Soluble poly(aryl piperidinium) with extended aromatic segments as anion exchange membranes for alkaline fuel cells and water electrolysis

Superacid-catalyzed polymerization of N-methyl-4-piperidone and aromatic hydrocarbons followed by quaternization is regarded as a reliable synthetic pathway to prepare anion exchange membrane (AEM) materials with superior conductivity and excellent alkaline stability, which is crucial for their application in alkaline fuel cells and alkaline water electrolysers. In this work, we design and prepare soluble p-quaterphenyl-containing poly(aryl piperidinium) (PQP-100) to increase the rigidity and hydrophobicity of aryl ether-free polymer backbones. Consequently, robust PQP-100 AEM exhibits improved microphase-separated morphology as conformed by SAXS and AFM observation. In comparison with biphenyl and p-terphenyl-based poly(aryl piperidinium), PQP-100 AEM possesses high hydroxide conductivity (118.72 mS/cm at 80 °C) and ability to be fabricated ultrathin membrane up to 4 μm without reinforcement. 75% of original conductivity is maintained for PQP-100 membrane after 1344 h of alkaline stability test in 1 M NaOH at 80 °C due to the degradation of piperidiniums via nucleophilic substitution. The practical device performance of PQP-100 membrane shows a peak power density (PPD) of 496 mW/cm2 in H2/O2 fuel cells at 60 °C and a current density of 1544 mA/cm2 at 2.0 V in alkaline water electrolysers circulating 1 M KOH at 85 °C, and the thinner membranes reduce the output of both fuel cells and electrolysers. Moreover, the durability of fuel cell and electrolyser at 200 mA/cm2 also manifest the performance loss over 85 and 402 h of operation, mainly attributed to the chemical degradation of PQP-100 membrane as evidenced by post-cell analysis using NMR technology.