Study On Structural Regulation And Electrocatalytic Properties Of Rare Earth Modified Spinel

In order to solve the problem of environmental pollution and energy crisis caused by excessive consumption of traditional fossil fuels,the development of environmental protection and efficient energy technology has become the most of important topics.As a promising green solution,water electrolysis hydrogen production has attracted extensive attention,however,its efficiency is greatly limited by the slow kinetics of anodic oxygen evolution reaction（OER）.Spinel type binary transition metal oxides represent a kind of promising catalysts for oxygen evolution reaction because of their low toxicity,high abundance,excellent stability and rich redox properties.There also have been many attempts to use rare earths in electrocatalytic reactions.The combination of rare earth and transition metal oxides can effectively regulate the electronic and crystal structure,the interaction between the active species and the substrate,and the surface properties of the catalyst,thus improving the catalytic activity and stability of the main electrocatalyst.In this thesis,firstly the spinel-structured Cu Co₂O₄ was prepared by a sol-gel method,X-ray diffraction and transmission electron microscopy showed that Cu O segregation layer was generated on the surface of the material.In the synthesis stage,the rare earth Eu element was added to obtain Cu Eu_xCo_2-xO₄,rare earth doped can reduce the grain boundary of spinel,inhibition of grain growth,control A bit segregation in the electrochemical cycle at the same time have the effect of supporting lattice,transmission electron microscopy（TEM）observation results support this conclusion,the product of new synthetic potential drop to 330 m V.Secondly,spinel-structured Co Fe₂O₄ was selected as the research object,and rare earth Eu was selected as the doping element according to the parameters of ion radius and electronegativity.The spinel Co Eu_xFe_2-xO₄ was also prepared by a sol-gel method,part of Eu and B site Fe generated Eu Fe O₃.Fe consumption at site B promotes surface defects and oxygen vacancies,exposing cobalt sites and promoting surface remodeling.They are transformed into Co ions in octahedral center as the active center of electrocatalytic OER.In the performance test of electrocatalytic oxygen precipitation reaction,the overpotential at 10 m A·cm^-2 is 305 m V,which is about 45 m V lower than that before the doping of Eu,showing good electrocatalytic performance.Finally,spinel-structured Co Fe₂O₄ with abundant oxygen vacancy was designed and synthesized.Electron paramagnetic resonance（EPR）lines showed that the sample surface had abundant defects.Oxygen vacancies may be destroyed in the high oxidation condition of electrocatalytic OER,resulting in rapid degradation of their properties in the long-term OER stability test.In order to stabilize the oxygen vacancy,it is a feasible strategy to compensate the coordination number of metal elements by filling with non-metallic elements with different atomic radii and electronegativity.Sulfur atoms can not only effectively stabilize the oxygen vacancy under the condition of high oxidation of OER,but also form cobalt-sulfur coordination with the cobalt active center next to the oxygen vacancy,thus regulating the electronic structure of the active center and increasing the adsorption energy of H₂O on the cobalt active site.After electrocatalytic oxygen precipitation reaction test,sulfur modified products have better catalytic performance and better stability.This thesis is intended to control the preparation of spinel binary transition metal oxides,and through doping the different elements to conduct a series of performance control research,at the same time with the help of electron microscope and spectroscopic characterization methods to explore the material of the relationship between the structure and performance of regulation,and the electric catalytic OER research on its application value,the results provide guidance and ideas for optimizing the catalytic properties and activity of spinel type binary transition metal oxides as electrocatalysts.