Abstract

 The structural engineering of 2D layered materials is emerging as a powerful strategy to design catalysts for high‐performance hydrogen evolution reaction (HER). However, the ultimate test of this technology under typical operating settings lies in the reduced performance and the shortened lifespan of these catalysts. Here, a novel approach is proposed to design efficient and robust HER catalysts through out‐of‐plane deformation of 2D heterojunction using metal‐organic chemical vapor deposition. High‐yield, single‐crystalline WTe_​2 nanobelts are used as an epitaxial template for their coherent conversion to WS_​2. During the conversion process, the WTe_​2/WS_​2 heterostructure containing both lateral and vertical junctions are achieved by coherent heteroepitaxial stacking despite differences in symmetry. The lattice coherency drives out‐of‐plane deformation of heteroepitaxially grown WS_​2. The increase in the effective surface area and decrease in the electron‐transfer resistance across the 2D heterojunctions in turn enhances the HER performance as well as the long‐term durability of these electrocatalysts.