Abstract

The importance of hydrogen energy has recently been recognized again, especially by the spread of a fuel cell from the viewpoint of an environmental issue. However, hydrogen is industrially produced by steam reforming of hydrocarbons such as methane. Dihydrogen has to be produced from water using a natural energy if one thinks of the environmental issue. Therefore, water splitting using a photocatalyst is a challenging reaction because it is one of the ultimate reactions to solve energy and environmental issues. Water splitting using photocatalysts is not a new theme. Water splitting has been studied in the research fields of catalysis, electrochemistry, photochemistry, organic and inorganic chemistry, etc. for about 30 years since the Honda–Fujishima effect was reported using a TiO2 semiconductor electrode [1]