Preparation And Electrochemical Performance Of Three-dimensional Graphene Foam

New energy devices have attracted wide attention due to their environmental friendliness and sustainability.Under the current situation of environmental pollution and resource shortage,high-performance new energy devices are urgently needed.Among them,the key factor affecting battery performance is the electrode material.Graphene has been widely used in batteries because of its high conductivity and large specific surface area.However,two-dimensional graphene nanosheets are prone to irreversible agglomeration due to van der Waals force and contact resistance,which reduces battery performance.On the contrary,the three-dimensional graphene foam has high conductivity and large specific surface area of graphene,and also has a stable three-dimensional interconnected porous structure,which can provide ion transport channels and active sites for electrochemical reactions.Therefore,this paper designs and prepares three-dimensional graphene foam materials,which are used in the electrochemical field.First of all,the nickel foam as the base material,through the chemical vapor deposition method to prepare graphene foam;then Fe₃O₄ nanoparticles are used as the catalyst,After the second chemical vapor deposition,carbon nanotubes are grown on the surface of the graphene foam to obtain carbon nanotubes@Graphene Foam（CNTs@Graphene Foam,CGF）.This paper systematically studied the influence of temperature,time,catalyst carrier,gas pressure and other factors during the growth of CNTs on the surface of CGF.The study found that Fe₃O₄ nanoparticles were used as a catalyst,the growth temperature was 750℃,and the growth time was 20 min,the quality of CNTs was the best.Through the inspection of the morphology and structure of CGF,it is found that the degree of graphitization is high,the defects are few,and the carbon nanotubes grow vertically and uniformly on the surface of the graphene foam,forming a good connection conductive layer.Then,using CGF as the base material,Mn₃O₄ nanosheets are grown on the surface of CGF by electrochemical deposition,and then modified by inserting Na⁺in the Mn₃O₄-CGF through CV cycle to obtain NaMnO₂-CGF.This paper systematically studied the electrochemical modification mechanism:analyzed the effect of Na⁺insertion;determined the minimum voltage required for Na⁺insertion:1.2 V;and analyzed the effect of Na⁺insertion under different oxidation voltages,and finally found that it is 1.4V to insert Na⁺,it has the best electrochemical performance.At the same time,this article analyzes the role of CNTs in the electrode:reducing the electrode resistance,connecting the conductive layer and the catalytic layer,and improving the electrochemical conversion efficiency;the study found that Under the oxidation voltage 1.4 V,a current density of 1 A g^-1,NaMnO₂-CGF has a capacity of 343.5 F g^-1,and after 5000 cycles at a current density of 10 A g^-1,the capacity retention rate is 74.4%.Finally,this article uses Ni foam as the substrate and graphene nano-ribbons（GNRs）as the toughening agent to prepare graphene nanoribbons@Graphene Foam（GNRs@Graphene Foam,GGF）by chemical vapor deposition.Subsequently,Co Fe₂O₄,Fe₃O₄ nanoparticles were used as metal catalysts,and polydopamine was used as a nitrogen doping agent to prepare Co Fe₂O₄-N-GGF,Fe₃O₄-N-GGF,N-GGF composite materials and their electrocatalytic properties were studied.Through the detection of its electrocatalytic performance,oxygen reduction reaction（ORR）and oxygen evolution reaction（OER）,it is found that the bimetallic catalytic system Co Fe₂O₄-N-GGF has the best catalytic effect.At the same time,the results are verified through simulation calculations,and it is found that the electron transfer number of Co Fe₂O₄-N-GGF is n=3.93,which is the closest to the ideal 4-electron system.