Morphology, microstructure, and electrocatalylic properties of RuO2-SnO2 thin films

The electrochemical devices based on conductive RuO2 stabilized by ceramic oxides are the most employed in chlorine-alkali cells. Their efficiency is influenced by many variables, among which the chemical nature of the stabil izer oxide plays a considerable role. In this paper, morphology, microstruc ture, and electrocatalytic properties of supported RuO2-SnO2 thin films, pr epared in a wide compositional range, were investigated by X-ray diffractio n (XRD), scanning tunneling microscopy (STM), and cyclic voltammetry (CV). X-ray analysis indicates an immiscibility zone for the two oxides approxima tely in the range 20-70 atom % of Sn nominal amounts. In both solubility re gions, a tetragonal phase (rutile-type) is formed. Peak profile analysis in dicates a nonequiaxial crystal growth and shows that in solid solutions whe re RuO2 is the major component larger crystallites (about 100-160 Angstrom) are formed than in those where SnO2 is the major component (about 30 Angst rom). STM characterization reveals a rough surface with a complex microstru cture: very large agglomerates, which seems to be made up of a large number of smaller units with sizes of the same order of magnitude found by XRD. O nly in the sample with 70 atom % of Sn (nominal amounts) there exists regio ns where the small units are clearly visible as distinct particles. The CV analysis shows that the highest electrocatalytic activity is exhibited by t he latter sample, which has the highest possible content of RuO2 before it forms a solid solution in SnO2 and where particles tend not to form aggrega tes. (C) 1999 The Electrochemical Society. S0013-4651(97)12-051-1. All righ ts reserved.