Tokyo Institute of Technology, Japan
Title: Design of metal-to-metal charge transfer chromophores for visible light activation of oxygen evolving Mn oxide catalysts in a polymer film
Biography: Akira Yamaguchi
Developing effective solar to energy conversion system is highly demanding for sustainable society, and one of the challenges is the management of the charge transfer between photo-absorption center and catalysts. In this work, to construct photo-responsive unidirectional charge transfer units for the activation of oxygen-evolving manganese oxide (MnOx) catalyst, metal-oxide nanoclusters consisting of cerium (CeIII) or cobalt (CoII) ions and Keggin-type polyoxotungstate (PW12O403-) were synthesized in a polymer matrix as visible-light-absorbing chromophores. The utilization of the polymer matrix enabled the molecularly-dispersed PW12O403- states and was advantageous to achieve product separable energy conversion systems. The reaction of PW12O403- with Ce or Co ions in the polymer matrix generated the new broad absorption tails extending from UV to visible region assignable to metal-to-metal charge transfer (MMCT) transitions of oxo-bridged binuclear WVI–O–CeIII and WVI–O–CoII units. Although visible light irradiation of the polymer membrane having WVI–O–CoII units generated negligible photocurrent, a clear anodic photocurrent response assigned to photo-induced WVI–O–CoII ® WV–O–CoIII transition was observed after the coupling of MnOx catalysts to WVI–O–CoII units. This finding demonstrated that the generation of anodic photocurrent is derived from the activation of MnOx catalyst by the photo-generated CoIII through confined WVI–O–CoII linkages. The system in this work based on POM and polymer, and its synthetic method provide us a novel methodology to develop artificial photosynthetic systems with spatially and energetically-optimized components.