Photocatalytic Semiconductor for Solar Fuel Generation
Department of Physics, Manonmaniam Sundaranar University, Tirunelveli-627012, Tamil Nadu, India.
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Solar Energy is the world’s largest renewable energy resource. As such, the development of artificial photosynthetic systems capable of converting solar energy into stored energy in the bonds of a chemical fuel is attracting extensive interest. Such ‘solar fuels’ have potential applications as transport fuels, chemical feed stocks and as fuels for electricity generation out of daylight hours. The strategies for semiconductor based photocatalytic CO2 reduction are all based on band gap photoexcitation of a semiconductor to generate electron– hole pairs. When light is incident on the semiconductor, electrons located in the valence band (VB) in the semiconductor can be excited by light having energy greater than the band gap of semiconductor, the energy difference between the top of the filled valence band and the bottom of the empty conduction band (CB), resulting in the electrons being promoted from the VB to the CB, simultaneously leaving positively charged holes in the VB. The pair can, if recombination does not happen as fast as separation and transportation, travel to the surface of semiconductor and split water to produce oxygen and hydrogen or reduce CO2 to yield hydrocarbons. To occur in such a system, it is necessary to have a semiconductor with valence and conduction band edges that both match the energetic requirements of these reactions. There has been significant progress towards the development and enhancements in efficiency and stability. In addition to a reduction in cost of such materials will be required to make the production of solar fuels an economically viable technology for wide-spread application.