Regulating Surface Structure Of Vanadium-based Compounds For Enhanced Electrocatalytic Properties

The demand for clean and sustainable energy promotes the exploitation of hydrogen energy.Water splitting technology has attracted wide attention from researchers as an ideal and efficient HER technology,but the challenge of this technology is to find a suitable electrocatalyst.At present,Pt-based catalysts have exhibited the best HER performance,but the low content on the earth and high cost limit its wide applications.Therefore,developing efficient and cheap hydrogen evolution electrocatalysts which can replace Pt-based precious metals is of great research significance.Recent years,many excellent electrocatalysts for HER have been reported,such as carbides,nitrides,sulfides,phosphides,and etc.,among these species,vanadium carbide?VC?and vanadium nitride?VN?have similar electronic structures to Pt,they are considered as potential alternatives to Pt electrocatalyst,however,there are only a few reports based on them,studying on designing VC and VN electrocatalysts for improved electrocatalytic properties has great room for development.However,the water splitting reaction is mainly carried out on the surface of the catalysts,so the catalytic performance of the electrocatalyst is closely related to the surface structure.In this thesis,regulating the surface structure of electrocatalysts was used as the approach to design and synthesize VC@NCNT,Mo-VC and VCoN as HER electrocatalysts,and the relationship between surface structure and electrocatalytic properties of the catalysts was clarified.The main conclusions of this thesis include the following three parts:?1?Dicyandiamide,ammonium metavanadate and cobalt nitrate hexahydrate were used as raw materials,a metal-triggered confinement strategy was adopted to synthesize ultrasmall VC nanoparticles embedded within N-doped carbon nanotubes?VC@NCNT?.The synthesis mechanism of VC@NCNT,the influence of carbonization temperature on the phase,morphology,crystallinity and surface chemical state of samples were also investigated.It was clarified that Co,Ni and Fe all can induce in-situ synthesis of carbon nanotubes and ultrasmall VC nanoparticles.As-prepared VC@NCNT exhibits high catalytic HER performance at a wide pH values?pH 0¹4?,and the Faraday efficiency is close to 100%.?2?Dicyandiamide,ammonium metavanadate and ammonium molybdate were used as raw materials,Mo-doped ultrasmall VC nanoparticles?Mo-VC?was prepared by a one-step calcination method.The regulation of Mo-doping on Mo-VC?s electronic structure was studied,the relationship between Mo-doping and electrocatalytic HER performance of Mo-VC was explored,suggesting that Mo-doping has an enhanced effect on the HER performance of VC.?3?Porous vanadium nitride nanoplates?VCoN?were successfully obtained by solid phase reaction using urea,ammonium metavanadate,as well as cobalt nitrate hexahydrate as starting materials.The influence of calcination temperature on the synthesis of sample,as well as the effects of Co on the crystallinity,surface chemical state and porosity of VCoN were revealed.It was first reported that VCoN can act as a highly efficient HER electrocatalyst.At pH 14,VCoN requires an overpotential of only 179 mV at 10 mA/cm² and it can work at least 100 h.Comparing with VN(?₁₀=476 mV),the catalytic activity of VCoN has been greatly improved.