Microwave reflectance studies of photoelectrochemical kinetics at semiconductor electrodes. 3. Photolectrochemical reduction of Ru(NH3)(6)(3+) at p-Si

The reduction of Ru(NH3)(6)(3+) at illuminated p-Si in ammonium fluoride solutions was studied by a light modulated microwave reflectivity method. Ru(NH3)(6)(3+) was chosen as an example of a one electron outer sphere redox system that is expected to exhibit facile electron transfer kinetics. The results of the microwave measurements show that the transfer of photogenerated electrons to Ru(NH3)(6)(3+) at an illuminated p-Si electrode is very slow compared to an order of magnitude estimate for outer sphere electron transfer. It is concluded that the reduction of Ru(NH3)(6)(3+) does not involve direct electron transfer from the conduction band but is instead mediated by photogenerated hydrogen states.