Preparation of poly(arylene ether ketone) based anion exchange membrane with pendant pyrimidinium and pyridazinium cation derivatives for alkaline fuel cell

As a key constituent of anion exchange membrane fuel cells, anion exchange membrane (AEM) faces a tough challenge to withstand the nucleophilic (OH − ) attack on central cation in alkaline atmosphere which causes a constant degradation and thus affects the long term performance of the AEM. Aromatic cations unlike aliphatic amine cations are resistant to Hofmann β-elimination, however due to planar geometry they are more vulnerable to nucleophilic substitution reaction . To understand the problem and to formulate a mechanism to protect the AEM, a series of cationic membranes was fabricated based on poly(arylene ether ketone) having pendant quaternized derivatives of pyrimidinium and pyridazinium cations employing DCC-coupling reaction. The chemical structure characterization of the target products was conducted by 1 H NMR and FT-IR spectroscopy. Various physicochemical properties of the membranes were investigated including thermomechanical behavior, ion exchange capacity, water uptake, swelling ratio, ionic conductivity , fuel cell performance and oxidative and chemical stabilities. No serious swelling was observed with adequate water uptake at temperature between 20 °C and 80 °C. The membranes with both pyrimidinium and pyridazinium cations exhibited sufficient ionic conductivity . The highest recorded conductivity was 45.7 mS cm −1 and peak power density was 194 mW cm −2 . The oxidative stability of all membranes was high (more than 90%) however, alkaline stability results suggest a different behavior. Pyridazinium cations with substituents simultaneously at C-3 and C-6 positions is thoroughly protected from OH − attack while pyrimidinium (simultaneously protected at C-4 and C-6 positions) degraded at accelerated rate with raising temperature. This work not only explores the possibility of utilizing aromatic cations that weren't used before but also provides a wider understanding of the relationship of aromatic cation structure and membrane stability and performance thus helping in designing stable anion exchange membranes for long-lasting fuel cells.