Design, synthesis and characterization of anion exchange membranes containing guanidinium salts with ultrahigh dimensional stability

Anion exchange membranes (AEMs) with high anionic conductivity and mechanical robustness are required for alkaline membrane fuel cells (AMFCs) and are significantly influenced by the water uptake (WU) of the membrane. When the swelling ratio (SR) becomes too large, the mechanical integrity of the membrane becomes compromised, which may have catastrophic consequences for the fuel cell. Herein, backbone Poly(arylpiperidinium) (PAP) with no ether bond, rigidity and hydrophobic structure was combined with the hydrophobic guanidinium salt to design and synthesize a series of AEMs containing novel guanidinium salts through a simple and efficient route. The introduction of the guanidinium salt structure with large steric hindrance significantly improved the dimensional stability of the AEMs; the WU of membrane material at 80 °C was under 12%, and the SR was less than 3%. In addition, the AEMs showed excellent thermal stability, with the decomposition temperatures of the guanidinium group and the backbone being 350 °C and 450 °C, respectively.