Oxygen Evolution by Means of Water Oxidation Catalyzed by Mononuclear Ruthenium–Ammine Complexes

Abstract

Abstract Water oxidation was achieved catalytically by the use of mononuclear ruthenium–ammine complexes and using Ce(IV) as an oxidant. Cyclic voltammetric studies of the mononuclear ruthenium–ammine complexes [Ru(NH3)5Cl]2+ and [Ru(NH3)5(H2O)]3+, have been carried out using Basal Plane Pyrolytic Graphite (BPG) coated with poly(p-styrenesulfonate), Nafion, or Kaolin clay. The electrochemical properties of these ruthenium–ammine complexes show that they can be used as two-electron oxidants for water oxidation. It has also been found that these complexes oxidize water to evolve oxygen in the presence of excess Ce(IV) under homogeneous as well as heterogeneous conditions. The oxygen evolution by means of water oxidation was confirmed by using the H218O isotope in the reaction medium. The water oxidation process was found to be dependent on the ionic strength of the medium. Higher acidic conditions gave higher O2 yields. Heterogeneous catalysis with the Ru complex adsorbed in Kaolin clay was as effective as the homogeneous one. The water oxidation reaction catalyzed by ruthenium–ammine complexes was also discussed.