Robust branched Poly(p-terphenyl isatin) anion exchange membranes with enhanced microphase separation structure for fuel cells

Abstract

Anion exchange membrane fuel cells (AEMFCs) are gradually becoming the focus of sustainable hydrogen energy research due to the advantages of clean by-products, faster oxidation-reduction dynamics and allowing cheap platinum-free base materials. As the key components of AEMFCs, anion exchange membranes (AEMs) are required to have high ionic conductivity and dimensional stability. This study focused on the design and preparation of branched AEMs for AEMFCs. The b-PTIN-x membranes were generated by incorporating 1,3,5-triphenylbenzene (TPB) units into rigid poly(p-terphenyl isatin) (PTI) polymer backbones. This innovative approach aimed to induce microphase separation structures by exploiting TPB with high FFV, as well as to enhance the tensile strength of AEMs with the help of branched structures. SAXS and AFM images revealed that the AEMs achieved enhanced microphase separation structures, resulting in the formation of ion transport channels with dimensions in the range of a few nanometers (3.36–3.70 nm). The branched b-PTIN-11 membranes displayed significant OH⁻ conductivity (153.9 mS cm⁻¹ at 80 °C) while having a low ion exchange capacity (IEC) (1.73 mmol g⁻¹). The b-PTIN-11 membranes displayed improved tensile strength (56.69 MPa) and exceptional dimensional stability, with swelling ratio (SR) of 18.5 % at 80 °C. They also showed great chemical stability with 89.64 % conductivity remaining, lasting for more than 1200 h in 3 M NaOH solution at 80 °C. Ultimately, the b-PTIN-11 membrane underwent testing to evaluate its performance in a fuel cell using H₂–O₂. It demonstrated a peak power density (PPD) of 566 mW cm⁻² when subjected to a current density of 1339 mA cm⁻².