Properties Of Carbon Nanosphere-based Composites As Bifunctional Oxygen Catalysts

With the continuous growth of global carbon emissions,the increasing difficulty of controlling temperature increase,and the increasingly acute problem of resource shortages such as fossil fuels,the crisis hidden under the surface of the benefits brought by fossil energy is becoming more and more difficult to ignore.According to the forecast of the international energy market put forward by the U.S.Energy Information Administration(EIA)in the International Energy Outlook(IEO)in 2020,by 2050,half of the world's energy consumption will be occupied by Asia,and its growth rate will exceed that of the world.On any other area.In addition,between 2019 and 2050,driven by economic growth and increased income,the region's power generation will more than double.Therefore,electrochemical energy conversion and storage devices that decompose water into hydrogen and oxygen in the form of chemical bonds to store light or electrical energy are particularly popular among many clean energy technologies as high-efficiency,low-cost,clean and sustainable energy conversion and storage systems.Eye-catching.Based on the rich reserves of advanced functional carbon materials on the earth and their excellent performance in the oxygen reduction and oxygen evolution reactions(ORR/OER)that determine the rate of electrochemical reactions,this thesis selects nano carbon spheres(NCS)for modification and optimization.In order to achieve the goal of making it an excellent dual-function catalyst.This article aims to synthesize carbon nanosphere-based composites with excellent dual-functional electrocatalytic performance and explore its catalytic mechanism as the research goal.Using carbon nanospheres as the precursor,the template pretreatment method,reaction medium and other conditions are changed.Two bifunctional oxygen electrocatalysts(Co₃O₄@Z67/NCS-T and Mn Co₂O₄/NCS-T)that perform well under alkaline conditions were prepared,and then the morphology and catalytic mechanism of composite materials were studied and deduced.A large number of characterization methods and electrochemical performance test methods are used to analyze the microstructure,element distribution,crystal composition,wettability,and electron transfer efficiency of the material.The research content is as follows:Using polyvinylpyrrolidone as a binder,the nitrogen-doped carbon nanospheres are compounded with ZIF-67 as the precursor,and the carbonization temperature is set to700-900?(every 50?)for high temperature carbonization.The obtained Co₃O₄@Z67/NCS-T composite material was found to be supported by nano-carbon spheres after characterization and testing.The material has relatively good dispersibility and large specific surface area,and exhibits excellent dual-function electrical properties in alkaline media.Catalytic(ORR/OER)activity(?E=E _j=10(1.55)-E_1/2(0.812)=0.738V).The large limiting current density(6.83 m A cm^-2)and positive half-wave potential(0.812V)of Co₃O₄@Z67/NCS-850 in ORR can be attributed to the existence of Co²⁺between NCS and Co₃O₄crystals Synergy.A large number of oxygen vacancies widely existing on the surface of the carbonized carbon material can enhance the adsorption strength on the O₂ interface,and activate the adsorbed O₂ to O₂^-in the reaction,which alleviates the limitation of O scarcity on ORR,so that the ORR activity can be obtained.improve.During OER,Co₃O₄@Z67/NCS-850 showed a lower overpotential(320m V)when the current density was 10 m A cm^-2,and the Faraday efficiency was 90.09%.The high conductivity of the composite material given by the carbon material and the enhanced oxygen storage and output capacity of the material due to the unique pore size of the carbon material,the charge transfer during the reaction,and the highly active substance(OOH*)that can promote the OER reaction Generation and smooth transportation are greatly facilitated.In this study,providing sufficient electrochemically active sites for the ORR/OER process comes from the interaction between NCS and Co₃O₄(Co³⁺/Co²⁺).In addition,we use a simple hydrothermal method to uniformly grow cobalt-manganese oxide nanosheets on the surface of NCS,and then carbonize with temperature as a variable(400,450,500,550,and 600°C)to obtain a unique structure of Mn Co₂O₄/NCS-T composite material(550?is the best).The catalyst has a beautiful and strong nano-flower cluster morphology,and the combination of the body of the carbon material and the sheet metal oxide makes the composite have a porous structure and a large specific surface area.In the ORR reaction process,Mn Co₂O₄/NCS-T stands out among similar catalysts(peak value is 0.83 V vs.RHE).Due to the synergy between metal(Mn²⁺,Co²⁺)ions and the use of carbon spheres as a substrate,the transfer rate of charge and O₂ is improved.Thus,the ORR reaction is completed efficiently and stably.For the OER part,when the rated current is set to 10m A·cm^-2,the overpotential of Mn Co₂O₄/NCS-550 presents a lower 350m V,and the higher Faraday efficiency is(92.7%).The strong interaction between Co OOH(Co³⁺)and oxygen vacancies promotes the production of O₂,and its unique structure facilitates the escape of O₂,promotes the reaction,and proves its superiority in the ORR/OER process?activity.In this paper,a composite material for bifunctional(ORR/OER)catalysis under alkaline conditions with a 3D porous structure prepared by the composite of metal/metal oxide and nano-carbon spheres is used.The characterization and electrochemical tests show that it is in alleviating the energy crisis.The potential value of such catalysts in the field of electrocatalysis.