Engineering Mixed-Phase MoS₂ Quantum Dots toward Accelerated Hydrogen Evolution

The hydrogen evolution reaction (HER) requires efficient, low-cost, and durable catalysts to enable sustainable hydrogen production. Among transition-metal dichalcogenides, MoS₂ has attracted considerable attention due to its promising catalytic properties. However, the catalytic performance of conventional MoS₂ is often restricted by the limited activity of basal planes and the poor electrical conductivity of the thermodynamically stable 2H phase. Phase engineering has emerged as an effective strategy to overcome these limitations by introducing metallic 1T domains and creating 1T/2H heterophase interfaces, which enhance charge transport and increase the number of accessible active sites.

In this work, mixed-phase 1T/2H MoS₂ quantum dots (QDs) are investigated as efficient HER electrocatalysts. The combination of phase coexistence and quantum-dot nanostructuring provides enhanced catalytic activity through improved conductivity and high surface-area exposure. Structural and chemical analyses using X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and high-resolution transmission electron microscopy (HRTEM) confirm the successful formation of nanoscale QDs and the coexistence of both 1T and 2H phases. The synthesized QDs exhibit size distributions in the few-nanometer range, with representative average sizes of ~3.5, ~12.6, and ~28.4 nm depending on synthesis conditions.

Electrochemical measurements in acidic media demonstrate excellent HER performance, characterized by a low onset potential of approximately 42 mV and a Tafel slope of ~90 mV·dec⁻¹, indicating favorable reaction kinetics. The catalyst also shows remarkable durability, maintaining stable activity after extensive cycling and continuous operation for up to 14 h. The best-performing sample achieves a hydrogen evolution rate of ~1700 μmol·L⁻¹·h⁻¹, together with a large electrochemically active surface area (ECSA ~350.6 cm²) and a high turnover frequency (TOF ~0.212 s⁻¹ at −0.3 V vs RHE). These results highlight the strong synergistic effect between mixed-phase engineering and quantum-dot morphology, positioning 1T/2H MoS₂ QDs as promising catalysts for efficient hydrogen evolution.