Electro‐osmotic Drag of Water in Ionomeric Membranes: New Measurements Employing a Direct Methanol Fuel Cell

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Abstract
A direct methanol fuel cell (DMFC) employing a proton conducting membrane was used to determine the electro‐osmotic drag coefficient of water in the ionomeric membrane. Water flux across the membrane in such a cell (operated with 1.0 M aqueous methanol at the anode and dry at the cathode) is driven by protonic drag exclusively at sufficiently high current densities. This is evidenced experimentally by a linear relationship between cell current and flux of water measured crossing the membrane. Application of the DMFC for such water‐drag measurements is significantly simpler experimentally than the approach described by us before, particularly so for measurements above room temperature. In measurements we performed in the DMFC configuration on Nafion® 117 membranes, the water drag coefficient was found to increase with temperature, from 2.0 at 15°C to 5.1 at 130°C. Implications of these new results on water management in DMFCs are briefly discussed.