A Molecular-Based Artificial Photosynthetic System Driving Efficient Overall Solar Water Splitting by One-Step Visible-Light Excitation

In this decade, various attempts have been made to develop a molecular-based artificial photosynthetic system for overall solar water splitting by using various functional molecules, such as a photosensitizer (PS), a water oxidation catalyst (WOC), and a water reduction catalyst (WRC). Nevertheless, the report on such an artificial photosynthetic system that can efficiently promote overall solar water splitting is still extremely rare. In this study, a molecular-based photoelectrochemical cell (MPEC) has been constructed by using the mesoporous TiO2 photoanode chemisorbed with both a polypyridyl ruthenium PS and WOC, and the mesoporous TiO2 dark cathode chemisorbed with a platinum porphyrin WRC. Here we demonstrate that our MPEC is capable of splitting water into H2 and O2 in a 2:1 molar ratio with an almost quantitative Faradaic efficiency upon visible light irradiation only to the photoanode. The solar-to-hydrogen conversion efficiency achieved by our MPEC (0.06%) is found to be the highest value among the fully artificial MPECs reported thus far even though our MPEC still needs a small applied potential. This study reveals that our MPEC is an unprecedented fully artificial photosynthetic system enabling efficient overall solar water splitting via one-step photoexcitation mechanism.