Synthesis Of Nickel-Cobalt-based Catalysts And Their Catalytic Performance For Electrooxidation

At present,the main source of global energy supply is fossil fuels.This non-renewable energy not only pollutes the environment,but also has limited storage.Therefore,the development of clean energy is imminent.At present,hydrogen has become one of the energy sources,and countries around the world are competing for development.Among them,hydrogen production by electrolysis of water is a hydrogen production technology with great potential.Among them,hydrogen evolution（HER）and oxygen evolution reaction（OER）are the two half-reactions of the electrolysis of water to produce hydrogen.In the process of water electrolysis,the oxygen evolution reaction（OER,4OH^-→2H₂O+O₂+4e^-）requires a higher thermodynamic energy barrier in the process of O-H bond breakage and O=O bond formation,which is the speed-determining step of water electrolysis.Theoretically,under standard conditions,electrolyzed water requires a voltage of 1.23 V,but under actual operating conditions,the voltage may even reach 1.5 V.The urea oxidation reaction（UOR）requires a theoretical electrolysis voltage lower than OER.While the anode degrades urea-rich wastewater,the cathode is accompanied by the generation of hydrogen,and the theoretical value of the energy consumption of hydrogen production by electrolysis is lower than that of pure water electrolysis.Therefore,this thesis aims to reduce the total energy consumption of electrolyzed water by preparing cheap and easily available transition metal catalysts for OER and replacing OER with urea oxidation reaction（UOR）,thereby reducing the thermodynamic energy barrier and achieving the purpose of accelerating the progress of the hydrogen evolution reaction.In addition,noble metal oxides such as IrO₂ and RuO₂ are the most active OER electrocatalysts.Due to their low crust reserves and high prices,which seriously hinder their large-scale commercialization.Therefore,the development of non-precious metal materials is the focus of current electrocatalyst research.In this paper,a series of Ni-based and Co-based electrocatalysts have been prepared based on the relatively abundant reserves of Ni and Co in the earth’s crust.The main research contents are as follows:（1）Phytic acid（PA）is a unique biomass material.Because it contains 6 phosphate groups,it is an organic acid with a good ability to chelate metal ions,and it is environmentally friendly.At room temperature,using a simple mechanical stirring method,and through using phytic acid as raw material,adding different metal salts to make a complex reaction,cobalt phytate（PA-Co）,nickel phytate（PA-Ni）and copper phytate（PA-Cu）were prepared respectively.Compared with PA-Ni and PA-Cu,PA-Co exhibits better OER catalytic performance.When the current density is 10 m A cm^-2,the OER overpotential is 360 m V,and the Tafel slope is 57.2 m V dec^-1.In order to further improve the electrocatalytic performance of PA-Co,the material has been subjected to high-temperature treatment under different temperatures in the N₂atmosphere.The results show that PA-Co-400 exhibits more excellent electrocatalytic performance.When the current density is 10 m A cm^-2,the OER overpotential is 320m V,the Tafel slope is 53 m V dec^-1,and after the V-T stability test for 80 h,the overpotential does not increase significantly.It is proved that PA-Co-400 has excellent OER catalytic activity and stability.（2）Preparation of Zn/Ni-MOF powder by a simple solvothermal method,and then add pyrrole and oxidant FeCl₃ under stirring at room temperature to obtain Zn/Ni-MOF@PPy composite material.Furthermore,by adding different content of oxidant FeCl₃,the effect of it on the catalytic performance of Zn/Ni-MOF@PPy composite material was studied.The results show that the Zn/Ni-MOF@PPy-1 composite has excellent OER catalytic performance in 1 M KOH.When the current density is 10 m A cm^-2,the OER overpotential is 300 m V,the Tafel slope is 43.4 m V dec^-1,and after 24h of V-T stability test,the overpotential does not increase significantly,which proves that Zn/Ni-MOF@PPy composite material has excellent OER activity and stability.The above-mentioned excellent performance is attributed to the higher specific surface area of Ni-MOF and the higher specific capacity and good conductivity of polypyrrole（PPy）.（3）Preparation of CuO-Ni（OH）₂ electrocatalyst for UOR under alkaline conditions.By a simple etching method,using Cu₂O as template and S₂O₃^2-as an etchant,a series of CuO-Ni（OH）₂ composite materials were synthesized.Under the condition of 1 M KOH+0.33 M Urea,the urea electrooxidation performance of CuO-Ni（OH）₂ composite material was tested,and commercial Ni（OH）₂ was used as a control catalyst.After the 36 h I-T stability test,the current density did not decrease significantly,indicating that the CuO-Ni（OH）₂-d composite is an efficient and stable UOR electrocatalyst.