A study of the charge propagation in nanoparticles of Fe₂O₃ core-cobalt hexacyanoferrate shell by chronoamperometry and electrochemical impedance spectroscopy

Abstract

A composite electrode comprised of graphite, Nujol, and nanoparticles of Fe₂O₃ core–cobalt hexacyanoferrate shell was prepared and the charge transport processes in the bulk of this composite were studied. The electrode/solution interface was assumed as a binary electrolyte whose charge transport occurred between redox sites of the nanoparticles present in the composite and counter cations present in the solution. Using cyclic voltammetry, the diffusion of counter cation in the shell was investigated. Using chronoamperometry, an effective diffusion coefficient and its dependency on the applied potential was obtained. In the Nyquist diagrams, different time constants were appeared with relation to different physical and electrochemical processes. Percolation of electron in the shell of the nanoparticles appeared at very high frequencies and exhibited the feature of a diffusion process with a transmissive boundary condition at interface of core–shell structure/graphite particles. The diffusion coefficients of electron and counter cation and the standard rate constants of each individual electrochemical reaction were obtained.