Conductivity and Water Uptake of Aromatic-Based Proton Exchange Membrane Electrolytes

Water uptake and proton conductivity as a function of temperature were determined for three aromatic‐based, sulfonic acid‐bearing polymers, plus the perfluoroalkyl sulfonic acid Nafion® 117. Water uptake of submerged, equilibrated samples ranged from less than five water molecules per acid group for a high equivalent weight, sulfonated polyethersulfone to almost fifty waters per acid for a low equivalent weight, sulfonated polyetheretherketone. The most conductive aromatic‐based polymer, sulfonated polyphenylquinoxaline (S‐PPQ), had a room temperature conductivity of . about an order of magnitude less than that of a perfluoroalkyl sulfonic acid under identical conditions. The slope of the S‐PPQ Arrhenius conductivity plot was sufficiently steep that at 180°C, the proton conductivity, , was only a factor of two lower than that of Nafion under similar conditions. The lower conductivity of the aromatic‐based sulfonic acid polymers can be attributed to chain rigidity, lack of ion channels, and lower acidity. © 2000 The Electrochemical Society. All rights reserved.