Identification of Polarization Losses in High-Temperature PEM Fuel Cells by Distribution of Relaxation Times Analysis

Abstract

In this study, Distribution of Relaxation Times (DRT) analysis is applied for identification of polarization losses in High Temperature Polymer Electrolyte Membrane Fuel Cells (HT-PEMFCs). Electrochemical impedance spectra recorded for different air stoichiometries and current densities are analyzed. While basic impedance analysis broadly recognizes the presence of three features, DRT reveals at least six distinct processes occurring on different time scales. By varying the stoichiometry and current bias, three of those processes are attributed to mass transport and cathodic kinetics. Furthermore, the DRT analysis suggests that the cathode kinetics may involve two different processes, as opposed to a single-feature process that is often assumed. These results have improved our understanding of the loss mechanisms in HT-PEMFCs and provide valuable guidance for fuel cell optimization.