Ultrathin MoS₂ Membrane with Low Stacking Fault for Vanadium Redox Flow Battery

Vanadium redox flow battery (VRFB) is one of the most promising sustainable large-scale energy storage systems. In VRFB, a membrane with high proton/vanadium ion selectivity and high proton conductivity is essential for improved cycle life, energy efficiency, and power density of the entire cell. Commercial Nafion membranes are commonly used, but they require a high cost even though they have low ion selectivity and swelling issues. In this study, we applied MoS₂ as a VRFB membrane material due to its excellent chemical stability. The MoS₂ is vacuum-filtered on porous polymer support to prepare ultrathin membranes, but poor dispersion stability of MoS₂ flakes in solvents has resulted in membrane defects during the filtration process. To decrease the stacking fault, we employed graphene oxide as an additive and used a different solvent system to stabilize the MoS₂ dispersion. As a result, the prepared MoS₂ membranes showed lower vanadium crossover and better chemical stability than the commercial Nafion membrane.