Enhanced performance of a passive direct methanol fuel cell with decreased Nafion aggregate size within the anode catalytic layer Ting Yuan a,b , Yongying Kang a,b , Ji Chen a , Chong Du a , Yongjin Qiao a , Xinzhong Xue a, *, Zhiqing Zou a , Hui Yang a, * a Shanghai Institute of Microsystem and Information Technology, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 200050, China b Graduate School of the Chinese Academy of Sciences, Beijing 100039, China article info Article history: Received 26 January 2011 Received in revised form 6 May 2011 Accepted 10 May 2011 Available online 25 June 2011 Keywords: Nafion ionomer Aggregation Membrane electrode assembly Catalyst utilization Direct methanol fuel cell abstract The decrease in Nafion ionomer size within the anode catalytic layer for a passive direct methanol fuel cell (DMFC) results in a significant enhancement in fuel cell’s performance. Dynamic light scattering measurement demonstrates that the agglomerate size of Nafion ionomer in the solution decreases and the aggregate particle size distribution becomes narrow until a monodispersed Nafion ionomer was obtained with an increase in heat treatment temperature. The improved performance of the passive DMFC with smaller Nafion ionomer agglomerates within the anode catalytic layer can be ascribed to a decrease in charge-transfer resistance of anodic reaction obtained by electrochemical impedance analysis and to an improvement in catalyst utilization verified by cyclic voltammetric measurement. Furthermore, the small congeries formed between catalyst nanoparticles and Nafion ionomers could lead to a decrease in Nafion loading within the catalytic layer. This study confirms that the decrease in Nafion aggregation within the catalytic ink is beneficial to an improvement in both catalyst and Nafion ionomer utilization, thus enhancing fuel cell’s performance. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction The direct methanol fuel cell (DMFC) has attracted much attention as potential power sources due to its high energy density, low pollution, as well as availability and easy fuel- recharging [1,2]. The passive DMFC is regarded as an prom- ising candidate for its portable applications because some auxiliary devices, such as the liquid pump for the fuel feed and the gas compressor for the oxidant supply, are unnecessary in a passive DMFC system, which helps to decrease the volume of the fuel cell system and to increase the achievable energy density and power density [3]. However, there are several issues that have restricted its practical applications: e.g., sluggish kinetics of methanol oxidation reaction, relatively low power density and expensive catalyst and polymer elec- trolyte [2,4]. As a key component of a DMFC, the membrane electrode assembly (MEA) plays an important role in determining a better performance of the fuel cell, in which the electro- chemical reactions take place at the three-phase boundary zone consisting of catalyst, reactants and electrolyte. Many investigations have focused on the use of novel nanosized * Corresponding authors. Fax: þ86 21 32200534. E-mail addresses: xuexz@sari.ac.cn (X. Xue), yangh@sari.ac.cn (H. Yang). Available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 36 (2011) 10000 e10005 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.05.059