Phosphonate ionic liquid immobilised SBA-15/SPEEK composite membranes for high temperature proton exchange membrane fuel cells

Abstract

High temperature proton exchange membrane fuel cells require an electrolyte membrane which is mechanically and thermally more stable for its efficient performance. In the present study, a composite membrane prepared using phosphonate ionic liquid immobilised SBA-15 as filler and SPEEK as matrix has been reported. The imidazolium ionic liquid namely 1-Methyl-3-(3- Trimethoxysilylpropyl) imidazolium chloride was grafted on SBA-15 followed by reacting with monosodium phosphate to afford phosphate ion (H2PO4−) containing SBA-15 (PIL-SBA-15). The structure of PIL-SBA-15 was confirmed by solid state CP/MAS 13C and 31P NMR, FTIR, low angle XRD, BET and TEM analyses. SPEEK composite membranes with different concentrations (2, 4, 6 and 8 wt%) of PIL-SBA-15 was prepared by simple solution casting method. The change in morphology of the composite membranes were studied using SEM and XRD techniques. The ion exchange capacity, proton conductivity at high temperatures and water uptake of the composite membranes increased in the presence of PIL-SBA-15. The membrane with 6% fillers showed the maximum electrochemical performance with superior mechanical strength. Upon testing this composite membrane as electrolyte in fuel cell using platinum as both anode and cathode electrodes under un-humidified condition, a maximum power density of 183 mW/cm2 was achieved at 140 °C. The existence of additional ion exchange groups (H2PO4−) lead to the improved performance at high temperature. Keywords: High temperature polymer electrolyte, SBA-15, Ionic liquid grafting, Fuel cell performance and un-humidified fuel cell