(631c) A Novel Ac Impedance Model for Electrochemical Devices

AC impedance is a powerful non-destructive technique and is used to capture the transport and kinetic limitations in an electrochemical system of interest. AC impedance involves subjecting the system of interest to an alternating signal (e.g., potential) of small magnitude and observing the way in which the electrochemical system responds at steady state (long duration of time). Electrochemical models based on transport phenomena, material/energy balance, and porous electrode theory is used to simulate AC impedance of secondary batteries and fuel cells.

Typically, numerical methods are used to solve the governing equations, since, there is the need to solve systems of coupled partial differential equations in multiple regions simultaneously. The need for a closed form solution arises when one needs to estimate all the competing transport and reaction mechanisms efficiently (parameter estimation). We propose a novel symbolic solution methodology to obtain analytical and symbolic solutions for AC impedance response of electrochemical systems and use these solutions to better understand the system by extracting transport and kinetic parameters.

The advantages and disadvantages of the proposed method in simulating the AC impedance response of electrochemical power sources will be discussed. This work is being funded by the National Science Foundation (CTS – 0609914).