Constructing proton exchange membranes with high and stable proton conductivity at subzero temperature through vacuum assisted flocculation technique

Abstract

The application of proton exchange membranes in low temperature proton exchange membrane fuel cells requires the quick and stable proton conduction at subzero temperature. In this research, we constructed the multilayered membranes through the alternate deposition of poly(vinyl alcohol) (PVA), Kevlar nanofibers and carbon nanotube oxides (OCNTs) through the vacuum assisted flocculation (VAF) technique. The intermolecular hydrogen bonds resulted in the preparation of (PVA/Kevlar/OCNTs)3 membranes with layered structure. Phosphoric acid (PA) molecules entered the gaps between the neighboring layers accompanying with the phase separation. The prepared membranes exhibited the high and stable proton conductivity at subzero temperature, such as 2.04 × 10-2 S/cm at −30 °C and 1.52 × 10-1 S/cm at 30 °C. The proton conductivity gradually changed to 5.52 × 10-2 S/cm and 1.84 × 10-1 S/cm even after the ten-cycles process of −30 °C–30 °C. In addition, the value can retain 1.42 × 10-2 S/cm at −30 °C in a 1900 h non-stop test. The evaporation and liquefaction of water molecules could affect proton conductivity besides PA dominating the proton conduction behavior during heating/cooling processes. Furthermore, the balance on low temperature proton conduction and mechanical strength makes the multilayered (PVA/Kevlar/OCNTs)3/PA membranes as a promising PEM candidate at subzero temperature.