Highly Selective Proton Exchange Membrane Enabled by Organically Modified MXene for Vanadium Flow Battery

For the proton exchange membrane (PEM) applying in vanadium flow battery (VFB), it is difficult to separate the electrolyte ions at two electrodes while conducting protons. In this work, a novel composite membrane is developed, organically modified‐MXene (MDP) filled sulfonated poly(ether ether ketone) (SPEEK) membrane, where MDP is prepared through co‐coating the polydopamine (PDA) and polyethyleneimine (PEI) on the surface of MXene. The two‐dimensional structure of MXene can effectively reduce the vanadium ions permeation, while the surface functional groups from the coating layer can assist in proton transport, thus enhancing the membrane selectivity. The membrane with only 1.0 wt% MDP (SPEEK/MDP‐1) achieves maximum selectivity of 7.1 × 10 7 S min cm −3 . Furthermore, the energy efficiency (EE) of the VFB loaded with SPEEK/MDP‐1 reaches ~92.5% at 40 mA cm −2 current density. This work provides a new direction for enhancing the properties of PEM used in VFB applications.