Surface-state photoresponse of the TiO2-electrolyte interface in the near-infrared region

New broad photocurrent peaks, hitherto not reported, when near-infrared photons ($h\nu <1.44\mathrm{}$ eV) are incident at the Ti${\mathrm{O}}_2$-electrolyte interface, are observed at 1000 and 1300 nm. The intensity of these photo-current peaks is largely influenced by the Ti${\mathrm{O}}_2$ bulk optical absorption attributed to defect levels with corresponding 1000- and 1300-nm peak energies. Furthermore, the photocurrent peak energies are not dependent upon the surface condition of Ti${\mathrm{O}}_2$ bulk or the $p\mathrm{H}$ of the supporting electrolyte. A bulk model is proposed to explain these photocurrent peaks.