Aligned Heterointerface‐Induced 1T‐MoS 2 Monolayer with Near‐Ideal Gibbs Free for Stable Hydrogen Evolution Reaction

1T‐phase molybdenum disulfide (1T‐MoS 2 ) exhibits superior hydrogen evolution reaction (HER) over 2H‐phase MoS 2 (2H‐MoS 2 ). However, its thermodynamic instability is the main drawback impeding its practical application. In this work, a stable 1T‐MoS 2 monolayer formed at edge‐aligned 2H‐MoS 2 and a reduced graphene oxide heterointerface (EA‐2H/1T/RGO) using a precursor‐in‐solvent synthesis strategy are reported. Theoretical prediction indicates that the edge‐aligned layer stacking can induce heterointerfacial charge transfer, which results in a phase transition of the interfacial monolayer from 2H to 1T that realizes thermodynamic stability based on the adhesion energy between MoS 2 and graphene. As an electrocatalyst for HER, EA‐2H/1T/RGO displays an onset potential of −103 mV versus RHE, a Tafel slope of 46 mV dec −1 and 10 h stability in acidic electrolyte. The unexpected activity of EA‐2H/1T/RGO beyond 1T‐MoS 2 is due to an inherent defect caused by the gliding of S atoms during the phase transition from 2H to 1T, leading the Gibbs free energy of hydrogen adsorption (ΔG H* ) to decrease from 0.13 to 0.07 eV, which is closest to the ideal value (0.06 eV) of 2H‐MoS 2 . The presented work provides fundamental insights into the impressive electrochemical properties of HER and opens new avenues for phase transitions at 2D/2D hybrid interfaces.