Efficient proton-selective hybrid membrane embedded with polydopamine modified MOF-808 for vanadium flow battery

Membrane possessing high ion selectivity and proton conductivity is of great importance to the proper operation of energy storage techniques. Hereon, a hybrid membrane was prepared by doping polydopamine (PDA) modified MOF-808 into the sulfonated poly (ether ether ketone) (SPEEK) matrix. MOF-808 is a type of acid stable metal organic framework with abundant proton transport channels, while PDA forms a blocking shell on MOF-808, inhibiting the penetration of vanadium ions. In addition, the amino groups of PDA are beneficial to the proton transport, and at the same time the polymeric chains can be entangled with SPEEK thus improving the adhesion force between MOF and the matrix. As a consequence, an optimized hybrid membrane exhibited remarkable performance in the vanadium flow battery (VFB) with synchronous increase in coulombic efficiency as well as voltage efficiency, hence contributing to greatly enhanced energy efficiency (83.9%) surpassing the pristine SPEEK membrane (76.0%) and commercial Nafion212 (78.2%) at 120 mA cm⁻². This work demonstrates that controllable surface modification of the filler may serve as a useful approach for preparing high performance proton-selective hybrid membranes.