Author's personal copy Porous layered oxide/Nafion Ò nanocomposite membranes for direct methanol fuel cell applications Yeny Hudiono a , Sunho Choi b , Shu Shu a , William J. Koros a , Michael Tsapatsis b , Sankar Nair a, * a School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332-0100, USA b Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA article info Article history: Received 12 August 2008 Received in revised form 14 September 2008 Accepted 15 September 2008 Available online 23 September 2008 Keywords: Direct methanol fuel cell (DMFC) Polyelectrolyte exchange membrane (PEM) Porous materials Layered silicates Layered aluminophosphates abstract Nanocomposite membranes were prepared by exfoliating, intercalating and/or dispersing nanoporous layered aluminophosphate or silicate materials in Nafion Ò . Specifically, the layered aluminophosphate- triethylamine (APO-TE), aluminophosphate-isopropanolamine (APO-IPA), aluminophosphate-imidazole (APO-ImH), and the swollen layered silicate AMH-3, were used as selectively permeable barriers that can potentially block methanol permeation but maintain proton conductivity in the membrane. The pres- ence of the layered materials in Nafion Ò membranes reduced the methanol permeability by up to an order of magnitude while maintaining proton conductivities close to that of neat Nafion Ò at room tem- perature. Small-angle X-ray scattering (SAXS) characterization shows substantial differences in micro- structure of the nanocomposite membranes from that of neat Nafion Ò . The performance of the nanocomposite membranes was also found to be strongly dependent on the membrane pre-treatment conditions. Detailed comparison of our data to the previous literature indicates that for certain conditions of membrane preparation, the proposed approach yields promising results in controlling methanol and proton transport through membranes for direct methanol fuel cell (DMFC) applications. Ó 2008 Elsevier Inc. All rights reserved. 1. Introduction Significant rises in fossil fuel costs and global environmental concerns continue to increase the demand for new energy sources as well as better methods of energy utilization. Fuel cells are con- sidered one of the viable alternatives for energy utilization, notably to generate power for automotive and portable electronics applica- tions. A number of different types of fuel cells have been developed [1]. One of the most widely investigated types of fuel cells is the proton exchange membrane fuel cell (PEMFC), also known as a polyelectrolyte membrane fuel cell. It utilizes a polymeric electro- lyte membrane (PEM), e.g. made of Nafion Ò , to conduct protons be- tween the anode and the cathode. The protons are generated by the catalytic oxidation of the fuel at the anode. In hydrogen-based PEMFCs, molecular hydrogen (H 2 ) is used as the fuel. The genera- tion and compression/storage of hydrogen for such fuel cells is a subject of extensive ongoing research [2]. On the other hand, alco- hols such as methanol and ethanol (which can be manufactured from natural gas or biomass) can also be used as fuels. In this case, an alcohol/water mixture is catalytically oxidized at the anode to generate protons for conduction through the PEM. In particular, the direct methanol fuel cell (DMFC) utilizes methanol as the fuel, and is attractive for several reasons. It can operate in a wide tem- perature range (up to 150 °C); and it uses a liquid or vapor fuel that is easy to generate and store, and which has a much higher energy density (per unit volume) than compressed hydrogen. The DMFC is suitable for portable/mobile devices such as cell phones and lap- tops because it can deliver about 10 times the power density of a lithium battery [3] and does not require recharging (only a meth- anol fuel cartridge replacement). A number of companies have developed prototypes of cellular phones, laptops, and portable cameras powered by DMFCs [4]. It is envisaged that the worldwide market for DMFC technology will reach $2.6 bn by 2012 [5]. Although much progress has been made in DMFC technology, there are significant challenges to be overcome. The energy conver- sion efficiency of DMFCs is still low; only 32–40% of the chemical energy is converted to electrical energy. This is primarily due to two reasons: (i) the high rate of methanol loss by permeation (crossover) through the PEM and (ii) the low methanol oxidation rate at the anode. This paper is concerned with membranes that re- duce methanol crossover. In addition to causing fuel wastage, the unoxidized methanol (that reaches the cathode by crossover from the anode) also affects the activity of the cathode catalyst for the reduction of oxygen to water. Ultimately, high methanol crossover decreases the overall efficiency and lifetime. Hence, low concentra- tions of methanol (<10 vol%) are used, whereas it is desirable to use much higher concentrations at the anode to reduce the volume of fuel required with no concurrent loss of efficiency. Recent work has also suggested that fuel crossover may be one of the necessary fac- 1387-1811/$ - see front matter Ó 2008 Elsevier Inc. All rights reserved. doi:10.1016/j.micromeso.2008.09.017 * Corresponding author. E-mail address: sankar.nair@chbe.gatech.edu (S. Nair). Microporous and Mesoporous Materials 118 (2009) 427–434 Contents lists available at ScienceDirect Microporous and Mesoporous Materials journal homepage: www.elsevier.com/locate/micromeso