Spectroelectrochemical analysis of TiO2 electronic states - Implications for the photocatalytic activity of anatase and rutile

The information on the electronic structure of nano- and microstructured semiconductors is crucial for their applications in photovoltaics, optoelectronics and photocatalysis. The distribution of intra-bandgap electronic states is one of the most relevant parameters which may be tuned in order to provide desired properties of a photoactive material. We propose the use of a modified spectroelectrochemical method for the characterisation of vacant electronic states distributed close to the edge of the titanium dioxide conduction band. These additional levels localized within the bandgap were semi-quantitatively characterized for several samples made of different polymorphs (or their blends) of TiO2. The applicability of the method for the determination of deep and shallow electron traps was confirmed. A quantitative analysis of the latter was also conducted for the selected samples. The presented approach provides also the information on the stability of electronic states, which is crucial for numerous practical applications.