Effect of voltage treatment on modulation frequency dependence of the photoacoustic and photoelectrochemical current spectra of highly porous, polycrystalline TiO2 electrodes

We report the effect of voltage on a concentrated KCl electrolyte applied t o a highly porous TiO2 electrode during its final preparation process on th e photoelectrochemical current (PEC) spectra. Optical absorption measuremen ts were monitored by a photoacoustic (PA) method. The PA spectrum of the Ti O2 electrode with the voltage treatment is similar to that without the trea tment above the band-gap region. Below the band-gap region, the intensities of the PA spectrum of the TiO2 electrode with the voltage treatment are hi gher than those without the treatment, suggesting an increase of carrier co ncentration by the voltage treatment. The PEC spectra without the voltage t reatment show a monotonic increase with the photon energy above the band-ga p region. The PEC intensity with the voltage treatment increases rapidly im mediately above the band-gap region and shows saturated values. The PEC int ensity of the TiO2 electrode with the voltage treatment is approximately tw ice that without the treatment above the band-gap region. The increase of t he PEC intensity implies an increase of carrier concentration due to partia lly reduced Ti ions. The modulation frequency dependence of the PEC intensi ty of TiO2 electrodes with and without the voltage treatment shows two type s of exponential decay. The decay rate in the TiO2 electrode with the volta ge treatment is slower than that without the treatment below the modulation frequency of 100 Hz. The decay rate with the voltage treatment agrees with that without the treatment above the modulation frequency of 100 Hz.