ABSTRACT
Using semiconductor electrodes as photoelectrodes, some of the overpotential required for the reduction of carbon dioxide may be gained by the photopotential produced. Fujishima and Honda^ pioneered in demonstrating the use of an illu minated single crystal n-Ti02 semiconductor electrode for the photolysis of water. In semiconductors under illumination with light of wavelengths shorter than the band-gap, absorption of light quanta causes excitation of electrons from the valence band to the conductance band. With p-type semiconductors, electrons from the conductance band may interact with electron-deficient molecules such as CO2 adsorbed on the semiconductor surface, causing reduction of these molecules. In most photoelectrochemical systems, the major reduction product was HCOOH. With some electrode and mediator combinations, selectivity to CO or methanol was obtained.
