Design And Synthesis Of Transition Metal Oxide/V₂CT_x Composite And Its Electrocatalytic Oxygen Evolution Performance

As the resource supply of fossil energy becomes increasingly scarce and global warming intensifies,there is an urgent need to develop alternative green and sustainable energy conversion and storage technologies,such as batteries,fuel cells and electrocatalytic water decomposition.As a key reaction in secondary metal-air batteries and electrocatalytic water decomposition,electrocatalytic oxygen evolution（OER）plays an important role in the efficiency and operational stability of these energy conversion devices.Among them,high activity electrocatalyst is very important to improve the slow OER reaction kinetics,obtain low overpotential and excellent catalytic stability.However,the most efficient catalysts currently available,RuO₂ and IrO₂,are limited in their widespread use due to their poor durability,scarcity,and high cost.Therefore,non-noble metal OER catalysts with low development cost,high electrochemical activity and good stability are very necessary.In order to obtain low-cost and abundant non-precious metal electrocatalysts,many studies have been conducted,such as transition metal oxides,which have relatively low overpotential,good electrocatalytic stability and activity,and can be candidate materials for OER electrocatalysts.Among them,Fe₂O₃ and iron and cobalt spinel have the advantages of abundant reserves,low cost,strong oxidation reduction and good stability,which have attracted the attention of scholars.However,the poor conductivity of transition metal oxides and insufficient exposure of active sites limit their electrocatalytic activity.Layered two-dimensional transition metal carbides or nitride compounds（2D MXenes）have both good metal conductivity,excellent hydrophilicity and high specific surface area.By combining MXenes with transition metal oxides,they can effectively compensate for their shortcomings.Based on this,this paper combined transition metal oxides with MXenes,and studied their OER performance,the specific content is as follows:Part Ⅰ:The mechanism of OER reaction,the research progress of spinel and other transition metal oxides and MXenes in the field of OER are reviewed.The synthesis methods of transition metal oxides and MXenes are summarized.Finally,the research content and the basis of the topic selection of this paper are introduced.Part Ⅱ:The reagents,instruments and characterization methods used in the paper are described.Part Ⅲ:Fe₂O₃/V₂CT_x/NF composite catalysts were prepared by solvothermal method by in-situ growingFe₂O₃/V₂CT_x composite on nickel foam substrate,and their OER properties were studied.When the current density ofFe₂O₃/V₂CT_x/NF is 10 mA cm^-2,the overpotential is271 mV,72 mV lower than that of the originalFe₂O₃/NF（343 mV）catalyst.In addition,the Tafel slope ofFe₂O₃/V₂CT_x/NF catalyst is as low as 51.5mV dec^-1,the double layer capacitance value(C_dl)is 7.3 m F cm^-2,and the catalyst remains stable for 90h.These excellent properties are due to the introduction of V₂CT_x,which improves the conductivity of the composites.In addition,the formation of the heterogeneous interface betweenFe₂O₃ and V₂CT_x accelerates the electron transfer between the two phases,thus improving the overall reactivity.Part Ⅳ:NiCo₂O₄/V₂CT_x composites are grown in situ on nickel foam using a simple two-step synthesis scheme.The addition of V₂CT_x changes the morphology of NiCo₂O₄ from the original nanoneedles to nanosheets,and grows vertically or inclinately on the surface of V₂CT_x.In addition,the presence of V₂CT_x nanosheets can also accelerate the interfacial electron transport performance,thus giving NiCo₂O₄/V₂CT_x/NF electrocatalysts enhanced conductivity,abundant active sites and shortened charge transfer path,greatly improving the electrocatalytic activity.Finally,in 1 M KOH electrolyte,at the current density of 10 mA cm^-2,the overpotential is 266 mV,and after the measurement of chronopotentiometry,the stability can be maintained for 800h.Part Ⅴ:The composite of iron spinel and MXene was synthesized by solvothermal method and grown on nickel foam in situ.The effect of MXene on the OER performance of spinel was studied.Taking CoFe₂O₄ as an example,compared with the original CoFe₂O₄/NF,CoFe₂O₄/V₂CT_x/NF catalyst has higher OER performance,and the overpotential of CoFe₂O₄/V₂CT_x/NF catalyst is 249 mV at current density of 10 mA cm^-2.The durability of the catalyst was measured by chronopotentiometry,and it was found that the stability of 1100h was still maintained at different current densities.In addition,NiFe₂O₄/NF,MnFe₂O₄/NF,CuFe₂O₄/NF and their composite catalysts were prepared in order to further confirm the improvement of OER performance of spinel by MXene.Through the detailed electrocatalytic performance test of these composites,it is found that the composites have better OER activity.Moreover,through characterization analysis,we found that anchoring spinel nanoparticles on the surface of MXene nanosheets can effectively reduce particle aggregation,which is conducive to exposing more active sites.In addition,the formation of a strong interface between MXene and spinel shortened the charge transfer path,promoted the charge transfer from spinel to MXene,and enhanced the conductivity and reactivity of the catalyst.Part Ⅵ:The thesis work is summarized and prospected.