Apparent values (Dap) of chemical diffusion coefficients (D) of intercalated species were measured with the potentiostatic intermittent titration technique (PITT) due to the usual approximations of infinitely fast charge-transfer kinetics at the electroactive interface and negligible Ohmic drop effects. A simple expression was derived here that permitted the prediction of the parametric dependence of the diffusion coefficient ratio (Dap/D) upon the ‘key-factor’ (Λ) for insertion/extraction processes. The parameter Λ could either be experimentally determined from electrochemical impedance spectra, or predicted from theoretical expressions of insertion/extraction reaction rate. The measurement error of diffusion coefficient was predicted theoretically due to slow charge-transfer kinetics at the interface, Ohmic drop effects and bulk interactions in the host material. The influence of electrode or particle geometry was also analyzed. In most cases, but not in all cases, a minimum value of apparent diffusion coefficient was observed near the standard potential of insertion material. The measurement error of D became very important in the presence of attractive interactions in host materials, together with slow charge-transfer kinetics at the electroactive interface. Finally, the superposition between spurious behavior of the chemical diffusion coefficient and its dependence on the guest ions interactions was investigated within the framework of Frumkin insertion isotherm.

Apparent Diffusion Coefficient of Intercalated Species Measured with PITT - a Simple Formulation. C.Montella: Electrochimica Acta, 2006, 51[15], 3102-11