Fabrication of Sulfonated Cellulose Nanocrystal/MXene Hybrid Proton Exchange Membrane and Its Synergistic Effect in Vanadium Redox Flow Battery

The vanadium redox flow battery (VRFB) is an attractive technique for renewable energy storage and output, and the proton exchange membrane is the vital component that determines battery performance. In this work, by incorporating sulfonated cellulose nanocrystals (SCNC)/MXene hybrids into a polymer matrix of poly vinylidene fluoride-<i>co</i>-hexafluoropropylene (PVDF-HFP), a proton exchange membrane was designed and fabricated, possessing a low vanadium permeability of 4.92 × 10^-9 cm² min^-1, improved proton conductivity of 15.8 mS cm^-1, and ion selectivity of 3.21 × 10⁶ S min cm^-3. The synergy between SCNC and the MXene nanosheet significantly elevates VRFB performance, yielding coulomb efficiency from 97.0% to 98.2%, voltage efficiency from 83.07% to 93.44%, and energy efficiency between 81.6% and 90.7% at a current density of 40-120 mA cm^-2, which are better than those of the commercial Nafion 212 membrane. The SCNC/MXene/PVDF-HFP hybrid membrane presents comprehensive superior battery performances, positioning it as a promising candidate for proton exchange membranes in VRFBs.