Pervaporation membranes in direct methanol fuel cells Bryan S. Pivovar * , Yuxin Wang, E.L. Cussler Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, MN 55455, USA Received 27 January 1998; received in revised form 17 August 1998; accepted 17 August 1998 Abstract The membranes in direct methanol fuel cells must both conduct protons and serve as a barrier for methanol. Na®on, the most common fuel cell membrane, is an excellent conductor but a poor barrier. Polyvinyl alcohol pervaporation membranes are good methanol barriers but poor conductors. These and most other pervaporation membranes offer no signi®cant advantages over Na®on in methanol fuel cell applications. However, polybenzimidazole membranes have demonstrated characteristics that suggest up to a 15-fold improvement in direct methanol fuel cells. This improvement may be due to an alternate form of proton conduction in which protons travel via a Grotthus or ``hopping'' mechanism. # 1999 Elsevier Science B.V. All rights reserved. Keywords: Barrier membranes; Batteries; Solubility and partioning; Fuel cells 1. Introduction This work explores the potential of pervaporation membranes in direct methanol fuel cells. Polymer electrolyte fuel cells require a membrane to separate the chemical reactions at the anode and the cathode. In direct methanol fuel cells, methanol is oxidized cata- lytically at the anode, producing carbon dioxide and protons. The protons migrate through the membrane and react catalytically with oxygen to produce water at the cathode. A successful fuel cell membrane must allow protons to move freely. This requirement has led many researchers to focus on cation exchange membranes. These membranes have ®xed anionic charges which often permit easy proton transport. The most com- monly used polymer has been a per¯uorinated sul- fonic acid membrane best known by its trade name Na®on. The generally accepted model for this polymer is that of a chemically stable, hydrophobic matrix ®lled with hydrophilic, sulfonic acid clusters con- nected by pores [1]. A successful direct methanol fuel cell membrane must not only conduct protons, but also prevent methanol transport. Methanol transported across the membrane can react at the cathode without producing electricity. This not only lowers fuel utilization, but also adversely effects cathode performance [2]. While ion exchange membranes typically have good proton conductivity, they can be poor methanol barriers. For example, fuel cells based on Na®on can leak up to 40% of the methanol, even though they are typically operated at low methanol concentrations. Therefore, membranes are needed which are both effective proton conductors and methanol barriers. We seek these membranes not by ®rst looking for high Journal of Membrane Science 154 (1999) 155±162 *Corresponding author. 0376-7388/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved. PII: S0376-7388(98)00264-6