Journal of Power Sources 159 (2006) 524–528 Short communication Preparation and charateristics of Nafion membrane coated with a PVdF copolymer/recast Nafion blend for direct methanol fuel cell Ki-Yun Cho a , Ho-Young Jung a , Kyung A. Sung a , Wan-Keun Kim a , Shi-Joon Sung a , Jung-Ki Park a,∗ , Jong-Ho Choi b , Yung-Eun Sung c a Department of Chemical and Biomolecular Engineering, Korea Advanced Institute of Science and Technology, 373-1, Guseong-Dong, Yuseung-Gu, Daejon 305-701, South Korea b Department of Materials Science & Engineering, Kwangju Institute of Science and Technology, Gwangju 500-712, South Korea c School of Chemical Engineering & Research Center for Energy Conversion & Storage, Seoul National University, Seoul 151-744, South Korea Received 13 July 2005; accepted 31 October 2005 Available online 4 January 2006 Abstract In order to enhance the compatibility between the electrode and the membrane and also to reduce the methanol cross-over from the anode to the cathode in direct methanol fuel cells, a Nafion membrane coated with a poly(vinylidene fluoride) copolymer/Nafion blend has been prepared and characterized. The coated Nafion results in a reduction in methanol cross-over and an enhancement in cell performance due to its improved compatibility with the electrodes. © 2005 Elsevier B.V. All rights reserved. Keywords: Coating layer; Poly(vinylidene fluoride) copolymer/Nafion blend; Electrode–membrane compatability; Methanol cross-over; Direct methanol fuel cell 1. Introduction Perfluorosulfonate ionomer membranes such as Nafion, Dow XUS and Flemion are used for proton-exchange membranes in fuel cells owing to their good electrochemical stability, sat- isfactory mechanical strength and high proton conductivity. When such membranes are applied to direct methanol fuel cells (DMFC), methanol cross-over from the anode to the cathode is usually significant. This cross-over not only wastes fuel but also causes performance losses at the cathode due to the consumption of oxygen and catalyst poisoning. Efforts to decrease methanol cross-over have focused on improvement of the polymer elec- trolyte membrane. Some new membranes have been shown to be successful in reducing the methanol cross-over [1–4], but they either sacrifice the mechanical strength of the native Nafion or increased the cell resistance due to poor compatibility between the membrane and electrode. ∗ Corresponding author. Tel.: +82 42 869 3965; fax: +82 42 869 3910. E-mail address: jungpark@kaist.ac.kr (J.-K. Park). Poly(vinylidene fluoride) (PVdF) copolymer is miscible with Nafion-like ionomers [5,6]. In addition, the PVdF copolymer has sufficient mechanical strength and dimensional stability, and lower reactant permeability [7]. In this study, Nafion is coated with a layer that consists of a blend of vinylidene fluoride- hexafluoropropylene copolymer (PVdF copolymer) and recast Nafion. The effect of the coating layer on the electrochemical properties is investigated. 2. Experimental 2.1. Materials A PVdF copolymer with 85 mol% vinylidene fluoride (Kynar Flex 2751, Mn = 380,000) was supplied from Atofina Chem- icals Inc. The Nafion 117 membranes and 20 wt.% Nafion (1000 g eq -1 ) solutions in a mixture of isopropanol, n-propanol and water were purchased from E.I. Dupont de Nemours & Co. The Nafion 117 membrane was pretreated as reported elsewhere [8]. The Nafion solution was used as received. Dimethylfor- mamide (DMF) and methanol were purchased from Merck and 0378-7753/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2005.10.106