Nafion-Mediated Liquid-Phase Exfoliation of Transition Metal Dichalcogenides and Direct Application in Hydrogen Evolution Reaction

Owing to its mass-production capability and simple process, liquid-phase exfoliation (LPE) of layered bulk materials is commonly used for synthesizing two-dimensional materials, such as graphene or transition metal dichalcogenides (TMDs). Surfactants are often used in LPE process to improve the exfoliation efficiency and dispersion stability of target materials. However, during the surfactant-mediated exfoliation process, the as-applied surfactant typically forms strong covalent/noncovalent bonds with target materials, thereby deteriorating the properties of starting materials. Rinsing the surfactants can also be problematic because the decreased dispersion of the exfoliated flakes leads to restacking. Therefore, the contradictory phenomenon between maintaining the dispersion stability and preserving the material property has been a demanding issue in the LPE process of two-dimensional materials. Herein, a surfactant assisted LPE of molybdenum disulfide (MoS2) using Nafion as the surfactant in environmentally friendly water solution is introduced. Nafion, which contains both hydrophilic and hydrophobic moieties, not only helps the exfoliation process of MoS2, but also prevents the exfoliated MoS2 from reaggregation. The Nafion-assisted exfoliated MoS2 is successfully demonstrated as the electrocatalyst in hydrogen evolution reaction without requiring any additional binder and surfactant rinsing process. The dual role of Nafion as the dispersing agent and binder is verified by experimental analyses and theoretical calculations. The proposed approach is expected to provide a useful guide in the application of two-dimensional materials prepared via surfactant-assisted LPE process.