High-performance membrane for vanadium redox flow batteries: Cross-linked poly(ether ether ketone) grafted with sulfonic acid groups via the spacer

We propose a new cross-linking agent grafted with -SO3H groups via side chain spacer by sultone group ring-opening reaction. The effective cross-linking of sulfonated poly(ether ether ketone) (SPK) has been achieved by sulphonamide bonding. In the reported methodology, during cross-linking -SO3H groups (2 functional groups per cross-linked repeating units) are consumed, which are compensated by -SO3H groups present in the cross-linking agent. Different cross-linked membranes are evaluated for vanadium redox flow battery applications. Reported membrane exhibits good synergetic balance between proton conductivity and vanadium permeability (ion selectivity). In single cell vanadium redox flow battery at 80 mA cm(-2), sulfonic acid grafted cross-linked SPK membrane shows higher coulombic efficiency (98%) and energy efficiency (85%) in comparison with Nafion117 membrane (93%, and 80%, respectively). The coulombic efficiency and energy efficiency values for reported membrane have been also compared with other membranes reported in the literature for the vanadium redox flow battery applications under similar operating environment. Reported membrane shows almost stable charge-discharge performance in single cell vanadium redox flow battery even after 120 number cycles. Proposed strategy provides a promising membrane fabrication strategy for vanadium redox flow battery.