Xiaoming Yan,Runlian Deng,Yu Pan,Xiaowei Xu,Issam El Hamouti,Xuehua Ruan,Xuemei Wu,Ce Hao,Gaohong He
Hydroxide exchange membrane fuel cells (HEMFCs) are attracting growing interest owing to their advantages such as low cost and high power density. However, their applications are hindered due to the poor stability of the membrane. Here, we proposed a novel strategy to improve the alkaline stability of hydroxide exchange membranes (HEMs) using the interactions between strongly polar nitrile groups and side-chain functional cations. A poly(ether nitrile) (PEN) was synthesized by the polycondensation of bisphenol A and 2,6-difluorobenzonitrile, and then imidazolium and morpholinium functional groups were integrated by the typical chloromethylation-functionalization method. The existence of the interactions between nitrile groups and cation groups i.e. imidazolium and morpholinium, was proved by the density functional theory calculations. The interactions have two positive effects that contribute to the improvement of the alkaline stability of the PEN based membranes. On the one hand, they increase the LUMO energies of the functional groups; and on the other hand they reduce the free volume around hydrated cationic groups. As a result, PEN based membranes showed much better alkaline stabilities compared to the membrane based on commercial polysulfone that has a similar chemical structure . In addition, given similar swelling ratios, PEN based membranes exhibited higher hydroxide conductivities than simple polysulfone based ones.
Aromatic nucleophilic substitution polymerization was used to synthesize five poly(ether nitrile imide)s (PENIs) that include benzonitrile and bulky cardo groups from a mixture of phenolphthalein (PP), 4,4′-bis(4-fluorophthalimide) diphenyl ether (4,4′-BFPI), and 2,6-difluorobenzonitrile (DFBN). The structure and properties relationship of PENIs with different ratios of DFBN and 4,4′-BFPI was explored. It was found that the glass transition temperature ( T g ) of PENIs decreased from 280 to 260°C, while the temperature of 5% thermal weight loss ( T 5% ) in N 2 increased from 429 to 453°C as the benzonitrile content in PENI increased. The produced PENI films had good mechanical characteristics, including tensile strengths of 103–112 MPa, elongations at break of 5.6%–8.2%, and tensile moduli of 2.9–3.4 GPa. Furthermore, the solubility and melt processability were also improved with the introduction of the benzonitrile group. Compared with poly(ether ketone imide)s (PEKIs) and poly(ether sulfone imide)s (PESIs), PENIs with benzonitrile displayed higher T g , tensile modules, and lower complex viscosity.
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