Degradation effects at the methanol inlet, outlet and center region of a stack MEA operated in DMFC

• Published in: Journal of power sources 2011-07, Vol.196 (13), p.5538-5545
• Main Authors: Dixon, D., Wippermann, K., Mergel, J., Schoekel, A., Zils, S., Roth, C.
• Format: Article
• Language: English
• Subjects: Applied sciences; Area-specific; Catalysts; Degradation; Direct energy conversion and energy accumulation; Dissolution; DMFC; Electrical engineering. Electrical power engineering; Electrical power engineering; Electrochemical conversion: primary and secondary batteries, fuel cells; Energy; Energy. Thermal use of fuels; Equipments for energy generation and conversion: thermal, electrical, mechanical energy, etc; Exact sciences and technology; Fuel cells; Inlet; Inlets; Methyl alcohol; Outlet; Outlets; Ru dissolution; Ruthenium; Stack MEA; Stacks; Transmission electron microscopy
• ISSN: 0378-7753; 1873-2755
• DOI: 10.1016/j.jpowsour.2011.02.007

► Structural investigation done on an aged DMFC MEA. ► Three phases of Ru present in the anode catalyst, oxidized, unalloyed and alloyed. ► Anhydrous RuO 2 presence confirmed by XAS at methanol outlet. ► Precipitation of Ru found in the membrane at the anode outlet due to fuel starvation. ► Cross over Ru was found allover cathode in oxidized form. Ru dissolution is one of the key issues in direct methanol fuel cells (DMFC). A used DMFC stack membrane electrode assembly (MEA) was analyzed using different analytical techniques like X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), transmission electron microscopy (TEM) and EDX and different regions probed in the process. Catalyst powder from e.g. like methanol inlet, outlet and center were investigated and compared with the as-received commercial electrocatalyst and the pristine MEA after manufacture. The large oxidized ruthenium fraction in the anode catalyst was found to play a significant role in particle growth and ruthenium dissolution. Crossover ruthenium from the anode side was found to be dispersed everywhere in the cathode in its oxidized form, and thus can have a significant effect on the oxygen reduction activity (ORR). Although with XRD no significant structural changes were observed for the different regions of the MEA, TEM and EDX analysis showed the preferential precipitation of the Ru at the methanol outlet.