Investigations of performance degradation and mitigation strategies in direct methanol fuel cells Ji-Yeon Park a,b , M. Aulice Scibioh a , Soo-Kil Kim a , Hyoung-Juhn Kim a , In-Hwan Oh a , Tai Gyu Lee b , Heung Yong Ha a, * a Centre for Fuel Cell Research, Korea Institute of Science and Technology, P.O. Box 131, Cheongryang, Seoul 130-650, South Korea b Department of Chemical Engineering, Yonsei University, Seoul 120-749, South Korea article info Article history: Received 16 July 2008 Received in revised form 22 October 2008 Accepted 23 October 2008 Available online 18 January 2009 Keywords: Direct methanol fuel cell Lifetime operation Performance loss Durability Hydrophobicity Recovery process abstract This paper addresses a gradual performance loss that is encountered in a direct methanol fuel cell (DMFC) when it is subjected to a continuous operation at constant-load conditions for a period of 600 h. To gain insights into the physico-chemical origins of the degradation process, various analytical techniques are employed and characterization of the membrane electrode assembly (MEA) is carried out before and after the lifetime test. The results reveal that the performance degradation of MEA mainly stems from the degradations at the cathode, and this is further confirmed by individual impedance analyses of cathode and anode as well as by the observation on finding increased quantity of methanol exiting from the cathode with increased operational time. Supplement experiments with the cathodes containing either pre-oxidized Pt catalyst or a fractional amount of Ru catalyst offer new clues to understand the deactivation mechanism. The hydrophobicity losses of gas diffu- sion layers are prominent in the outlet regions compared to the inlet regions of the DMFC assembly. Further, a couple of restoration techniques are employed to evaluate perfor- mance recovery. A periodical on–off switching of applied load and an air-break technique are found to be effective to restore the performance loss that occurs during fuel cell operations. ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. 1. Introduction Due to intensive R&D efforts over the last decade, direct methanol fuel cell (DMFC) technology is in a decisive phase. DMFC remains attractive for portable power applications due to its simple system configuration [1–3]. A key to commercial implementation of DMFC is the demonstration of a reliable long life. Presently, the performance of state-of-the-art DMFC systems can compete favorably with hydrogen-fueled fuel cell systems as portable powers. However, the long-term stability of MEAs remains a problem due to the degradation of components in either oxidizing or reducing environments. There is a growing body of literature concerning the long-term operation of DMFCs [4–11] and several factors are identified to date which influence the stable performance of DMFC including gradual loss of active electrocatalyst surface area caused by sintering [4] and poisoning due to reaction intermediates or impurities [5,6], cathode activity loss due to surface oxide formation [7–9], degradation of membrane and membrane/electrode interface, ruthenium crossover from the anode to the cathode through the membrane [10], variation of hydrophobic and hydrophilic properties in catalyst and gas diffusion layer [11], etc. * Corresponding author. Tel.: þ82 2 958 5275; fax: þ82 2 958 5199. E-mail address: hyha@kist.re.kr (H.Y. Ha). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he 0360-3199/$ – see front matter ª 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2008.10.092 international journal of hydrogen energy 34 (2009) 2043–2051