(An) investigation of the electrochemical reactions at the interfaces between pure Carbon/Lithium intercalated Carbon electrodes and Aqueous/Nonaqueous electrolytes

Abstract

The present work is concerned with the electrochemical reaction at the interfaces between pure carbon/lithium intercalated carbon electrodes and aqueous/ nonaqueous electrolytes. In chapter Ⅲ, the electrochemical reaction at the interface between platinum -dispersed carbon (Pt/C) and aqueous electrolyte has been considered. The oxygen reduction on unwetted and pre-wetted platinum-dispersed carbon electrode was investigated in 1M $H_2SO_4$ solution at room temperature by using ac-impedance spectroscopy in combination with a current-decay transient technique. From the appearance of an inductive arc in Nyquist plots from the unwetted Pt/C electrode specimen, it is suggested that oxygen reduction proceeds via formation of an intermediate state. The a.c. impedance spectra are also obtained from the Pt/C electrode in 85% $H_3PO_4$ solution at 145℃, with and without oxygen and air blowings. In both cases, an inductive arc in the low-frequency range of the Nyquist plots is observed. The change in impedance spectra with pre-wetting treatment of the Pt/C electrode specimen in 1M $H_2SO_4$ solution and the alteration of spectra with oxygen and air blowings in 85% $H_3PO_4$ solution are discussed in terms of the Epelboin model. From the analysis, it is concluded that as depletion of the dissolved oxygen occurs markedly within the narrow pores of the Pt/C electrode, the inductive arc moves towards the capacitive arc in the low-frequency range. The results of current-decay transients strongly suggest the occurrence of depletion of the dissolved oxygen within the narrow pores. The corrosion behaviour of platinum dispersed carbon electrode has been explored in 85% $H_3PO_4$ solution at 145℃ with concurrent blowings of pure nitrogen, oxygen and mixture of oxygen and nitrogen by using Fourier transform infra-red (FTIR) spectroscopy supplemented by ac-impedance spectroscopy. Ac-impedance spectra indicated that the reactivity of $H_2O_2$ towards chemical decomposition increases ...