Ultrafine Mo2c-Mo2n Heterojunction Anchored on Three-Dimensional Porous N-Doped Carbon Framework for Hydrogen Evolution Reaction and Lithium-Ion Batteries

Mo 2 C has been attracting numerous attentions for energy conversion and storage applications due to its similar electronic structure as Pt and high capacity. However, its high-temperature synthesis procedure always led to a large-size bulk, resulting in low catalytic utilization and stability. Herein, a series of Mo 2 C, Mo 2 C-Mo 2 N or Mo 2 N nanocrystals evenly integrated within three-dimensional (3D) porous N-doped carbon (N-C) are rational designed via regulating the ratio of polyvinyl pyrrolidone and melamine. Remarkably, the promoting synergistic effect of Mo 2 C-Mo 2 N heterojunction and the ultrasmall size expose abundant active sites, maximizing the utilization of catalysts and resulting in high catalytic activity. Then, the 3D N-C framework provide a bi-continuous electron/ion pathways, large surface area for catalytic reactions, as well as robust structural integrity, boosting catalytic reaction kinetics. Thanks to these advantages, the Mo 2 C-Mo 2 N/N-C sample exhibits low overpotential (44 mV) and Tafel slope (33 mV dec -1 ) comparable to those of commercial Pt/C in hydrogen evolution reaction (HER) in alkaline solution. Additionally, it also shows a high specific capacity, good rate capability and cycling stability as an anode material for lithium-ion batteries (LIBs). This work demonstrates the superiority of ultrafine heterojunction in 3D porous carbon-based composites to boost the electrochemical performance in various fields.