Electrochemical behaviour of tris(1,10-phenanthroline)ruthenium(II) at a surface modified electrode. Electrocatalytic reduction of dioxygen

Cyclic voltammetry (CV) of [Ru(phen)3]²⁺ (phen = 1,10-phenanthroline) is studied in CH3CN under N2 at a gold electrode whose surface is modified by thiocyanate. Five one-electron ligand reductions are observed on the negative side of normal hydrogen electrode (NHE), which is unprecedented. Using Randles-Sevcik equation, the electrochemical radius of the electrode has been estimated as 0.86 mm (cf. physical radius: 1 mm). When the Au-SCN electrode is dipped in an CH3CN solution of [Ru(phen)3]²⁺ for 2 h, the cation gets adsorbed on the electrode surface. The resulting Au-SCN-Ru(phen)3²⁺ electrode shows two reductions in plain CH3CN under N2. The number of electrons in each step is found to be 2 when Laviron’s equation is applied with a transfer coefficient α of 0.5. Ferrocene at the Au-SCN-Ru(phen)3²⁺ electrode in CH3CN shows a one-electron oxidation at 0.681 V vs NHE.