Study On Synthesis And Catalytic Electrolysis Of Water Of MOFs Derivatives

With the increasingly serious energy crisis and environmental pollution,it is urgent to seek sustainable green energy.As a clean and sustainable way of producing hydrogen,water-splitting reaction has attracted wide attention from researchers.However,the commercial catalyst for hydrogen evolution reaction has low abundance and high cost,so it cannot be used on a large scale.Therefore,the development of low cost and high performance electrocatalyst has become a research trend in recent years.Low-cost and rich transition metal with excellent performance have achieved unprecedented development in the field of electrolysis of water.Ni and Co in transition metals have high abundance in the crust and excellent catalytic performance,which is favored by researchers.As a new functional material,the carbon composites derived from metal organic frameworks（MOFs）not only contain active metal nanoparticles,but also have the advantages of porosity,large specific surface area,uniform distribution of active sites,good stability,and good conductivity,which are widely used in catalytic electrolysis of water.In this thesis,simple and efficient hydrothermal method and high temperature thermal reduction method are used to conduct thermal reduction and doping treatment for different MOFs.Meanwhile,nitrogen-containing graphene is compounded to improve its electrocatalytic performance.The specific contents include:（1）2D Ni@C nanosheets are prepared by carbonization of 2D MOFs DUT-8（Ni）at high temperature.Comparing the properties of the composites at different carbonization temperatures,it is found that DUT-8（Ni）do not completely decompose at low temperatures,the crystallinity of Ni nanoparticles（Ni NPs）is low,and the electrocatalytic performance of the composites are poor.With the increase of carbonization temperature,DUT-8（Ni）completely decomposes,the crystallinity of Ni NPs gradually increases,and the electrocatalytic performance is also improved.However,when the carbonization temperature is 800℃,the electrochemical surface area of the composite decreases,and the electrocatalytic performance slightly decreases.Therefore,the 2D Ni@C obtained by carbonization at 700℃exhibits good electrocatalytic performance.When the current density in an alkaline solution is 10 mA cm^-2,the overpotential is 190 mV and the Tafel slope is 116.1 mV dec^-1.The good performance is due to the uniformity of Ni NPs embedded on the two-dimensional carbon nanosheets,which can effectively prevent particle agglomeration.At the same time,the carbon nanosheet matrix has good electrical conductivity.（2）Co-NC and Co-NC@N-rGO catalysts are obtained by heat-treating ZIF-67 and ZIF-67@DAE-GO.By recombination N-rGO,the conductivity of the composite can be improved.At the same time,the agglomeration of nanoparticles after pyrolysis also be reduced,more active sites can be exposed.The ratio of pyridine nitrogen in Co-NC@N-rGO is higher than Co-NC,which is more conducive to the occurrence of hydrogen evolution in electrolysis of water.When the current density of Co-NC@N-rGO and Co-NC catalysts in the acid electrolyte is 10 mA cm^-2,the hydrogen evolution overpotentials are 72 mV and 98 mV,respectively.When the overpotential reaches 600 mV,the maximum current densities reaches 1871 mA cm^-2and 1190 mA cm^-2.Their Tafel slopes are 88.6 mV dec^-1 and 94.5 mV dec^-1,respectively.In addition,the two catalysts can perform electrocatalytic hydrogen evolution reaction and electrocatalytic oxygen evolution reaction in alkaline electrolyte,and they are excellent dual-functional electrocatalysts.（3）CoNi-NC@N-rGO and CoNi-NC bimetallic catalysts are prepared by doping Ni in the process of preparing ZIF-67,followed by high temperature heat treatment.The experimental results show that the CoNi-NC@N-rGO catalyst has excellent hydrogen evolution catalytic performance under acidic conditions.When the current density is 10mA cm^-2,the overpotential is 78 mV.When the overpotential reaches 600 mV,the maximum current density reaches 2245 mA cm^-2.The Tafel slope is 85.6 mV dec^-1.In addition,in the alkaline electrolyte,CoNi-NC@N-rGO,as a bifunctional catalyst,has shown good hydrogen evolution and oxygen evolution catalytic performance.