Abstract
A mononuclear Ru aquo complex, [Ru(C8Otpy)(H2dcbpy)(OH2)]2+ (C8Otpy = 4′-octyloxy-2,2′:6′,2′′-terpyridine, H2dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) was stably adsorbed on a nanoporous TiO2 surface to afford a TiO2 electrode anchoring the complex. The adsorption isothermal of the complex on the TiO2 surface was analyzed by the Langmuir adsorption model to provide a maximum coverage of Гmax = 4.4 × 10−8 mol cm−2 and an adsorption equilibrium constant of Kads = 1.1 × 104 M−1, suggesting that the monolayer of the complex is formed on the TiO2 surface. The cyclic voltammetry measurement of the complex on the TiO2 surface suggested the diffusion-controlled charge transport via electron hopping between the complexes through the TiO2 layer. Pourbaix diagram showed that the complex undergoes a non-H+-coupled 1e- redox reaction of a RuIIOH/RuIIIOH pair of the complex on the TiO2 electrode due to pH buffering ability of the TiO2 surface in a range of pH 5−11. Bulk electrolysis at 1.7 V vs Ag/AgCl using the complex-anchoring TiO2 electrode provided a high and steady catalytic current density of 0.39 mA cm−2 with 83 % Faradaic efficiency for O2 evolution during 1 h electrolysis. However, we presume that the complex is transformed to RuOx nanoparticles on the TiO2 electrode during the electrocatalysis, on the basis of our earlier report on the complex / mesoporous ITO electrode system (Dalton Trans., 2020, 49, 1416−1423.). The RuOH/TiO2 electrode is the efficient anode for water oxidation under the acidic conditions, irrespective of the molecular catalyst of RuOH and the alternative catalysts formed via its oxidative transformation.
Published Version
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More From: Journal of Photochemistry & Photobiology, A: Chemistry
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