Semi-Interpenetrating High-Temperature Proton Exchange Membranes Based on Cross-Linked Poly(fluorenyl-terphenyl-piperidinium) and Poly(vinylbenzyl chloride-co-vinylbenzyl chloride) for Fuel Cells

Current proton exchange membranes (PEMs) for proton exchange membrane fuel cell (PEMFC) application exhibit performance deterioration at high temperatures, but the high-temperature operation of PEMFCs has many advantages. To prepare high-temperature PEMs (HT-PEMs) with high conductivity, good thermal stability, and mechanical properties, 1,6-dibromohexane is used as the cross-linking agent to construct a cross-linked network skeleton (cPFTP) based on poly(fluorenyl terphenyl piperidinium). A linear polymer poly(vinylbenzyl chloride- co -vinylbenzyl chloride) (PSVIm-VBC) containing sulfonated imidazole groups is synthesized and inserted into the cross-linked network to construct a series of HT-PEMs with a semi-interpenetrating polymer network (semi-IPN). Compared with the cross-linked cPFTP membrane, membranes with a semi-IPN structure promoted phosphoric acid (PA) doping. When the PSVIm-VBC content of the membrane accounted for 40% of the total polymer mass, the PA uptake of the PFTP/PSVIm-VBC-40% membrane was 171.7%. At 160 °C, the proton conductivity of the PFTP/PSVIm-VBC-40% membrane reached 174.93 mS cm –1, which was 2.8 times that of cPFTP, and the PA retention rate was 84.21% after 72 h. All the fuel cells have a high open voltage (>0.8 V), which proves that the membranes we have prepared have excellent fuel separation ability. The fuel cell with a PFTP/PSVIm-VBC-40% membrane achieved a high power density of 487.61 mW cm –2 at 140 °C. The construction of this semi-IPN structure provides facile insights into the design of high-performance HT-PEMs.