Analysis of the regeneration behavior of high temperature polymer electrolyte membrane fuel cells after hydrogen starvation

Abstract

Two high temperature polymer exchange membrane fuel cells (HT-PEM FCs) were operated under repeated starvation/regeneration steps for 550 min (DPS-1) and 12 days (DPS-2). Concerning the investigation of the irreversible degradation under fuel (H2) starvation the focus was put on the electrochemical characteristics during regeneration, since during this step the system operates under normal conditions. Electrochemical impedance spectroscopy (EIS) and distribution of relaxation times (DRT) analysis were used as electrochemical characterization methods. DRT analysis of selected impedance spectra during regeneration steps for the first seven days revealed an intensity increase of the charge transfer kinetics of the cathode (ca. 10 Hz) and the anode (ca. 100 Hz). From day 3 on, an additional peak at 300-800 Hz appeared likely pointing to the formation of surface oxides at the anode side. The EIS and DRT results were verified with Focused Ion Beam-Scanning Electron Microscopy (FIB-SEM), Microcomputed Tomography (µ-CT) and Transmission Electron Microscopy (TEM). While TEM indicated advanced Pt particle agglomeration pointing to carbon corrosion, µ-CT measurements showed an increase of void volume fraction and a decrease of the tortuosity value. The combined results show that the anode gas outlet region of the FC is more degraded than the inlet region.