THEORY OF THE ELECTROCHEMICAL IMPEDANCE OF MACROHOMOGENEOUS POROUS-ELECTRODES

An equation for the impedance of a macrohomogeneous porous electrode is derived for the general case (finite electrode thickness and resistivities of the solid and liquid phases), and it is shown how to obtain from it the general solution for the transient state. The electrode model is represented by a transmission line equivalent circuit, and the theory is further generalized by including an arbitrary time delay (a hindrance) of the charge transfer process at the pore surface. A reformulation leads to the definition of an appropriate dielectric function. Two hindrance processes are considered, namely control of the charge transfer by finite diffusion and control by both diffusion and formation of a pseudocapacity (ie charge storage) on a molecular scale. The resulting impedance characteristics for selected parameter values are discussed and preliminary results of fitting experimental data with the new theory are presented.