Preparation Of Transition Metal Doped MoSe₂@C Nanofiber Membrane And Research On Performance Electrochemical Nitrogen Fixation

Ammonia occupies a large proportion in the national economy.Firstly,ammonia is mainly used for the production of ammonia-containing fertilizers in agriculture;in recent years,it has been considered as a potential transportation fuel for green energy.In addition,it is widely used in plastics,cosmetics,pharmaceuticals,and textiles.And other fields.Although about 78%of nitrogen is free in the air,it cannot be used directly by humans due to its chemical inertness and high bonding energy of N?N(940.95 k J mol^-1).The nitrogen fixation process currently used in industry is the Haber-Bosch method.Because it is carried out under high temperature and high pressure and Fe-based catalyst conditions,it needs to consume a huge amount of energy and produce CO₂ and other greenhouse gases.Therefore,it is of great research significance to develop a green and sustainable method to synthesize ammonia from nitrogen in nature.Electrochemical Nitrogen Reduction Reaction(NRR)has attracted much attention due to its advantages such as its ability to be carried out at room temperature,abundant sources of raw materials(hydrogen source can be from water),and simple equipment.So far,noble metals such as Au,Pt,and Ru have been proved to have high catalytic activity and selectivity when used as NRR catalysts,but their low abundance and high price limit their industrial applications.Recently,the research on electrochemical NRR catalysts has shifted from precious metal catalysts to transition metal catalysts,especially transition metal disulfide TMDs(such as Mo S₂,MoSe₂,WS₂,etc.)due to their high catalytic activity,layered structure,unique photoelectric properties and rare earths.The advantages of rich elements have attracted attention in the field of electrochemical nitrogen fixation.Since molybdenum and nitrogen have a strong binding capacity(this is the reason why nitrogen fixation in natural nitrogen fixation is achieved by nitrogenase using Mo-based active center),Mo-based NRR catalysts have received widespread attention,especially MoSe₂ has a lower the band gap and higher conductivity have good prospects for the research of NRR catalytic performance.However,the catalytic activity of molybdenum atoms is only exposed on the semi-open edges of MoSe₂,and it is hindered by negatively charged selenium atoms so that nitrogen atoms cannot approach its base surface,which will result in Faraday efficiency with lower ammonia yield.Most of the NRR catalysts studied so far exist in the state of powder and need to be coated on carbon cloth,carbon paper and foamed nickel with the aid of a binder.Therefore,the development of a self-supporting NRR catalyst with uniform structure,good catalytic activity and selectivity has important practical significance for promoting electrocatalytic NRR reactions.This article focuses on the controllable preparation of transition metal-doped MoSe₂ self-supporting catalysts and its application in electrocatalytic NRR performance.First,the carbon nanofiber membrane was prepared by electrospinning combined with post-processing.The carbon nanofiber membrane was used as the carrier of the NRR catalyst,and the material with nano petals uniformly supported on the carbon nanofibers was prepared by the hydrothermal synthesis method as the NRR catalyst.XRD,EPR,XPS and electrochemical performance was tested to explore the mechanism of electrochemical NRR.The main results of this paper include the following three aspects:(1)This article systematically discussed the influence of spinning solution parameters and electrospinning process parameters on the morphology of nanofiber membranes in the electrospinning process.After exploration,it is found that PAN nanofiber membranes are the most suitable spinning conditions at a concentration of 13 wt%,a spinning voltage of 30 k V,a spinning receiving distance of 25 cm,a temperature of 25±2°C and a humidity of 45±2%.Combined with the field emission electron microscope,the PAN nanofiber film with uniform nanostructure is selected to form a carbon nanofiber film through the process of pre-oxidation and carbonization.(2)Four kinds of Zr_yMo_1-ySe₂@C nanofiber membranes with different proportions were prepared by using carbon nanofiber membrane as the catalytic carrier and combined with hydrothermal synthesis method.Through field emission electron microscopy,it is found that different proportions of Zr-doped MoSe₂ can be evenly distributed on the carbon nanofiber membrane,preventing the formation of large-area agglomerated nanoflowers.The XRD characterization and analysis showed that the synthesized material was in line with the crystal structure of 2H-MoSe₂.The electrochemical performance test and analysis of the Zr_yMo_1-ySe₂@C nanofiber membrane with a self-supporting structure confirmed that the molar ratio of Zr to Mo is1:9,which has good electrocatalytic activity,which is the ammonia yield of-0.45 V vs.RHE is3.04×10^-10mol s^–1 cm^–2,and the Faraday efficiency is 21.61%in 0.1 M Na₂SO₄.(3)Prepare transition metal-doped MoSe₂@C(M-MoSe₂@C(M=Zr,W,Y))nanofiber membranes with the optimal doping ratio by hydrothermal synthesis.It can be seen intuitively from the apparent morphology that the doped catalyst and pure MoSe₂@C are uniformly distributed in petal nanostructures,and the transition metal doped MoSe₂@C creates obvious vacancy defects,which improves the catalytic activity and selection of the NRR catalyst The Zr-MoSe₂@C catalyst has a good ammonia yield of 3.04×10^-10mol s^–1 cm^–2at the optimal potential-0.45 V vs.RHE,a Faraday efficiency of 21.61%,and a good Long-term stability and reusability.