(Invited) Biomimetic Proton Conductive Polymer Electrolyte

Abstract

Proton conductive polymer electrolyte is one of the key components to fabricate an efficient fuel cell. Perfluorosulfonic acid polymers, such as Nafion are widely used because of their high proton conductivity. It has been considered that a strong acid is important for high proton conductivity therefore many group synthesized acid contain polymer from the viewpoint of how much strong acid can be added with keeping the polymer mechanical strength. On the other hand, living cell, mitochondria also used proton to produce energy. The difference in proton concentration across a membrane produce electrochemical potential energy, which drives the synthesis of ATP. Mitochondria does not contain strong acid and the protons are transferred using weak acid and base, whereas efficient proton conduction occurred at the bilayer membranes. Although the detailed mechanism for the proton conduction at the membrane is still controversial, several groups suggested that protons efficiently conduct through the membrane surface [1]. In this paper, we present a polymer proton conductive membrane which mimic the proton conduction at the bilayer membrane [2]. The polymer membrane was prepared by deposition of poly(N-dodecylacrylamide-co-acrylic acid) monolayer formed at an air-water interface using the Langmuir-Blodgett technique. The membrane was formed by multilayer film of the monolayer, in which formed a clear lamellar structure composed of hydrophobic alkyl side chains and hydrophilic amide and carboxylic acid regions. The hydrophilic region created 2D proton conductive nanospace, which resembles to the bilayer membrane surface. The proton conductivity in the 2D proton nanospace of the biomimetic polymer membrane reached to 5.9×10-2 S/cm, which is comparable to strong acid polymer electrolyte. The achievement of high proton conductivity even using weak acid as a proton source clearly indicates an efficient proton conduction in 2D nanospace. Moreover, we found that acrylic acid groups should be located in a proper distance to achieve the high proton conductivity. The mechanism of proton conduction at the 2D nanospace will be discussed using reported works of theoretical calculation.