Abstract
A series of quaternized polysulfone (QPSF) blended with ZSM-5 zeolite anion exchange membrane were fabricated by solution casting for application as separators in aluminium-air (Al-air) battery. The prepared membranes in this study are the pristine QPSF, QPSF/ 1 wt.% ZSM-5, QPSF/3 wt.% ZSM-5, and QPSF/5 wt.% ZSM-5. The prepared QPSF, ZSM-5, and QPSF/ZSM-5 membranes were characterised by proton nuclear magnetic resonance (1H NMR), Fourier-transform infrared (FTIR) spectroscopy, Scanning electron microscopy (SEM), thermogravimetric analysis (TGA), and X-ray diffraction (XRD) spectroscopy.
1H NMR and FTIR spectra confirmed the successful chloromethylation and quaternisation of polysulfone. XRD and FTIR were used to confirm the formation of ZSM-5 zeolite. TGA and SEM were used to investigate the thermal stability and surface morphological composition. QPSF and ZSM-5 were directly blended for QPSF/ZSM-5 composite membranes fabrication. The increase in ZSM-5 content from 1 to 3 wt. % were found to smoothen the QPSF/ZSM-5 membranes.
Critical electrolyte and separator properties such as hydrophilicity, water uptake (WU), swelling ratio (SR), ion exchange capacity (IEC), ion conductivity (IC), and alkaline stability were evaluated for QPSF and QPSF/ZSM-5 composite membranes. All membranes exhibited moderate to excellent WU, SR, IEC, and IC measurements. The incorporation of ZSM-5 introduced hydrophilicity and enhanced water uptake with QPSF/ 3% ZSM-5 retaining 114 % water at room temperature. The QPSF/3 wt.% ZSM-5 composite membrane was the best performing membrane with the IEC, highest hydration number, and maximum IC of 2.85 mmol g-1, 2.23, and 229.85 mS.cm-1, respectively. QPSF/ 3 wt.% ZSM-5 retained 65 % of its initial IC in an alkaline media after seven days. QPSF/3 wt.% ZSM-5 exhibited a stable discharge voltage of 1.3 V and a specific capacity of 11716 mAh/gAl in our laboratory made Al-air cell. This study offers an excellent anion exchange composite membrane separator candidate for Al-air battery application.