N-Doped Sandwich-Structured Mo₂C@C@Pt Interface with Ultralow Pt Loading for pH-Universal Hydrogen Evolution Reaction

Designing a unique electrochemical interface to exhibit Pt-like activity and good stability is indispensable for the efficient hydrogen evolution reaction (HER). Herein, we synthesize well-defined Mo₂C@NC@Pt nanospheres with a sandwich-structured interface through a facile organic-inorganic pyrolysis and following reduction process. The obtained Mo₂C@NC@Pt heterostructures with ultralow Pt loading are composed of well-dispersed Mo₂C nanoparticles (NPs) inner layer, N-doped carbon layer, and ultrafine Pt NPs outer layer. Electrochemical measurements demonstrate that Mo₂C@NC@Pt heterostructures not only exhibit superior HER activities than commercial Pt/C with small overpotentials of only 27, 47, and 25 mV to achieve a current density of 10 mA cm^-2 in acidic, alkaline, and neutral media, respectively, but also possess favorable long-term stability in pH-universal solution. The improved reaction kinetics of Mo₂C@NC@Pt heterostructures are mainly attributed to the unique sandwich-structured interface with well-defined Mo₂C NPs encapsulated by carbon layers and Pt NPs well-dispersed on the carbon support, synergistic effects among Mo₂C NPs, NC, and Pt NPs, high specific surface area, and N-doping into the catalysts. This facile approach not only provides a new pathway for preparing well-defined carbides but also gives insight into the development of low-Pt catalysts for the efficient HER.