Stabilizing metastable 1T MoS2 via electrochemical proton intercalation for hydrogen evolution reaction

Abstract

Hydrogen evolution reaction (HER) is currently the most efficient industrial method for producing clean, nontoxic, and environmentally friendly hydrogen using effective optimal electrocatalysts. In particular, Transition metal dichalcogenides are promising candidates for HER electrocatalysts due to their unique 2D layered structure. Among them, molybdenum disulfide (MoS2) stands out for its optimal structural and electronic properties, as well as its flexibility. These properties greatly enhance HER activity and enable the exploration of various MoS2 phases, which demonstrate HER activity comparable to that of platinum (Gibb’s free energy [ΔGH∗]: ∼0.08 eV), emphasizing their prominence as high-performance electrocatalysts. One of these phases is 1T (tetragonal) MoS2, which exists in a metallic form and exhibits catalytic activity at both its edge and basal sites. This activity can be significantly enhanced by effectively stabilizing its behavior to prevent its restacking into 2H (hexagonal) MoS2. In this study, a simple electrochemical proton intercalation method is used to enhance the properties of 1T MoS2. Notably, the proton-intercalated 1T MoS2 demonstrates an excellent electrocatalytic HER performance, achieving the lowest overpotential of 187 mVRHE at 10 mA∙cm−2 and the smallest Tafel slope of 48 mV∙dec−1. Additionally, it demonstrates durability for up to 60 h in a 0.5 M H2SO4 electrolyte at a current density of 10 mA∙cm−2. Density functional theory calculations confirm that proton intercalation significantly influences material behavior and increases the interplanar distance, thereby enhancing the hydrogen (H∗) adsorption performance and lowering the ΔGH∗ value. Charge transfer analysis confirms that charge accumulation at the active sites facilitates rapid proton reduction, which correlates with increased electron mobility and efficient catalytic turnover. The proton-intercalated 1T MoS2 also demonstrates an increased density of states at the Fermi level, confirming its high conductivity and its role as the most optimal HER electrocatalyst among the polymorphs. This increased conductivity facilitates improved charge transfer efficiency at the catalyst-electrolyte interface, which contributes to more effective proton reduction.