Journal of Membrane Science 259 (2005) 27–33 Pd electroless plated Nafion ® membrane for high concentration DMFCs Hai Sun a,d , Gongquan Sun a,∗ , Suli Wang a,d , Jianguo Liu d , Xinsheng Zhao a,d , Guoxiong Wang a,d , Hengyong Xu c , Shoufu Hou c , Qin Xin b a Direct Alcohol Fuel Cell Laboratory, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Zhongshan Road 457, Dalian 116023, China b State Key Laboratory of Catalysis, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China c 801 Group, Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China d Graduate School of the Chinese Academy Sciences, Beijing 100039, China Received 14 December 2004; received in revised form 5 February 2005; accepted 8 February 2005 Available online 6 June 2005 Abstract A Pd layer was deposited on Nafion ® membrane by electroless plating in order to reduce methanol crossover. The composite membrane was characterized by using the following techniques of X-ray diffraction (XRD), scanning electron microscope (SEM), energy dispersive X-ray spectrometer (EDXS) and transmission electron microscopy (TEM). Methanol crossover was determined by the electrochemical method. The experimental results indicated that Pd film was successfully deposited onto the Nafion ® membrane. The methanol permeability was effectively suppressed by the Pd layer, with methanol-related current decreasing from 64 mA/cm 2 (J lim ) to 57 mA/cm 2 for 1 M methanol and from 267 mA/cm 2 to 170 mA/cm 2 for 5M methanol, respectively. Furthermore, by employing the novel Pd-Nafion ® composite electrolyte, the performance of single fuel cell was obviously improved with a high concentration of methanol such as 5 M, indicating that depositing Pd layer onto the Nafion ® membrane is an effective method to suppress the methanol crossover. © 2005 Elsevier B.V. All rights reserved. Keywords: DMFC; Methanol crossover; Pd; Electroless plating 1. Introduction There is a growing interest in the research of direct methanol fuel cells (DMFCs) as portable power sources and electric devices due to their high energy density and simplic- ity in the system structure such as easy storage and supply of fuel and needing no fuel reforming or humidification [1–3]. It is known that Nafion ® perfluorosulfonic acid poly- mers are commonly used as the electrolyte due to their good chemical and thermal resistance and ionic conductivity in DMFCs [4,5]. Unfortunately, the present perfluorosulfonate membranes are known to be quite permeable to methanol, leading to methanol crossover to the oxygen cathode in the DMFCs, causing depolarization losses at the cathode and fuel losses and consequently poor performance. In order ∗ Corresponding author. Tel.: +86 411 84379063; fax: +86 411 84379063. E-mail address: gqsun@dicp.ac.cn (G. Sun). to improve the performance of DMFCs, it is necessary to eliminate or at least to reduce methanol crossover to some extent. Recently, considerable effort has been focused on this problem. Additionally, the unique properties of palladium mem- brane which is permeable to protons, yet completely resistant to the transport of methanol are very promising and accom- modate to the requirement of a solid electrolyte, which can be utilized in DMFCs. Pu et al. [6] investigated the performance of composite membranes that were formed by sandwich- ing a dense Pd foil (25 m thick) between two Nafion ® 115 membranes. Though the Pd-sandwiched membrane was active for proton transport and methanol crossover was elim- inated, the performance of a PEMFC with the membrane was still very poor. Choi et al. [7] reported a study on the DMFCs performance with Pd-layered Nafion ® membrane. The thin palladium films were deposited onto the surface of Nafion ® 117 membrane using a sputtering technique. The 0376-7388/$ – see front matter © 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.memsci.2005.02.017