Electrospun\nSulfonated Poly(ether ether ketone) and\nChitosan/Poly(vinyl alcohol) Bifunctional Nanofibers to Accelerate\nProton Conduction at Subzero Temperature

Multilayered\nmicrostructures can accelerate the proton conduction\nprocess in proton exchange membranes (PEMs). Herein, we design and\nconstruct PEMs with microstructures based on bifunctional nanofibers\nand sulfonated poly(ether ether ketone) (SPEEK) nanofibers. Specifically,\nthe bifunctional nanofibers composed of poly(vinyl alcohol) and chitosan\nare prepared and then combined with the electrospun SPEEK nanofibers.\nThe stable microstructure is derived from the compatible interfacial\nproperty of nanofibers and the formed hydrogen bonds. The multilayered\nmicrostructure consisting of nanofibers accelerates the proton conduction\neven at subzero temperature because of regulating the proton conduction\npathways. Specifically, the (SKNF/CPNF/SKNF)/PA membrane exhibits\nthe proton conductivities of (0.951 ± 0.138) × 10<sup>–2</sup> S/cm at −30 °C and (7.32 ± 0.37) × 10<sup>–2</sup> S/cm at 160 °C. Additionally, the fine proton\nconductivity stability is demonstrated by the proton conductivity\nin the long-term test and the cooling/heating cycle test, such as\n1.67 × 10<sup>–2</sup> S/cm at −30 °C (after\n1000 h), 4.52 × 10<sup>–2</sup> S/cm at 30 °C (after\n810 h), 1.12 × 10<sup>–2</sup> S/cm at −30 °C,\nand 1.01 × 10<sup>–1</sup> S/cm at 30 °C in the cooling/heating\nprocess (5 cycles). The single fuel cell possesses an open-circuit\nvoltage of 0.886 V and a peak power density of 0.508 W/cm<sup>2</sup> at 130 °C.