A research group led by Associate Professor Kazuhiko Maeda of Tokyo Institute of Technology, in collaboration with Kyoto University, discovered that a composite material consisting of titanium oxide and cobalt hydroxide functions as an optical electrode that decomposes water under visible light irradiation.It is expected to be applied not only to the production of hydrolyzed hydrogen but also to the photoreduction of carbon dioxide, which is a causative agent of global warming.
The development of optical electrodes that decompose water into hydrogen and oxygen is an important issue from the perspective of realizing "artificial photosynthesis" that converts visible light, which is abundant in sunlight, into chemical energy.Since certain metal oxides such as titanium oxide are relatively easy to synthesize and chemically stable, they have been widely studied as photoelectrode materials for water splitting.However, most of them have a large band gap (energy difference between the conduction band and the valence band), so there is a big problem that only ultraviolet light can be absorbed.
Associate Professor Maeda and his colleagues discovered that an electrode in which cobalt hydroxide is deposited on a titanium oxide thin film laminated on transparent conductive glass becomes a new optical electrode that decomposes water under visible light irradiation.It was found that the same function could not be obtained with titanium oxide or cobalt hydroxide alone, and the visible light absorption capacity generated by the combination of both was the origin of the function expression.
This is the first example of the difficult-to-realize visible light water decomposition using only common materials such as titanium oxide and cobalt hydroxide.Furthermore, this composite optical electrode also has the feature that it can be manufactured by a simple and low-cost method.
In the future, performance improvement is expected by optimizing the optical electrode structure and electrolytic conditions and examining combinations of similar substances.In addition, the composite optical electrode this time is expected to be applied not only to hydrolyzed hydrogen production but also as an optical electrode member for carbon dioxide reduction.
