Irradiation Control Of CoFe₂O₄ Thin Film Defects And OER Catalytic Performance

Electrochemical water splitting is currently one of the most promising technologies for large-scale energy storage.With the further development of this technology,the performance of the catalyst for oxygen evolution reaction is also raised.Among several catalyst systems,spinel-type transition metal oxides which are cheap?high durability and conductivity have become import candidate materials for OER catalysis.And how to improve the activity of spinel catalysts is currently a research hotspot.At present,the most representative method for controlling the activity of the catalyst is the regulation of oxygen defect.This method reduces the reaction potential by controlling the content of defects,but it still cannot quantify the content of oxygen defects,and cannot optimize the performance of the catalyst.For this problem,this paper proposes and confirms a regulation method.That is,the use of ultraviolet laser irradiation quantitatively controls the surface defects and microstructure of the spinel catalyst CoFe₂O₄.Change its electronic energy band structure and improve its OER catalytic activity.First,this article uses a pulsed laser deposition system?PLD?to prepare a pure phase CoFe₂O₄ thin films,we perform ultraviolet laser irradiation on the sample surface.According to the treatment,by controlling the laser pulse energy,pulse frequency,pulse number and other parameters to effectively achieve the regulation of the surface oxygen defect content.Using the sample with irradiation treatment as a catalyst,we have found that the potential of OER exhibits a volcano shape as a function of the irradiation time.Combining with the test results of oxygen defect content on the surface and surface morphology of the sample,we conducted detailed analysis and discussion.The content of the paper is as follows:The first chapter mainly introduces the research progress of electrocatalytic water splitting and OER,as well as related theories and experimental methods.First,we give the reaction mechanism of the electrocatalytic oxygen evolution reaction and several factors affecting the reaction efficiency,and describe the measurement standard of the reaction efficiency.Second,we introduce the research progress of the crystal structure and catalytic properties of spinel-type transition metal oxides for OER catalysis.After that,we explain the effect of oxygen defect regulation on the activity of the catalyst and the progress of the methods for the regulation of defects by light irradiation.Finally,the research content and methods of this paper were introduced.The second chapter mainly introduces the preparation and structural characterization of CoFe₂O₄ thin films.First of all,we introduce the working principle of the PLD used in the thin film manufacturing technology,and the control method and operation details of the experimental parameters in the preparation of the CoFe₂O₄ thin films by the PLD,including the preliminary target preparation steps.Second,we describe in detail the experimental process and operation steps of the ultraviolet laser irradiation method applied in this paper.Then the characterization technology of the structure and properties of the CoFe₂O₄ thin films were introduced.The change of surface topography of the sample was observed by AFM and SEM.The structure information of sample was analyzed by XRD.The electronic structure information of the sample surface was analyzed by XPS and synchrotron radiation XAS.Finally,the OER catalytic activity of the sample was characterized by an electrochemical workstation.In the third chapter,the experimental characterization results were listed in detail,and laser irradiation was applied to control the defects of CoFe₂O₄ thin films and the catalytic performance of OER.Firstly,the changes of crystal structure before and after laser irradiation on CoFe₂O₄ thin films grown on FTO glass were compared.It was found that laser irradiation did not cause significant changes in the overall structure of the material.However,as the laser irradiation time increases,the surface morphology of the sample gradually becomes denser and denser from the initial island-like stacking.Moreover,the laser irradiation has a great influence on the electronic structure of the surface,and the chemisorption caused by oxygen defects was significantly enhanced.The OER catalytic performance of CoFe₂O₄ thin films is obviously controlled by the combined effect of surface morphology and surface oxygen vacancy content.The role of the reaction potential of OER exhibits a volcano shape as a function of the irradiation time.That is,as the laser irradiation time increases,the reaction potential decreases first and then rises.The fourth chapter summarizes the main results obtained in this paper,explains the feasibility of the laser irradiation method to regulate the oxygen defect content on the surface of the catalyst.And this method provides strong support for the research of oxygen defect for the regulation of catalysts activity.