High-valent ruthenium(IV)-oxo complex stabilized mesoporous carbon (graphitized)/nafion modified electrocatalyst for methanol oxidation reaction in neutral pH

Abstract

Abstract Owing to its importance in the fuel cell, biofuel and bioinorganic chemistry, since 1981, there has been an immense interest in the development of surface-confined ruthenium-oxo complex and to utilize it as a model bio-mimicking system for oxidation of water and alcohol reactions. In this connection, ruthenium-oxo complex has been attached on solid-surfaces by various chemical approaches. Indeed, the preparation of stable and fouling-free surface-confined ruthenium-complex system is a challenging task. Herein, we report a new methodology based on a modification of [Ru(tpy)(DMSO)Cl2]-Nafion (Nf) precursor, wherein, tpy = 2,2′:6′,2″-terpyridine ligand, system on a graphitized mesoporous carbon (GMC) modified electrode followed by electrochemical treatment for in-situ conversion to a high-valent ruthenium oxo complex electrode, designated as GCE/GMC@[(tpy)RuIV/III=O]-Nf, in pH 7 phosphate buffer solution. It showed a stable and well-defined redox peak at a standard electrode potential, Eo’ = 0.780 V vs Ag/AgCl with a surface-excess value, 5.5 × 10−9 mol.cm−2. Some of the kinetic parameters such as transfer coefficient, α and heterogeneous electron-transfer rate constant, ks values were evaluated as 0.54 and 2.43 s−1 respectively for the redox couple. Collective physicochemical characterizations of the surface-confined system by TEM, Raman, UV–Vis and FTIR spectroscopic techniques and ESI-MS analysis, it has been revealed that [RuIII(tpy)(DMSO)(Cl)(OH)]+ complex is surface-confined on the electrode via π-π interaction, pore-encapsulation, and ionic interaction and further transformed to [(tpy)(DMSO)RuIVO]2+ like complex at an applied bias potential, 0.8 V vs Ag/AgCl. This new surface-confined electrode showed high efficient and enzyme-free electrocatalytic oxidation of methanol with a current sensitivity of 39 μA mM−1 in a neutral pH solution.