Chinese Journal of Catalysis ›› 2013, Vol. 34 ›› Issue (8): 1489-1495.DOI: 10.1016/S1872-2067(12)60600-7

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Chemical and photocatalytic water oxidation by mononuclear Ru catalysts

Yi Jianga, Fei Lia, Fang Huanga, Biaobiao Zhanga, Licheng Suna,b   

  1. a State Key Laboratory of Fine Chemicals, Faculty of Chemical, Environmental and Biological Science and Technology, Dalian University of Technology, Dalian 116024, Liaoning, China;
    b Department of Chemistry, School of Chemical Science and Engineering, KTH Royal Institute of Technology, Stockholm 10044, Sweden
  • Received:2013-03-22 Revised:2013-04-10 Online:2013-08-16 Published:2013-07-30
  • Supported by:

    This work was supported by the National Basic Research Program of China (973 Program, 2009CB220009), the National Natural Science Foundation of China (21106015, 21120102036, and 20923006), the Research Fund for the Doctoral Program of Higher Education of China (20110041120005), and the Swedish Energy Agency and K&A Wallenberg Foundation.

Abstract: Four mononuclear Ru complexes with different substituents on the para position of the pyridine ligand of Ru(bda)(pic)2 (H2bda=2,2'-bipyridine-6,6'-dicarboxylic acid; pic=picoline) were synthesized and characterized by 1H nuclear magnetic resonance or X-ray crystallography. The electrochemical properties of this series of compounds in acidic and neutral conditions were studied by cyclic voltammetry. Their catalytic activity towards water oxidation was investigated using a chemical oxidant ([Ce(NH4)2(NO3)6] (CeIV) in acidic solution, or driven by visible light in a three-component system containing a photosensitizer ([Ru(bpy)3]2+) and an electron acceptor (S2O82-). For the chemical water oxidation, complex 1 was found to be the most effective, exhibiting a turnover number (TON) of up to 4000. The pyridine substituent at the 4-position in 1 may be protonated giving an intensive electron-withdrawing effect. Complex 2 bears the most electron-withdrawing trifluoromethyl group under neutral conditions and showed the highest photocatalytic activity with a TON of 270 over 2 h. It was concluded that the more electron-withdrawing substituents led to higher activity towards oxygen evolution for this type of Ru catalysts in the oxidation of water.

Key words: Water splitting, Water oxidation, Ruthenium complex, Electron-withdrawing effect, Photocatalysis