ABSTRACT
With semiconductor materials as electrodes, and illuminating with light more energetic than the bandgap of these materials, the electrochemical reduction of carbon dioxide may be achieved at much lower bias potentials than in the "dark" electrochemical reduction, resulting in considerable saving in the input of electrical energy. Using semiconductor electrodes as photoelectrodes, some of the overpotential required for the reduction of carbon dioxide may be gained by the photopotential produced. Unfortunately, most of the semiconductors which have a bandgap overlapping the visible part of the solar spectrum (about 300 to 800 nm), and which could thus be useful for solar energy conversion, are unstable in aqueous electrolytes. The general principles of photoelectrochemistry and photocatalysis at semiconductors were reviewed by Bard, l and their applications to the reduction of carbon dioxide were discussed by Halmann2 and Taniguchi.3
