Hierarchical layered double hydroxide coated carbon nanotube modified quaternized chitosan/polyvinyl alcohol for alkaline direct methanol fuel cells

Abstract

Cost-effective and eco-friendly biopolymer chitosan has been attracted the rising interest as a promising anion exchange membrane material because it can be easily quaternized without involving the carcinogenic chloromethylation step that is inevitable for polyaromatics. Ionic conductivity and mechanical strength are the two main concerns for the high-performance application of quaternized chitosan. Herein, we report hydroxide ion conductor (layered double hydroxide, LDH) coated carbon nanotubes (LDH@CNTs) as a multifunctional nanofiller to modify quaternized chitosan and polyvinyl alcohol blend matrix. The hierarchical nanostructure of LDH@CNTs consisting of two-dimensional LDH nanosheets anchored on one-dimensional carbon nanotubes plays a good reinforcing role. Incorporating 1 wt% of LDH@CNTs shows a 1.57-fold increase in tensile strength. Moreover, owing to the unique one-dimensional structure of carbon nanotubes as well as the excellent hydroxide-conducting ability of LDH coating, the channel-like ion transport pathways can be constructed and thus enhance the ionic conductivity of the composites. The composite membrane with 1 wt% LDH@CNTs loading exhibits conductivity of 47 mS cm−1 (80 °C) and maximum power density of 107.2 mW cm−2 (2 M methanol + 5 M KOH, 80 °C) which are respectively 61% and 27% higher than those of the pure membrane.