nonprecious catalysts toward the hydrogen evolution reaction (HER) for a widespread of sustainable energy storage and conversion. [6] To date, a variety of nonprecious-metalbased catalysts, especially, the family of earth-abundant transition metal compounds of nitrides, [7,8] carbides, [9,10] chalcogenides, [11][12][13][14] and phosphides, [15][16][17][18][19] have been explored for HER catalysts. It has been reported that novel material designs relying on chemical synthesis or crystalline engineering (facets, polymorph, interface, defect, doping, surface modification) can enhance HER activity. Nonetheless, in order to avoid the undesired charge transfer loss and gas bubble trap, a welldesigned, atomically and electronically coupled interface between fully tailored catalyst morphology and high surface area of conductive support turned out to be essential. [20] In this regard, unlike widely used oxygen functionalized carbon supports with severely damaged electrical properties, electron-rich N-doped carbon nanotubes (CNTs) and graphene not only provide additional electrons to graphitic carbons to maintain high electroconductivity but also afford novel synthesis platform for the synergistic hybrid structures of ultimate practical utilization. [12] We present a unique nanostructured core-shell hybrid catalysts composed of transition metal phosphosulfide (CoP@PS, MoP@PS, CoMoP@PS) decorated at N-doped carbon nanotubes (NCNTs). Nanoscale thick amorphous MS x (M = Co, Mo, CoMo) layers were directly deposited on the large area NCNT surfaces by low-temperature wet chemical process and subsequent phosphidation. Quasi-amorphous phosphosulfide (PS) nanoshells are formed around the crystalline core particles, whose S-doping effect greatly enhances the HER activity of nanoparticles to attain the noticeable HER activity of ≈ −80 mV @ −10 mA cm −2 with excellent durability. It is noteworthy that this is the first report for core-shell transition metal phosphosulfide nanostructure formation with a clear evolution of amorphous PS surface. The underlying catalytic mechanisms were investigated by density functional theory (DFT), which revealed the principal role of hybrid interfaces for the catalytic activity. Taken together, this hybrid offers one of the highest active nonnoble metal electrocatalysts ever reported thus far.A cost effective hydrogen evolution reaction (HER) catalyst that does not use precious metallic elements is a crucial demand for environment-benign energy production. The family of earth-abundant transition metal compounds of nitrides, carbides, chalcogenides, and phosphides is one of the promising candidates for such a purpose, particularly in acidic conditions. However, its catalytic performance is still needed to be enhanced through novel material designs and crystalline engineering. Herein, a chemically and electronically coupled transition metal phosphosulfide/N-doped carbon nanotubes (NCNT) hybrid electrocatalyst is fabricated via a two-step synthesis. The uniquely designed synthesis leads to the materia...