Study On Heterostructure Control And Electrocatalytic Performance Of Transition Metal-based Nanomaterials

The global environmental and energy crisis have attracted wide attention and led to continuous efforts to find sustainable energy storage and conversion systems that can meet the energy needs of modern society.Electrocatalytic water splitting derived from renewable energy sources has been identified as a potential and practical strategy for future energy production.However,this promising approach is limited by its slow reaction kinetics and high cost.The construction of low-cost and high-performance non-precious metal-based catalysts has become one of the most effective ways to solve these big challenges.In recent years,many non-precious metal based catalysts have been synthesized by various methods.The purpose,on the one hand,is to reduce the potential in the catalytic process so as to reduce the consumption of electric energy,and on the other hand,is to enhance the stability of the catalyst.However,the most reported electrocatalytic performance is not comparable to that of precious metal catalysts.Based on this problem,several transition metal-based electrocatalysts were constructed in this paper through the design of nanostructure.The construction of heterogeneous interface could enhance the catalytic performance so as to improve the performance of water splitting based on transition metal-based catalysts.The main research contents and results are as follows:(1)We have successfully prepared nitrogen-doped carbon-coated cobalt/vanadium nitride(Co/VN@N-C)nanospheres by means of a novel method.The reduction of Co2VO4/polydopamine(Co2VO4/PDA)was used to generate Co nanoparticles in situ,and the formation of VN nanocrystals was also provided with a nitrogen source of PDA.In addition,PDA carbonization led to the formation of N-C coating.The Co/VN@N-C nanosphere catalyst obtained excellent catalytic performance.(2)In this work,the ultrafine NiS₂/MoS₂ Janus subunits organized on the yolk-shell nanospheres were synthesized by a novel and facile approach.The greatly reduced particle size of both two dimensional MoS₂ and one dimensional NiS₂ on the ultrafine NiS₂/MoS₂ Janus subunits endowed the yolk-shell nanospheres with numerous intimate interfaces of the bimetal sulfide hybrids greatly promoting intimate electronic interaction and dissociation of water molecules.Benefiting from the ultrafine NiS₂/MoS₂ Janus subunits,abundant edge sites and the high density of interfaces,the as-prepared NiS₂/MoS₂ yolk-shell nanospheres exhibited high electrocatalytic activity with a low?10 of 135 and 293 m V for hydrogen evolution reaction(HER)and oxygen evolution reaction(OER),respectively.Meanwhile,a low cell voltage(1.58 V)was achieved by using NiS₂/MoS₂ yolk-shell nanospheres as both anode and cathode.This study has significant indications in exploring the ultrafine nanoparticles for water splitting reaction,fuel cells and organic synthesis.(3)The Mott-Schottky heterojunction formed at the interface of ultrafine metallic Ni and semiconducting V2O3 nanoparticles was constructed,and the heterojunctions were“knitted”into the tulle-like monolayer nanosheets on nickel foam(NF).The greatly reduced particle sizes of both Ni and V2O3 on the Mott-Schottky heterojunction highly enhanced the number of Schottky heterojunctions per unit area of the materials.Moreover,arranging the heterojunctions into the monolayer nanosheets made the heterojunctions repeat and expose to the electrolyte sufficiently.The Schottky heterojunctions were like countless self-powered charge transfer workstations embedded in the tulle-like monolayer nanosheets,promoting maximum of the materials to participate into the electron transfer and become catalytic active sites.In addition,the tulle-like monolayer nanosheet structure can assist in pumping liquid phase electrolyte to the surface of catalysts,owing to the strong capillary force.The as-prepared V2O3/Ni/NF Mott-Schottky catalyst exhibited excellent HER performance with a low?10 of 54 m V and only needs-107 m V to get the current density of-100 m A cm^-2.Furthermore,V2O3/Ni/NF Schottky electrocatalyst exhibited excellent UOR activity:1.40,1.51 and 1.61 V versus reversible hydrogen electrode(RHE)voltage were required to reach a current density of 100,500 and 1000 m A cm^-2,respectively.(4)In this paper,the Ni₃V₂O₈ precursor was like a“seed”,and melamine was like“soil”providing the source of carbon and nitrogen,to“grow”vertical nitrogen doped carbon nanotube arrays on the carbon cloth fiber,using the method of phase separation.The VN/Ni heterojunction composite with nitrogen doped carbon nanotubes arrays(Ni/VN/N-CNTA@CC)were prepared,which was similar to the tube brush.The ultrasmall size VN/Ni heterojunction embedded on the nitrogen-doped carbon nanotubes was like building a“highway”for the continuous electron transfer,which accelerated the rapid electron transfer between the heterostructure and the carbon cloth to achieve excellent catalytic performance.In terms of morphology regulation,the vertically grown carbon nanotube array was like a needle,which was not conducive to the adhesion of bubbles,and accelerated the desorption of generated products,thus improving the performance of electrocatalysis.Thanks to the above advantages,the obtained Ni/VN/N-CNTA@CC catalyst has excellent HER and UOR performance.