RBS and RNA Study of RuO2-SnO2-TiO2 film electrodes

In this work compositional features of film electrodes based on ruthenium, tin and titanium dioxide ternary mixtures have been studied by Rutherford backscattering spectrometry (RBS) and nuclear reaction analysis (NRA). These results have been correlated with their electrochemical properties. The RBS analysis confirmed the nominal concentration. The amount of carbon, found by 12C (d,p)13C nuclear reaction, was larger than 1E17 mol cm-2 in all samples. It has also been found that the amount of residual carbon increases with increasing the titanium concentration. The amount of residual carbon in two 30:70 and 50:50 RuO2-SnO2 binary mixtures is with good approximation the same (about 1E17 atoms cm-2). In this respect, both these oxides exhibit the same behavior, which can have important implications in surface texture and microstructure of the oxide film. On the basis of literature data, from voltammetric charges an estimate of the effective roughness factor of the electrode films was attempted. A roughness factor of about 70-80 was found, independent from the titanium dioxide concentration. In TiO2-containing binary electrode films, like RuO2-TiO2 and IrO2-TiO2, the behavior was quite different. roughness factors around 150-400 being generally estimated. As a complement to CV data, a series of experiments of deuterium exchange was carried out on the electrode films, after polarization at different potentials, in 1 N D2SO4/D2O solutions. The 2H(d,p)3H nuclear reaction was used to follow the changes of uptaken D+. After a ten minutes polarization at a potential of 0.10 V (vs. SCE) values of uptaken D+ of the order of 1E15 could be measured. Almost one order of magnitude larger values have been measured for the above mentioned binary systems. This result can be taken as a support to the CV evidence, indicating low roughness factors for the two series of three-component films. The uptaken D+ amount normalized to the Ru+Sn amount was found to be independent, as well as the roughness factor, from the titanium concentration in the electrode film. Polarization of the electrodes at 0.10 V for twenty min. more, did not result in a significant increase of the deuterium concentration. The electrode film thickness did not affect the amount of uptaken deuterium either. The set of CV and D+ exchange data indicate that, possibly, the presence of tin dioxide in the mixture facilitates dissolution of RuO2 and TiO2, limiting segregation phenomena. Independent microstructural data obtained by the present authors on the SnO2-TiO2 system, indicated, in fact, complete miscibility across all the phase diagram.