Researching proton conduction behavior at subzero temperature of lamellar anhydrous proton exchange membranes

For proton exchange membranes (PEMs), many studies have been going into the anhydrous PEMs with the working temperature exceeding 110 °C and the humidified PEMs below 80 °C. However, the PEMs fracture can cause cold start failure while the fuel cell vehicles are exposed to a colder climate for a long-time parking. In this study, low temperature PEMs (LTPEMs) with the lamellar structure was constructed through the well-ordered dispersion of Kevlar nanofibers, thioglycollic acid capping cadmium telluride (CdTe) nanocrystals and polyurethane (PU) polymer, expecting to enhance the mechanical property and improve the proton conductivity at subzero temperature. The successful preparation of the LTPEMs with spin coating technique and layer by layer self-assembly technique was determined by the structure analysis and the property measurement. The compact microstructure was constructed owing to electrostatic attraction and intermolecular hydrogen bonding. In the prepared (Kevlar/CdTe) 25 /(PU/CdTe) 100 membrane, Kevlar nanofibers provided the support and PU molecular chains guaranteed enough flexibility. Furthermore, a massive amount of CdTe nanocrystals could tolerate low temperature condition, which was derived from the high proton conductivity at subzero temperature. Specifically, the (Kevlar/CdTe) 25 /(PU/CdTe) 100 /PA membrane exhibited the proton conductivity values of (2.23 ± 0.39)×10 −2 S/cm at −30 °C, (6.59 ± 0.15)×10 −2 S/cm at 0 °C and (1.73 ± 0.04)×10 −1 S/cm at 30 °C. Most importantly, the fine proton conductivity stability was revealed from the proton conductivity values of 3.72×10 −2 S/cm at −30 °C after a thirty-cycle heating/cooling process and 3.53×10 −2 S/cm at −30 °C after a 1020 h non-stop test. Furthermore, there was a slight decrease on the tensile stress with PA molecules doping owing to the compact microstructure. • Lamellar low temperature proton exchange membranes were prepared. • High and stable proton conductivity at subzero temperature was obtained. • PA doped membranes maintained enough mechanical stiffness.