Amino acid clusters supported by cellulose nanofibers for proton exchange membranes

Abstract

Inspired by the structure of amino acid residues chain in transmembrane proteins, amino acid molecules are immobilized onto cellulose nanofibers to form clusters as quasi-one dimensional proton-conducting pathways for nanofiber hybrid proton exchange membranes. The structure of conducting clusters and properties of the hybrid proton exchange membranes are examined. The results show that the amino acid clusters enhance the proton conductivity, and the proton exchange membrane with Ser-clusters shows the highest proton conductivity of 0.264 S/cm at 80 °C under 100% humidity and temperature. Diffusion coefficients and mean square displacements of hydronium ion are then calculated using Density-Functional Tight-Binding method to better understand the proton-conducting mechanism of amino acid clusters, and the results of molecular dynamics simulation are in good agreement with the experiments. Besides, the structure of three-dimensional hydrophilic network of nanofibers exhibits significant effect on the performance of water uptake, dimensional stability, methanol permeability and thermal stability of the hybrid proton exchange membranes. Fuel cell performance test confirms that these membranes are suitable for direct methanol fuel cells.