High conductivity poly(meta-terphenyl alkylene)s proton exchange membranes for high temperature fuel cell

Phosphoric acid (PA)-doped membranes are regarded as a promising candidate for high temperature proton exchange membranes (HT-PEMs), but the trade-off between mechanical property and conductivity is a major problem limiting their application. Here, two poly(meta-terphenyl alkylene)s (m-TPNs), namely m-TPN-MeIm and m-TPN-TMA, are synthesized by 1-methylimidazole (MeIm) and trimethylamine (TMA) reacting with precursor polymer, respectively. The influence of different cationic groups on the properties of m-TPNs HT-PEMs is investigated in detail. m-TPNs diminish plastication of PA molecules on the mechanical property by separating the adsorption sites for PA molecules from the polymer backbone through long alkyl side chains. As a result, both m-TPN-MeIm and m-TPN-TMA membranes exhibit good mechanical property. Besides, m-TPN-TMA/PA surpasses m-TPN-MeIm/PA in most of aspects owing to the higher ion exchange capacity (IEC) and more distinct microphase separation structure. Noticeably, the proton conductivity of m-TPN-TMA/PA is as high as 0.191 S cm−1 and exhibits excellent stability over a testing time of 100 h at 160 °C thanks to the remarkable acid uptake and microphase separation structure. The m-TPN-TMA/PA-based single cell produces an impressive peak power density of 552 mW cm−2 at 200 °C. Therefore, this work offers a viable alternative for structure design to mitigate the trade-off effect of PA-doped HT-PEMs.