Ion transfer channel network formed by flower and rod shape crystals of hair hydrolysate in poly(vinyl alcohol) matrix and its application as anion exchange membrane in fuel cells

摘要

Ion transfer phenomena occurring in nature are known to be most efficient. Many efforts have been made to mimic such phenomena, especially in the area of energy transfer. Proteins consisting of various amino acids are known to be the fundamental materials behind these phenomena. In the current study, an effort was made to extract proteinaceous material from human hair bio-waste by a green chemical-free thermal hydrolysis process. A simple heat treatment of the human hairs in presence of water led to the formation of a water soluble material, which was called hair hydrolysate (HH), contains 70 wt% proteinaceous material. It was utilized for the fabrication of poly(vinyl alcohol) (PVA) matrix-based anion exchange membrane (AEM). Presence of 27 wt% charged amino acids and 19 wt% polarizable amino acids in the HH provided effective charge transfer sites. 7 wt% arginine present in the HH, having continuous delocalized net positive charge helped the membrane to be stable in highly alkaline conditions, which was confirmed by an indirect analysis of alkaline stability. Formation of rod and flower shaped crystal morphology by the HH in glutaraldehyde crosslinked PVA matrix, created a continuous channel network at higher loadings, which provided a simple path for ion transfer, achieving OHconductivity of 7.46 mS/cm at 70 degrees C. Swelling of the PVA matrix was minimized by annealing of the HH loaded sample, which resulted in reduction of ionic conductivity to 6.16 mS/cm (at 70 degrees C). At the same time, improvement in the properties like increase in thermal, mechanical and thermo-mechanical stability, reduction in water uptake, %swelling and methanol permeability was observed. The selectivity of the membrane was increased to almost a decimal place. Thus, the HH obtained from simple green thermal hydrolysis of human hair bio-waste is a cheap material, which is found to be suitable as ion conductive material for alkaline fuel cells. (c) 2020 Elsevier Inc. All rights reserved.