Controllable Preparation And Electrocatalytic Properties Of Carbon Fiber Supported Transition Metal Composite Electrode Materials

In recent years,due to the increasing environment and energy problems,various types of new energy sources need to be developed to reduce the demand for traditional fossil energy sources.However,fuel cells have been widely studied for their high energy conversion and non-polluting advantages,the oxygen reduction reaction（ORR）as the core reaction in the energy conversion system,has a decisive impact on its wide range of applications,so it is important to develop low-cost,high-activity oxygen reduction catalysts for energy systems.At present,platinum-based catalysts are still the most effective catalysts for ORR,but the disadvantages of platinum-based catalysts,such as easy poisoning and poor stability,are not conducive to long-term development,and the storage capacity of platinum limits its practical application.Therefore,the preparation of alloys reduces the amount of precious metals and improves the catalytic performance at the same time.Hydrogen energy is also a hot topic in the energy field due to its high energy density and zero pollution emissions.Water-splitting reaction is a relatively simple method for hydrogen production,which increases the energy conversion rate by reducing the overpotential.Platinum-based catalysts also have good catalytic activity for hydrogen precipitation reactions（HER）.However,its application is also limited by its scarcity and high price.Therefore,it is of great significance to develop non-noble metal catalysts with high activity and good stability for hydrogen production.Since the electronic structure of molybdenum is similar to platinum group metals,a lot of effort has been devoted to the study of molybdenum-based highly active compounds in recent years.In this paper,carbon nanofibers prepared by electrospinning are used as carriers,and a series of composites are prepared by solvothermal and high temperature carbonization method for ORR and HER.The main work is divided into the following three parts:1.A series of composites are prepared by electrospinning and subsequent high-temperature carbonization process,the effects of carbonization temperature and different components for ORR catalytic performance were studied.The results show that the two-component of Pt and Fe coexist,the best ORR performance at the carbonization temperature of 900℃（Fe-Pt/CNFs-900）for the 4e^-transfer process,where the onset potential is 0.99V,the half-wave potential is 0.79V,and the limiting current density reaches 6.0mAcm^-2.After 5000CV cycles,comparing the LSV curves before and after the cycles Fe-Pt/CNFs-900,where no significant decrease,while the LSV curve of Pt/C obviously shifted toward the low potential,Fe-Pt/CNFs-900 had good cycling stability.2.Nitrogen-doped Mo-based composites were prepared by the solvoethermal method and high-temperature carbonization method using pre-oxidized fiber membranes as templates.HER tests is carried out for different carbonization temperatures and whether nitrogen doping,it is found that the best hydrogen evolution performance is achieved at the nitrogen-doped carbonization temperature of 900℃（N-M-9）,with an overpotential of 119mV,the Tafel slope of 106.9mV dec^-1,the electrochemical active surface area of 35.3mFcm^-2,with minimum impedance and good stability.3.Based on the above experiments,the Co,S co-doped Mo-based composites were prepared,the doping amount of metallic cobalt was 0.03mmol,in the carbonization process the structure formed when secondary sulfidation was carried out was MoS₂-Co_1-xS（Mo-Co-S-3）.The overpotential of Mo-Co-S-3 at a current density of 10mAcm^-2is 139mV,the Tafel slope is 74.7mV dec^-1,and the electrochemical active surface area is 10.55mFcm^-2.After 28h of i-t test,which no significant increase in potential and the cycling stability was good.