Microstructural characterization and electrochemical properties of RuO2 thin film electrodes prepared by reactive radio-frequency magnetron sputtering

Ruthenium dioxide films were prepared by radio-frequency magnetron sputtering onto Si and Ti substrates. Films of different thicknesses (100-500 nm) were synthesized at substrate temperatures of 40, 350, and 450 degreesC. Their composition has been studied by Rutherford backscattering spectrometry, elastic recoil detection, and ion beam nuclear reaction analysis. Scanning electron microscopy and wide-angle X-ray scattering have been used for studying the surface texture of the samples and for their microstructural characterization, respectively. The electrochemical characterization by cyclic voltammetry has shown that, despite the high physical density of the films, compared with that obtained by the thermochemical methods, they exhibit large charge-storage capacities. For the materials synthesized at 350-450 degreesC, an explanation of these results has been sought in specific features of the RuO2 rutile-type cell and columnar texture of the oxide film. The much higher capacity of the films synthesized at 40 degreesC would be rather due to a poor sintering of the oxide phase. Study of the chlorine evolution reaction in the samples prepared at 350 and 450 degreesC points to a Volmer-Tafel mechanism, with a chemical desorption rate-determining step, and significant radical intermediate coverage. Films deposited at 40 degreesC exhibited an unsatisfactory wear resistance under the anodic polarization required for the chlorine evolution reaction investigation.