Water Splitting by Photocatalysts
Here are two old-fashioned ways to get hydrogen; reforming of fossil fuels(96%) and electrolysis of water (4%). The former is not eco-friendly due to the carbon dioxide coming from the process, and the letter is inefficient because it costs too much to use electric energy. Thus, there are a lot of researches for producing hydrogen energy with eco-friendly and efficient ways by utilizing infinite solar energy. At present, the most ideal way to force solar energy into a source of hydr-ogen energy is photochemical reaction where light absorbable photocatalyst decomposes water into hydrogen and oxygen. This method can be called as the most ideal process to make hydrogen because it uses water (which is abundant in earth) and sunlight (that is most ultimate energy source); furthermore, by-product oxygen is quite beneficial material.
There have been many studies to develop diverse photocatalysts since the fact that TiO2 single crystal electrode can decompose water under light irradiation was reported in 1972. But, there is a serious limit that hydrogen production can be done only in ultraviolet region because most photocatlysts have big more than 3eV- bandgap energy. To effectively harvest solar energy, we need photocatalysts showing activity in the visible region(400nm~700nm; 1.77~3.1eV) for splitting water; because ultraviolet region only occupies 5% of whole solar spectrum. Therefore, there are a lot of researchers who spur developing visible light photocatalysts.
Our group synthesized perovskite-structure material, and it displayed outstanding quantum yield comparing with preexisting photocatalysts. And recently, we developed the oxide photocatalyst showing STH(solar to hydrogen) 3% with support by 21st Century Frontier Center. We have been conducting various researches such as cation(anion) substitution method, intercalation to make visible light photocatalysts for hydrogen production, and now we are focusing on making nano-composite oxide photocatalysts and composite photocatalysts.