Preparation of Ru and Ru-alloy particles by electrochemical techniques

M.M.E. DUARTE; J.M. SIEBEN; C.E. MAYER

Ruthenium: Properties, Production and Applications

Nova Science Publishers Inc.

Lugar: New York; Año: 2011; p. 421 - 455

One of the most significant applications of ruthenium involves the production of catalysts composed mainly by alloys with other metals as well as ruthenium oxides. For certain applications micro and nano particles dispersed over a substrate with specific characteristics are required. The development and the increasing expansion of fuel cells technologies as a future power source forvehicles, small electronic devices and residential generators has increased extraordinarily the demand of ruthenium to prepare Pt-Ru anodes for hydrogen, methanol and recently ethanol oxidation, and RuOx cathodes for oxygen reduction. These electrodes are composed mainly by dispersed nanoparticles supported on a conductor material as carbon. The characteristics of the support make possible the use of electrochemical techniques to prepare metallic particles with different properties to those obtained by chemical reduction methods. The production of nanoparticles by electrochemical techniques presents severaladvantages such as simple preparation, low cost, high purity, and uniform deposition. Besides, they offer an effective way to deposit the catalyst selectively at desired locations on the electrode with both ionic and electronic access. The current density or the overpotential is responsible for the number and size of the nanoparticles. The use of organic additives facilitates control of the crystallization process. The procedure generally involves the use of acid-aqueous solutions ofruthenium salts (RuCl3, K2RuCl5, Ru(NO)(OH)3, RuNOCl3, Ru(NO)x(NO3)y, etc.) with other metal salts (H2PtCl6, PdCl2, etc.) as well as compounds that modifies metal activity or oxidation state or assists in the formation of colloidal nanoparticles. Therefore the particle characteristics (composition, morphology, size, and inclusive dispersion over the substrate) can be controlled by the chemical composition of aqueous solution.The electrochemical techniques applied to prepare the catalysts include pulse current, direct current, constant potential and multiple galvanostatic and potentiostatic pulses, cyclic voltammetry, coulostatic deposition, etc.. The central idea of this review is to evaluate diverse characteristics ofdispersed Ru-Metal alloys and ruthenium oxides prepared by electrodeposition including composition, stability, structural features, and mechanistic aspects as well as their application in fuel cells technology.