Long side-chain N-heterocyclic cation based ionic liquid grafted poly (terphenyl piperidinium) membranes for anion exchange membrane fuel cell applications

Anion exchange membrane fuel cells (AEMFCs) bring out unique advantages including the use of cheap and plentiful catalytic materials, fast oxygen reduction reaction rate at cathode and low cost of membranes. However, the development of performing and durable anion exchange membranes (AEMs) is still the major challenge for the ultimate industrial adoption of AEMFC. Herein, the ether-free poly(p-terphenyl-co-N-methyl-piperidine) (PTP) is synthesized and employed as the matrix for AEM. Four ionic liquids of long side-chain N-heterocyclic cations bromide are synthesized and chosen as the quaternization reagents for PTP. Thus, four flexible and long side-chain cationic groups grafted PTP based AEMs are fabricated. The effect of end-group cations on the properties of long side-chain AEMs has been investigated systematically. The presence of long side-chain cations endows AEMs with high conductivity and low swellings simultaneously. Among all the membranes, N-methyl-piperidinium grafted AEM (PTP-C5-MPi) exhibits the highest alkaline stability owing to ether-free polymer chain, long side-chain linkage and piperidinium cation, which retains 87 % of its original ion conductivity after storage in 1.0 M KOH solution for 2118 h. Furthermore, the H2-O2 fuel cell based on PTP-C5-MPi is performed to determine the technical feasibility.

Automated summary

Anion exchange membrane fuel cells (AEMFCs) offer advantages such as using cheap catalytic materials, fast oxygen reduction reaction, and low-cost membranes. However, developing durable anion exchange membranes (AEMs) remains a major challenge. In this study, an ether-free polymer was synthesized and used as the matrix for AEM. Four ionic liquids were synthesized and used as quaternization reagents for the polymer. The resulting AEMs exhibited high conductivity and low swellings. One particular AEM showed excellent alkaline stability and retained high ion conductivity after prolonged storage in a KOH solution. Furthermore, a fuel cell based on this AEM was tested and showed technical feasibility.