Ru–bis(pyridine)pyrazolate (bpp)-Based Water-Oxidation Catalysts Anchored on TiO₂: The Importance of the Nature and Position of the Anchoring Group

© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Three distinct functionalisation strategies have been applied to the in,in-[{RuII(trpy)}2(μ-bpp)(H2O)2]3+ (trpy=2,2′:6′,2′′-terpyridine, bpp=bis(pyridine)pyrazolate) water-oxidation catalyst framework to form new derivatives that can adsorb onto titania substrates. Modifications included the addition of sulfonate, carboxylate, and phosphonate anchoring groups to the terpyridine and bis(pyridyl)pyrazolate ligands. The complexes were characterised in solution by using 1D NMR, 2D NMR, and UV/Vis spectroscopic analysis and electrochemical techniques. The complexes were then anchored on TiO2-coated fluorinated tin oxide (FTO) films, and the reactivity of these new materials as water-oxidation catalysts was tested electrochemically through controlled-potential electrolysis (CPE) with oxygen evolution detected by headspace analysis with a Clark electrode. The results obtained highlight the importance of the catalyst orientation with respect to the titania surface in regard to its capacity to catalytically oxidize water to dioxygen. In or out? Ru-bis(2-pyridyl)pyrazole (Hbpp) complexes have been anchored on a TiO2 surface through functionalisation of terpyridine and bis(pyridyl)pyrazolate ligands (see the picture). The nature of the anchoring group and its geometrical design strongly influence the performance of the anode with regard to the electrocatalytic oxidation of water to dioxygen.