Behaviour of the adsorbed chloride intermediate in electrocatalysis of anodic chlorine evolution at oxide film surfaces at platinum and ruthenium.
|Title:||Behaviour of the adsorbed chloride intermediate in electrocatalysis of anodic chlorine evolution at oxide film surfaces at platinum and ruthenium.|
|Abstract:||In this thesis, the investigation of the mechanism of chlorine evolution reaction at (i) both freshly reduced and pre-oxidized Pt electrodes; (ii) RuO$\sb2$-TiO$\sb2$ electrodes (DSA); (iii) other noble metals such as Pd, Ir, Ru and Rh by means of computer controlled anodic polarization, potential-relaxation transients and a.c. impedance measurements, will be presented. As described in Chapter V, the influence of co-deposited OH and O species in the surface oxidation process on the extent of chemisorption of the Cl$\sp-$ intermediate in the Cl$\sb2$ evolution reaction has been carefully examined. Experimental results reveal that the reaction rate at reduced Pt surfaces is much greater than that at pre-oxidized ones. This is because the oxide species have a significant effect in blocking the Cl$\sb2$ evolution kinetics. The detectable surface adsorption pseudocapacitance, which is associated with the "overpotential deposited" Cl$\sp-$ intermediate, at freshly reduced Pt and oxide free Pt surfaces in non-aqueous trifluoroacetic acid (TFA) medium supports this conclusion. In Chapter VI, some exploratory experiments at other noble metal (e.g., Pd, Ir, Ru, and Rh) electrodes in non-aqueous TFA solution have shown very interesting interfacial capacitance information, which must be interpreted probably in terms of more than one adsorbed reaction intermediate being present. In Chapter VII, a possible mechanism of recombination kinetically control has been proposed for the Cl$\sb2$ evolution reaction at RuO$\sb2$-TiO$\sb2$ electrodes, based on the observations of their steady-state behaviour, and electrochemical data from potential relaxation and a.c. impedance measurements. Local supersaturation of Cl$\sb2$ in the microstructure of the oxide film appears to make a contribution to the pseudocapacitance behaviour. Some of the results in this work have been published or in press, as listed below: (1) "Surface electrochemistry of the anodic chlorine evolution reaction at Pt influence of co-deposition of the Cl$\sp-$ intermediate", P. Gu and B. E. Conway, J. Chem. Soc. Farada Trans. 86(6) (1990) 923. (2) "Behaviour of the adsorbed Cl$\sp-$ intermediate in anodic chlorine evolution at thin-film RuO$\sb2$ surfaces", P. Gu and B. E. Conway, J. Appl. Electrochem., in press. (3) "Evaluation of Cl$\sp-$ adsorption in anodic chlorine evolution at Pt by means of a.c. impedance and potential relaxation experiments: role of the state of surface oxidation", P. Gu and B. E. Conway, J. Chem. Soc. Faraday Trans., in press.|
|Collection||Thèses, 1910 - 2010 // Theses, 1910 - 2010|