Biaxial Strained MoS₂ Nanoshells with Controllable Layers Boost Alkaline Hydrogen Evolution

Strain in layered transition-metal dichalcogenides (TMDs) is a type of effective approach to enhance the catalytic performance by activating their inert basal plane. However, compared with the traditional uniaxial strain, the influence of biaxial one and TMDs layer number on local electronic configuration remains unexplored. Herein, via a new <i>in situ</i> self-vulcanization strategy, we realize biaxial strained MoS₂ nanoshells in the form of single-crystalline Ni₃S₂@MoS₂core-shell heterostructure, where the MoS₂ layer is precisely controlled between 1 to 5 layers. In particular, the electrode with bilayer MoS₂ nanoshells shows a remarkable hydrogen evolution reaction activity with a small overpotential of 78.1 mV at 10 mA cm^-2, and negligible activity degradation after durability test. Density Functional Theory calculations reveal the contribution of optimized biaxial strain together with the induced sulfur vacancies, and identify the origin of superior catalytic sites in these layer-resolved MoS₂ nanoshells. This work highlights the importance of the atomic-scale layer number and multiaxial strain in unlocking the potential of two-dimensional TMDs electrocatalysts.