Assessing cell polarity reversal degradation phenomena in PEM fuel cells by electrochemical impedance spectroscopy

• Published in: International journal of hydrogen energy 2013-06, Vol.38 (18), p.7684-7696
• Main Authors: Travassos, M.A., Lopes, Vitor V., Silva, R.A., Novais, A.Q., Rangel, C.M.
• Format: Article
• Language: English
• Subjects: Alternative fuels. Production and utilization; Applied sciences; Carbon; Catalyst loss; Degradation; Degradation mechanisms; Distribution of relaxation times; Electrochemical impedance spectroscopy; Electrodes; Energy; Equivalent circuits; Exact sciences and technology; Fuel cells; Fuel starvation; Fuels; Hydrogen; Membranes; PEM fuel cells; Polarity
• ISSN: 0360-3199; 1879-3487
• DOI: 10.1016/j.ijhydene.2013.01.132

Electrochemical impedance spectroscopy (EIS) is identified as one of the most promising in-situ diagnostics tools available for assessing fuel cell ageing and degradation. In this work, the degradation phenomena caused by cell polarity reversal due to fuel starvation of an open cathode 16 membrane electrode assembly (MEA) – low power (PEM) fuel cell (15 W nominal power) – is reported using EIS as a base technique. Measuring the potential of individual cells, while the fuel cell is on load, was found instrumental in assessing the “state of health” of cells at fixed current. Location of affected cells, those farthest away from hydrogen entry in the stack, was revealed by very low or even negative potential values. EIS spectra were taken at selected break-in periods during fuel cell functioning. The analysis of impedance data was made using an a priori equivalent circuit describing the transfer function of the system in question – equivalent circuit elements were evaluated by a complex non-linear least square (CNLS) fitting algorithm, and by calculating and analyzing the corresponding distribution of relaxation times (DRT). Results and interpretation of cell polarity reversal due to hydrogen starvation were complemented with ex-situ MEA cross section analysis, using scanning electron microscopy. Electrode thickness reduction and delamination of catalyst layers were observed as a result of reactions taking place during hydrogen starvation. Carbon corrosion and membrane degradation by fluoride depletion are discussed. ► Fuel starvation was assessed by EIS using the distribution of relaxation times analysis. ► Electrode thickness reduction and delamination of anode catalyst layers were detected. ► Carbon corrosion and membrane degradation by fluoride depletion were also observed.