Highly Efficient Hydrogen Formation using Photoexcited Semiconductro Surface

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Solar energy is a very useful energy, and it is used as a source of light and heat, or it is transformed into chemical energy, electric energy and so on. For an energy conversion of light energy, photosynthesis is representive. In natrure, plants can store solar energy in themselves by way of photosynthesis reaction. We have been interested in light-related chemical phenomena. Utilization of light energy to induce chemical reactions is our main concern. The photoelectrochemical approaches are actively pursued for the production of hydrogen, a clean energy source by an artificial photosynthesis system.As the artificial system, we proposed a semiconductor electrode system. The point is that there exists an interface between solid layr of photo-reactive semiconductor and water and photo-induced reaction occurs at the interface. When a semiconductor electrode is in contact with an electrolyte solution, a space charge layr within a thin semiconductor surface region is formed. Then, this electrode receives photons with energy greater than its band gap E_g, electron-hole pairs are generated within the space charge layr.The generated carriers are concerned in the hydrogen or oxygen evolution on the electrode surface depending on types of semiconductor.The possibility of solar photoelectrolysis was demonstrated by us for the first time with a system in which an n-type titanium dioxide (TiO_2) electrode was connected to a platinum black electrode, the former exposed to near-uv light. This research project has achieved to form hydrogen efficiently by using P-type semiconducting diamond electrode under uv light.