Redox-Based Cation Intercalation for a Large-Scale Production for Metallic Transition Metal Dichalcogenides

Chemical cation intercalation is a promising method for scaling up 2D materials via liquid exfoliation. For group-6 TMDs, this process induces a phase transition from natural trigonal prismatic (2H) to octahedral (1T), transforming their electronic properties from semiconducting to metallic. Solutions of 1T-TMDs have demonstrated excellent capabilities for creating electrochemical devices, such as batteries and catalytic systems. The most widely-used method involves the organolithiation agent n-butyllithium (n-BuLi), first demonstrated 50 years ago. While highly successful in various lab-scale applications, the slow reaction time and pyrophoric nature of n-BuLi have hindered the rational scale-up of liquid exfoliation. Here, we investigate this reaction on the nano- to mesoscale using in-situ optical microscopy, ex-situ optical techniques, X-ray photoemission spectroscopy (XPS), and electrochemical lithiation/sodiation, elucidating the roles of photons and redox potential. We demonstrate that polyaromatic hydrocarbons with appropriate redox potentials and alkali metals can replace pyrophoric n-BuLi in this chemical process. Additionally, we expand our strategy to sodium intercalation. Finally, by combining low-cost visible light with our newly synthesized redox metalization agents, we achieve a rapid cation intercalation reaction, presenting a feasible route for large-scale production of exfoliated TMDs in the solution phase.