Ruthenium electrodeposition from aqueous solution at high cathodic overpotential

Electrodeposition of Ru from aqueous solution was undertaken at potentials of between -4 and -5 V versus Ag/AgCl. At these potentials vigorous hydrogen bubbling off the surface accounted for over 95% of the current passed, imposing hydrodynamic conditions that enabled the creation of high surface area structures, including branched, dendritic morphologies of electrodeposited Ru for the first time. An initial pulse sequence to seed the substrate with Ru was necessary to give a uniform distribution of Ruthenium on the macroscale and allow reproducible surfaces to be deposited. Concentrations of HClO4 and Ru in the electrolyte were both critical to the morphology, with branching, higher surface area growth favored by a lower Ru concentration (15 mM). Roughness factors above 400, and specific surface areas of up to 18.8 m(2)/g of Ru were obtained. Fern-like deposits formed by dendritic growth were observed at the substrate surface, followed by compact growth as the deposit grew away from the substrate. Surface analysis by XPS and voltammetry confirmed that the Ru was deposited in the 0 oxidation state. Annealing of the surface at temperatures from 150 degrees C to 400 degrees C led to the formation of stable ruthenium oxides with potential applications in electrocatalysis.