Toward Artificial Photosynthesis: Photocatalytic Water Oxidation and CO2 Reduction

Takahiko Kojima
University of Tsukuba
Dec. 1 11:10~11:35


As a strategy to confront energy and environmental problems, artificial photosynthesis has been intensively investigated worldwide including photocatalytic water splitting (O2 and H2 evolution) and CO2 reduction.

We have developed an efficient photocatalytic water oxidation system using a bis(m-hydroxo) dinuclear Co(III) complex as a catalyst in the presence of [RuII(bpy)3]2+ as a photosensitizer and Na2S2O as an oxidant: The complex showed 742 of turnover number and 44% of quantum yield for the water oxidation.1 In the course of O2 evolution, an intramolecular O-O bond formation occurs through a radical coupling mechanism in a putative bis(m-oxyl) Co(III) dimeric intermediate, which should be formed via proton-coupled electron-transfer oxidation of the bis(m-hydroxo) Co(III) dimer.

On the other hand, we have developed a photocatalytic CO2 reduction system with high selectivity in CO production over H2 evolution (> 99%) using a Ni(II) complex having S2N2-type tetradentate ligand, inspired by the active center of carbon monoxide dehydrogenase.2 In the photocatalytic CO2 reduction, the Ni(II) complex acts as a homogeneous catalyst to form a Ni(0) intermediate that undergoes coordination equilibrium with CO2. The CO formation was revealed to proceed in a water-assisted mechanism with showing solvent kinetic isotope effect of water.


  1. T. Ishizuka, A. Watanabe, H. Kotani, D. Hong, K. Satonaka, T. Wada, Y. Shiota, K. Yoshizawa, K. Ohara, K. Yamaguchi, S. Kato, S. Fukuzumi, T. Kojima, Inorg. Chem. 2016, 55, 1154-1164.
  2. D. Hong, Y. Tsukakoshi, H Kotani, T. Ishizuma, T. Kojima, J. Am. Chem. Soc. 2017, 139, 6538-6541.



  • 1988-1991, Ph.D. The University of Tokyo, Japan
  • 1986-1988, M.E. The University of Tokyo, Japan
  • 1982-1986, B.E. The University of Tokyo, Japan


Professional Career

  • 2008-Present, Professor, University of Tsukuba
  • 2005-2008, Associate Professor, Osaka University
  • 1994-2005, Assistant Professor, Kyushu University
  • 1993-1994, Temporary researcher, Department of Chemistry, Kyushu University
  • 1991-1993, Postdoctoral Fellow, University of Minnesota


Academic Activity

  • 2011-Present, Associate Editor; Bulletin of Chemical Society of Japan (CSJ)
  • 2015-Present, Editorial Advisory Board; Inorganic Chemistry (ACS)


Awards and Honors

  • 2015, Award for Referees of KAKENHI (First Stage)
  • 2008, General Education Award, Osaka University