Position dependent analysis of membrane electrode assembly degradation of a direct methanol fuel cell via electrochemical impedance spectroscopy

• Published in: Journal of power sources 2013-11, Vol.241, p.127-135
• Main Authors: Hartmann, Peter, Zamel, Nada, Gerteisen, Dietmar
• Format: Article
• Language: English
• Subjects: Applied sciences; Degradation; Direct energy conversion and energy accumulation; DMFC; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Electrochemical impedance spectroscopy; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Spatial influence
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2013.04.041

The performance of a direct methanol fuel cell MEA degraded during an operational period of more than 3000 h in a stack is locally examined using electrochemical impedance spectroscopy. Therefore, after disassembling the MEA is cut into small pieces and analyzed in a 1 cm2 test cell. Using a reference electrode, we were capable of measuring the anode and cathode spectra separately. The spectra of the segments at different positions do not follow a specified trend from methanol inlet to outlet of the stack flow field. The anode spectra were analyzed with an equivalent circuit simulation. The conductance of the charge transfer was found to increase with current density up to a point where a raising limitation process of the complex methanol oxidation dominates, which is not a bottleneck at low current density. Further, an increase of the double layer capacitance with current density was observed. The diffusion resistance was calculated as an effective diffusion coefficient in the order of 10−10 m2 s−1; implying that the diffusion limitation is not the bulk diffusion in the backing layer. Finally, the degree of poisoning of the catalysts by carbon monoxide was measured as a pseudo inductive arc and decreases with increasing current. •Local degradation of a long-term operated DMFC MEA is analyzed.•Anode and cathode impedance are measured by reference electrode.•Anode spectra were analyzed by equivalent circuit modeling.•Degradation is not correlated with the flow field pattern.