Quantum Dots of 1T Phase Transitional Metal Dichalcogenides Generated via Electrochemical Li Intercalation

We prepare group VI transitional metal dichalcogenides (TMDs, or MX₂) from the 1T phase with quantum-sized and monolayer features via a quasi-full electrochemical process. The resulting two-dimensional (2D) MX₂ (M = W, Mo; X = S, Se) quantum dots (QDs) are ca. 3.0-5.4 nm in size with a high 1T phase fraction of ca. 92%-97%. We attribute this to the high Li content intercalated in the 1T-MX₂ lattice (mole ratio of Li:M is over 2:1), which is achieved by an increased lithiation driving force and a reduced electrochemical lithiation rate (0.001 A/g). The high Li content not only promotes the 2H → 1T phase transition but also generates significant inner stress that facilitates lattice breaking for MX₂ crystals. Because of their high proportion of metallic 1T phase and sufficient active sites induced by the small lateral size, the 2D 1T-MoS₂ QDs show excellent hydrogen evolution reactivity (with a typical η₁₀ of 92 mV, Tafel slope of 44 mV/dec, and J₀ of 4.16 × 10^-4 A/cm²). This electrochemical route toward 2D QDs might help boost the development of 2D materials in energy-related areas.