| In recent years,due to the severe environmental crisis and global warming caused by the massive consumption of fossil fuels,hydrogen,as a clean energy with high energy density and combustion product of water,is expected to become an ideal substitute for fossil fuels.Electrocatalytic water splitting to produce hydrogen is an effective way to obtain hydrogen,which includes hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.At present,noble metal Pt-based materials are the most efficient electrocatalysts for the hydrogen evolution reaction,and Ru/Ir-based materials are the most efficient electrocatalysts for the oxygen evolution reaction.However,the low reserves and high prices of noble metals greatly limit their large-scale commercial application.Metal organic frameworks（MOF）have attracted extensive attention due to their unique spatial structure,large specific surface area,and tunable porosity,and they are currently one of the ideal materials to replace noble metals.Based on this,this thesis is based on metal organic frameworks（MOF）derived cobalt-nitrogen-carbon catalysts,and the electrocatalytic performance of non-noble metal materials is improved by controlling the calcination temperature,the molar percentage of doping metal,and the doping metal species.MOF-derived AT-Co-N/C-800 materials were synthesized by co-precipitation,high-temperature carbonization and HF etching,and the effects of different calcination temperatures on the morphology and properties of the products were investigated.Introducing a silicon source when synthesizing the precursor can expose more voids in the material after etching,thereby significantly increasing the contact area between the catalyst and the electrolyte.The electrochemical test results show that the appropriate calcination temperature can greatly improve the catalytic performance and show good hydrogen evolution performance and oxygen evolution performance under alkaline conditions.123 m V and 240m V were required to reach a current density of 10 m A·cm-2,the corresponding Tafel slopes are 215 m V dec-1 and 130 m V dec-1.To further explore the effect of cobalt content on the electrocatalytic performance,a series of Co-ZIF-8-x were synthesized by adjusting the molar ratio of cobalt to zinc（x represents the molar percentage of Coin the total metal）.Since the boiling point of Zn is907°C,the evaporation of Zn atoms after high temperature calcination at 950°C will have a sequestering effect on Coatoms,and then Cosingle-atom catalyst（CoSAs-N/C-3）is synthesized.The test results demonstrate that the single atom dispersed Cohas high metal atom utilization,and CoSAs-N/C-3 has excellent electrocatalytic performance under both alkaline and acidic conditions compared with metal nanoparticles.In overall water splitting test,CoSAs-N/C-3 can reach a current density of 10 m A cm-2 with only an applied voltage of1.74 V.In order to further explore the effect of doping metal species on the electrocatalytic performance,the metal doping species are added on the basis of the previous chapter.CoFe-ZIF-8 was prepared by co-precipitation method,and then cobalt-iron-nitrogen-carbon catalyst（CoFe-N/C）was synthesized by high-temperature calcination method.The interaction between cobalt-iron bimetals enhances the electrical conductivity of the material to improve the electrocatalytic performance of the material,and the framework structure of the MOF also provides an effective transport path for electrons.In conclusion,the HER overpotential required for the CoFe-N/C material to generate a current density of 10 m A cm-2 in an acidic medium is 76 m V,and the Tafel slope is 98 m V dec-1. |
PDF Full Text Request