holistic approach than simply targeting individual functional properties in isolation. Here it has been shown how the benefits of doping for band gap narrowing purposes may be realised by simultaneously assuring efficient charge separation via the utilisation of a photo-electrode design that incorporates a homojunction. This novel concept is based upon observations of charge separation behaviour during the illumination of segregation-induced composition gradients in donor-doped TiO2. It has been proposed that a high performing TiO2-based photo-electrode may be attained through the construction of a multilayered thin film material whose composition is conveniently controlled as a function of depth. Thereby providing the means to tune both the optical absorption, and charge separation properties simultaneously.