The photoelectrolysis of water in cells with SrTiO3 anodes has been confirmed. The maximum external quantum efficiency at zero bias voltage is 10% (at hν=3.8 eV), about an order of magnitude higher than the maximum value obtained with anodes of TiO2, the only other material so far known to catalyze photoelectrolysis. In agreement with the energy-level model proposed previously, the efficiency is increased because the band bending at the anode surface is about 0.2 eV larger for SrTiO3 than for TiO2, as a result of the smaller electron affinity of SrTiO3.

No abstract

Electronic surface states play a significant role in charge transfer between the electrolyte and the n-type SrTiO2 semiconducting electrodes used in the photoelectrolysis of water. To clarify the role of these states, we have measured the wavelength response of the photovoltage developed between the SrTiO3 surface and a vibrating Au reference electrode, both in vacuum and in a water vapor ambient. When the SrTiO3 is exposed to sub-band-gap radiation, the amplitude and sign of the photovoltage vary with photon energy. Significant changes in the spectrum result from the introduction of water vapor. The energy-dependent structure is interpreted in terms of photon-induced electronic transitions between the states near the surface and conduction or valence band states.