An Novel Anion Exchange Membrane with Accelerated Hydroxide Ions Conduction through Quaternized Covalent Organic Framework Doped Electrospinning Binary Polymer

Abstract

The mutual restriction between hydroxide ions conductivity and alkaline stability is the main obstacle for the practical application of anion exchange membranes (AEMs) in anion exchange membrane fuel cells. In this research, we design a binary polymer nanofibers of polyvinylidene fluoride (PVDF) and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (SEBS) through the electrospinning technique. A quaternized covalent organic framework (QACOF) is synthesized to accelerate the hydroxide ions conduction though consisting of successive and hydrophilic hydroxide ions conduction channels based on the quaternary ammonium groups. Additionally, the ordered microchannel structures of QACOF can further accelerate the hydroxide ions conduction process. The novel AEMs are thus constructed via re-stacking of PVDF-SEBS binary polymer nanofibers with the designed QACOF. The QACOF can be closely adhered to PVDF-SEBS binary polymer nanofibers even if the PVDF-SEBS/1%QACOF membrane was immersed in 2 M of KOH solution for 480 h. As a result, the single fuel cell equipped with the PVDF-SEBS/1%QACOF membrane exhibits the maximum power densities of 89.8 mW/cm2 at 30 °C and 264.2 mW/cm2 at 60 °C. Particularly, the reinforced hydroxide ions conduction and remarkable conductivity stability at subzero temperature have been realized owing to the confine of hydroxide ions conduction by chemically inert PVDF-SEBS binary polymer nanofibers. For instance, the hydroxide conductivity of the PVDF-SEBS/1%QACOF membrane is 2.58 mS/cm at -25 °C and retained to 32.4 mS/cm at 80 oC in a 480 h test.