Electro-osmotic drag of water in poly(perfluorosulfonic acid) membranes

Direct methanol fuel cells (DMFCs) using poly(perfluorosulfonic acid) membr anes were used to determine the water electro-osmotic drag coefficients in these ionomeric membranes. In a DMFC fed with 1.0 M aqueous methanol at the anode and dry O-2 at the cathode, the ionomeric membrane can be fully equi librated on both sides with liquid water at a sufficiently high current den sity. In this special situation, the water flux across the membrane from an ode to cathode is driven by protonic drag exclusively From measurements per formed on Nafion(R), C(R), and Dow(R) membranes, water drag coefficients of all membranes increase with temperature. Compared with a fully hydrated me mbrane, a dried membrane (105 degreesC in vacuum) known to have a lower wat er content has a lower water drag coefficient. For a series of Nafion membr anes (including C membrane), a membrane with a higher equivalent weight has a lower water drag coefficient. The water drag coefficient of a Dow membra ne is unusually low compared to that of a Nafion membrane of similar equiva lent weight. These trends of water drag coefficients may correlate with the membrane structure and water content. Implications of these results on wat er management in polymer electrolyte fuel cells are discussed. (C) 2000 The Electrochemical Society. S0013-4651(99)11-013-9. All rights reserved.