Pulsed laser-induced photoelectrochemistry at polycrystalline and single-crystal semiconductor electrodes

Abstract

Our studies have focused on the production and detection of transient phenomena related to u. v. –visible photoelectrolysis at various types of semiconductor electrodes. For this work we have utilized xenon flash-lamp and pulsed dye-laser sources. We are reporting on two significant aspects of this work: a theoretical/experimental description of the time dependence of pulse photocurrents and experimental studies directed at the detection of transient intermediates in photoelectrolysis processes. Two experimental measurement approaches have been investigated. One of these involves controlled-potential chronoamperometry, utilizing potential steps synchronized with pulsed irradiation for detection of transient photoproducts. The other approach involves photocoulostatic potentiometry, where open-circuit photovoltage excursions are studied with sub-microsecond time resolution. The former approach allows selective monitoring of various potential regions for qualitative identification of transient photoproducts, whereas the latter approach allows much faster time resolution of photo-induced events. These studies were conducted with single-crystal n-TiO2, p-GaP, p-GaAs and polycrystalline n-TiO2. Because of the much lower ohmic resistance, the polycrystalline electrodes allowed the best time resolution for controlled-potential experiments. A discussion of the limitations of time-resolved measurements, as well as the nature and significance of transient photoinduced processes is presented.