Impedance Spectroscopy

Electrochemical Impedance Spectroscopy (EIS) is a powerful technique which, in principle, allows identification and characterization of the different processes governing electrochemical systems. Our group has emphasized a comprehensive approach in which experimental design, error analysis, and first-principles models are used to obtain a fundamental understanding of the system under study.

PEM Fuel Cells

Polymer-Electrolyte-Membrane (PEM) fuel cells represent an attractive alternative energy source for transportation and local power generation. Impedance spectroscopy is often applied to PEM fuel cells, but the electrical circuit analogues commonly used to interpret data do not yield unambiguous interpretations of the process. The object of this work is to explore the use of impedance measurements for fuel cells through use of interpretation models that account for the mechanisms of proposed reactions. The measurement model error analysis approach developed in our group was used to show that low-frequency inductive loops, often neglected, contain information relevant to the fuel cell operation. Interpretation models were developed to show that these loops can be attributed to reactions, such as peroxide formation and Pt oxidation, which act to degrade fuel cell performance.   

Influence of Surface Heterogeneity

One of the most pressing issues in interpretation of impedance spectra is associated with the influence of surface heterogeneity on the impedance response. To address this problem, models have been developed which account for the influence of nonuniform current and potential distributions on the impedance response of a disk electrode. The calculations included predictions for the local impedance response. These model results have been verified by experiments performed in our lab and by collaborators in France. The simulations and experiments allow interpretation of local impedance measurements which provide a unique, in-situ, and perhaps under-utilized capability to explore heterogeneities on an electrode surface.