Glycine betaine intercalated layered double hydroxide modified quaternized chitosan/polyvinyl alcohol composite membranes for alkaline direct methanol fuel cells

Abstract

Utilization of chitosan as the host polymer of anion exchange membranes (AEMs) can avoid the carcinogenic chloromethylation step which is indispensable for aromatic polymers during their quaternization process. To further improve the ionic conductivity and mechanical stability, a hydroxide ion conductor (layered double hydroxides, LDHs) was intercalated by glycine betaine and then incorporated to quaternized chitosan and polyvinyl alcohol mixed matrix to prepare AEMs. Due to intercalated organic ions, the LDHs can be homogeneously dispersed in the matrix, thus promoting the load transfer from the matrix to stiff LDHs. The tensile strength and elongation of the composite membrane (5% intercalated LDHs content) are 23.6 MPa and 51.4% which are 71% and 44% respectively higher than those of the pure QCS/PVA membrane. Moreover, the hydroxide ion conductor (LDHs) and the intercalated quaternary ammonium groups could act as new OH− conductive sites and further enhance the ionic conductivity. The membrane with 5 wt.% intercalated LDHs loading shows ionic conductivity of ˜35.7 mS cm−1 (80 °C) and peak power density of 97.8 mW cm−2 which are respectively 42% and ˜50% higher than those of the pure membrane. Furthermore, better alkaline stability was also proved in the composite system, and the ionic conductivity of the composite membrane can retain 70% (only 49% for the pure membrane) even after immersing in a 1 M KOH for 168 h.