Titanium dioxide, TiO2, has a wide range of applications as a photocatalyst in the field of solar energy conversion and environmental remediation including water purification and wastewater treatment. In general, a TiO2 photocatalytic process consists of three major steps, namely, the mass transfer process in solution, the interfacial step, and the photoelectron transport inside the catalyst. This work explores the characterisation of TiO2 photocatalysis using a photoelectrochemical method to focus on each fundamental reaction steps. Each of these steps will be used to gain an accurate understanding of processes and identify possible improvements of the overall performance of TiO2 semiconductor photocatalysts. In this work, nano-sized TiO2 semiconductor photocatalysts were prepared by the solgel method, and immobilised onto a conducting ITO glass substrate to form a photoanode. Photocatalytic studies utilising immobilised TiO2 thin films have many advantages over the suspension/slurry system, including the elimination of the separation process. Most importantly however, photocatalysis by immobilised TiO2 photocatalyst can be manipulated by applying an external potential bias to focus on understanding certain aspects of the photocatalytic process (e.g. the rate determining steps).