Anhydrous Protonic Conductivity of a Self-Assembled Acid−Base Composite Material

Recently, anhydrous proton-conducting membranes have attracted remarkable interest for application to the polymer electrolyte membrane fuel cell (PEMFC) operated at intermediate temperature (100−200 °C). In this paper, we prepared the self-assembled acid−base composite material with the highly ordered molecular array through the hybridization of acidic surfactant monododecyl phosphate (MDP) and basic surfactant 2-undecylimidzole (UI) molecules. This UI−MDP composite material has been found to form highly ordered lamellar structures with a d spacing of approximately 40 Å and to construct two-dimensional proton-conducting pathways within the close-packed surfactant headgroups. As a result, UI−MDP lamellar composite materials showed a high proton conductivity of 1 × 10 -3 S cm -1 at 150 °C under the anhydrous condition. Additionally, the activation energy, 0.30−0.45 eV, of proton conduction was almost the same as for other materials reported as anhydrous single-proton conductors. These anhydrous proton-conducting materials without the existence of water molecules are quite different for ion-exchange membranes such as Nafion and may have advantages as an electrolyte membrane for PEMFC.