Covalent immobilization of molecular complexes on metal-organic frameworks towards robust and highly efficient heterogeneous water oxidation catalysts

The major challenges to practical implementation of efficient noble metal based molecular water oxidation catalysts are their stability and recycle ability. Herein, noble metal Ru based molecular water oxidation catalysts were covalently anchored in MOFs through "amide bond" as bridges, which leads to the formation of highefficiency and robust heterogeneous catalysts for water oxidation reaction. We show that the efficiency for CeIV-driven water oxidation was significantly enhanced by 120 times when the Ru molecules were immobilized on the frameworks of MIL-101(Cr). The relationship between recycle stability and the structure of the Ru complexes covalently anchored in MOFs was carefully studied by recycle tests and various characterization methods. [Ru(terpy)(pic)2(H2O)]2+ was directly certified as real catalytic species instead of the original complex [Ru(terpy)(pic)2Cl]+ by the X-ray absorption spectroscopy and control experiments. The synthetic method of hybrid catalysts offers a good strategy for enhancing water oxidation activity and stability of molecular catalysts.