Preparation And Electrocatalytic Performance Of Metal-Organic Framework Materials And Their Derivatives

Energy and the environment have always been the long-standing issues for human survival.In today's society,most of the energy we rely on for living is still the combustion of fossil fuels?such as coal,oil?,etc.Although this has provided great convenience to our lives,the products of its combustion cause serious environment pollutions,such as PM2.5 particles infecting the human respiratory tract,corrosion of buildings caused by acid rain,the melting of glaciers caused by global warming,resulting in rising sea levels and reduced land area,etc.Not only that,with the start of the Industrial Revolution and the surge in population,the current reserves of fossil fuels on earth have fallen sharply or even become scarce.Therefore,the development of new sustainable green energy is urgent.Although in the current exploration and development,the use of clean energy such as wind energy and solar energy has been gradually established,these energy sources have intermittent shortcomings.Therefore,it is necessary to convert these energy sources into stable chemical energy for effective energy storage and utilization.In the conversion between these energy sources and chemical and electrical energy,catalysts play a vital role.Oxygen reduction reaction?ORR?is an important reaction in fuel cells and metal-air batteries.It is currently facing the kinetic problem of slow cathode reaction.Therefore,the search for catalysts dedicated to improve this reaction kinetics has been of great interest.Precious metal catalysts?such as Pt/C?that have been put into the commercial use at present have is of difficulty in actual production and large-scale applications due to the complexity in mining the precious metals and the shortage of the earth,and high production costs as well.Electrocatalytic stability also is an issue that makes the recycle of the catalyst material for multiple uses difficult.This requires the exploration and research of non-precious metal catalysts or metal-free catalysts.In this paper,we successfully synthesized five new homogeneous bimetallic ZIF precursors?ZnCo-JUC160?with different Zn/Co ratios,and derived a series of N-doped porous carbons embedded with Co nanoparticles.This kind of catalyst derived from ZIF not only has high electrical conductivity,but also expose more active site of non-noble metals to improve the reaction kinetics.Therefore,we systematically studied the effect of different bimetal ratios on the electrocatalytic performance of the obtained porous carbon catalysts by ZIF precursors.Among them,the optimized Zn₂Co₁-NPs@NC sample shows excellent ORR performance.The half-wave potential(E_1/2)is 0.849 V,which is better than the commercial Pt/C.The electron transfer number is 3.98 at 0.2 V to 0.5 V,showing nearly four-electron selectivity.In addition,the long-term stability of the Zn₂Co₁-NPs@NC sample was far better than that of the commercial Pt/C by exploring the current–time chronoamperometric response over 40 000 s.This work encourages us to continue to explore new ZIFs for sustainable energy development.The electrochemical oxygen evolution reaction?OER?is an important semi-reaction in the entire electrochemical splitting water.Because the reaction process involves in the problem of slow kinetics caused by a multi-step proton coupling,a large overpotential is required to achieve the highly rapid reaction.The catalyst searching and design for this reaction has become the focus of current research.At present,the research of catalyst on this reaction is well-developed in noble metal catalysts?such as RuO₂,IrO₂?,but it still faces the key issue of shortcomings as the lack of earth resources.MOFs have become the most potential candidates of non-noble catalyst materials due to their high specific surface area and porosity,controllable structure,and ease of functionalization.In this thesis,new Fe-MOF crystals were successfully synthesized and in situ grown on nickel foam to obtain two-dimensional Fe-MOF nanosheets.Such in-situ MOF nanosheets not only expose more catalytically active sites,but also reduce the energy barrier in the catalytic process.Among them,the Fe-MOF/NF electrode exhibits excellent OER catalytic performance,with an overpotential of 230mV and a Tafel slope of22.48mV dec^-1 at a current density of 10mA cm^-2.In addition,the catalyst also showed excellent catalytic stability,with only slight degradation in catalytic performance after 2,000^th CV cycles.This work will stimulate the investigation of new MOFs with high catalytic activity and stability.