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.