Precious metal oxides for electrochemical energy converters: Pseudocapacitance and pH dependence of redox processes

The mechanism of charge storage in hydrous platinum metal oxides is considered in more detail with respect to the pH dependence of redox capacitance for applications in double-layer capacitors. fuel cells, and pH sensors. An amorphous RuO(2) electrode is able to work like a pH glass electrode during the titration of hydrochloric acid with sodium hydroxide Solution. It is shown that the proton exchange mechanism at a glass membrane can be reproduced by platinum metal oxide-hydrates bound in a polymer matrix. Hydrous RuO(2), obtained by alkaline precipitation or thermal decomposition from RuCl(3), as well as single crystal RuO(2), were characterized by TOF-SIMS, NMR spectroscopy. and electrochemical techniques. The proton conductivity of hydrous RuO(2) appears to be due to the dissociative adsorption of water and the formation of acidic OH groups in Ru(III, IV) cluster ions. Depending oil the pH of the solution, the electrode potential is determined by the formal hydrogen oxidation or oxygen reduction in ruthenium cluster ions. During aging, the active Ru(III) surface sites are partially oxidized to Ru(IV). (C) 2008 Elsevier B.V. All rights reserved