Polymers of intrinsic microporosity with alkaline pyrrolidine and piperidine functional groups for high-temperature proton exchange membranes

Abstract

Recently, the polymers of intrinsic microporosity (PIMs) exhibit good potential in high-temperature proton exchange membrane fuel cells (HT-PEMFCs) due to their tunable microporosity and functionality. In this paper, alkaline pyrrolidine and piperidine functional groups were introduced onto PIM-1 via the classical Mannich reaction obtaining PIM-1/PIM-Py-50 and PIM-1/PIM-MePi-50. It was found that, compared with commercial Meta-polybenzimidazole (m-PBI) membrane, PIMs membranes showed superior retention of phosphoric acid (PA) and conductivity due to their grafting alkaline groups and rich micropores. After equilibration under 80 °C/40% relative humidity (RH) for 150 h, the PA retention of PA doped PIM-1/PIM-Py-50 (PIM-1/PIM-Py-50/PA) and PA doped PIM-1/PIM-MePi-50 (PIM-1/PIM-MePi-50/PA) membranes were 74.13% and 68.52%, respectively, much higher than PA doped m-PBI (m-PBI/PA) (45.73%). PIMs membranes maintain excellent dimensional and conductivity stability at 160 °C operating conditions, e.g. PIM-1/PIM-Py-50/PA membrane showed area swelling retention and volume swelling retention of 84.69% and 82.19% after 230 h at 160 °C. In addition, with the similar PA uptake, PIMs membranes displayed higher conductivity and peak power density (PPD) at 160 °C. In the accelerated stress test (AST) the PPD of the fuel cell (FC) with the PIM-1/PIM-Py-50/PA membrane remained 81.25% after 200 aggressive start-up/shut-down cycles at 80 °C. Therefore, PIM-based membranes alkaline groups exhibit a wider temperature operating window, providing theoretical guidance for the design and study of the next generation of high-temperature proton exchange membranes (HT-PEMs).