Unique Three-dimensional Mo₂C@MoS₂heterojunction Nanostructure With S Vacancies As Outstanding All-pH Range Electrocatalyst For Hydrogen Evolution

With the fossil fuels consuming and environmental pollution exacerbating,there is an urgent need for the renewable and clean alternative energy resources,among which hydrogen?H₂?is regarded to be a promising one.Water electrolysis is an eco-friendly technique to yield H₂,relying on the crucial half reaction?hydrogen evolution reaction,HER?using effective catalysts.Pt-based materials are recognized as the best HER electrocatalysts,whereas transition metal-based compounds,such as phosphides,carbides,nitrides and sulfides,are preferable owing to their rich sources and low cost.Herein,an unique and facile approach is introduced to fabricate three-dimensionalMo₂C@MoS₂heterojunction nanostructure?3D Mo₂C@MoS₂NS?with high concentration sulphur vacancies?SVs?via three-pot annealing of precursors which can be regarded as performance-intensive HER catalyst at all pH.The unique method is that irreplaceable 2D carbon sheets are served as sacrificial templates to form the intermediate Mo₂C nanostructure?Mo₂C NS?and the following partial surface vulcanization treatment.Besides,the density functional theory further indicates that the SVs confined in the 3D Mo₂C@MoS₂ NS could lowertheGibbs free energy of H adsorption(?G_H*),leading to increased HER performance.Thus the 3D Mo₂C@MoS₂NS with rich defects as an all-pH HER catalyst makes a major breakthrough in hydrogen evolution.This work highlights the progress compared to prior reports about cheap HER catalysts from the following three aspects,including unique three-dimensional heterojunction nanostructure,high concentration of SVs and enhanced HER performance under the whole pH conditions.1.On the one hand,three-dimension structure is equipped with favorable electrochemistly conductivity,due to its high specific surface area and high mechanical strength.On the other hand,unique heterojunction nanostructure with strong electronic interactions,which decreases the interfacial contact resistance and accelerates the transfer rate of electrons,thereby elevating the impressive catalytic activities.2.The introduction of SVs to improve the catalytic activity play an important role.The basal planes?002?of MoS₂ are exposed and they are equipped with high concentration SVs,leading to the exposure of the outer Mo-edge sites and providing rich active sites for HER catalysis.3.3D Mo₂C@MoS₂ NS is a promising material as HER electrocatalyst over a wide pH range.In this contribution,it is applied as an all-pH HER catalyst and demonstrates superb performance.Concretely,the resultant 3D Mo₂C@MoS₂ NS manifests low?₁₀ of 67,121 and 86 mV in 0.5 M H₂SO₄,1 M PBS and 1 M KOH.The corresponding Tafel slopes are as low as 37,46 and 39 mV dec^-1,which are superior to those of the reported all-pH non-noble-metal catalysts.Furthermore,it exhibits continuous stability?a slight current decay of<3%over 120 h?at the entire pH values.Notably,3D Mo₂C@MoS₂ NS can endure an extensive temperature variation,greatly broadening the HER application.All the results mentioned above suggest that the as-fabricated electrocatalysis is a valuable all-pH catalyst for HER,which has never been reported before.And it would open a new avenue for the development of energy conversion and storage technology.