The Effect Of Metal Oxides On(Photo)Electrocatalytic Water Production Of Oxygen And Hydrogen Peroxide

The water decomposition reaction is an environmentally friendly,easy to operate and safe mathod to produce clean energy.Water decomposition can produce high energy density chemical energy and high value-added chemicals such as H₂ and H₂O₂.Therefore,it has attracted much attention from scientific researcher and industry.Among them,the water oxidation reaction,which is one of the half-reactions of water splitting,mainly includes a 4-electron process and a 2-electron process.Oxygen production by water oxidation is based on a 4-electron reaction process.Under the action of a catalyst,water is dehydrogenated and converted into O₂,and at the same time the cathode obtains clean energy of H₂.However,its reaction kinetics is slow,and becomes the rate-determining step of the water splitting reaction.Therefore,in order to improve the overall efficiency of oxygen production in the 4-electron process of the water oxidation reaction,it is very important to develop catalysts with high conversion efficiency,high stability,low cost and environmentally friendly.For the 2-electron process of water oxidation reaction,the water on the anode is oxidized to H₂O₂,while on the cathode reduced to produce H₂.Because this process can obtain H₂ as well as H₂O_2,the high value-added chemical,it attracts the wide interest of researchers to produces H₂O₂ by the electrocatalytic water oxidation reaction 2-electron process.However,the 4-electron process of the water oxidation reaction is a competitive reaction of the 2-electron process of the water oxidation reaction.At present,there are few catalysts for the production of H₂O₂ by water oxidation,at the same time,the H₂O₂yield and reaction selectivity are urgently needed to be further improved.Therefor the2-electron process of water oxidation reaction,the development and utilization of improved catalysts are very important for the application of this process.As an anode material for oxygen production by water oxidation,copper tungstate（CuWO₄）has received extensive attention due to its characteristics of simple preparation method and good light absorption.However,the poor charge separation and transfer properties result in low photoelectric catalytic performance of CuWO₄.So,it is of great significance to improve the charge separation and transfer properties of CuWO₄for improving the photoelectric catalytic water oxidation efficiency.In this paper,in order to improve the photoelectrochemical performance of CuWO₄,oxygen vacancies are introduced into CuWO₄,which effectively improve the photoelectrochemical performance of CuWO₄.In addition,through density functional theory calculations,the effect of bulk and surface oxygen vacancies of CuWO₄ on the charge separation and transfer properties and on the mechanism of surface water oxidation kinetics are deeply explored.For the 2-electron water oxidation process,in order to promote the 2-electron process of the water oxidation reaction,as well as improve the efficiency of the electrocatalytic water oxidation to produce H₂O₂ and the accumulation capacity of H₂O₂in the solution,it is particularly important to choose the right electrocatalyst.Sb₂O₃ was first applied on the 2-electron process electrocatalytic water oxidation reaction to produce H₂O₂ in this paper,and it was found excellent to generate and accumulate H₂O₂.This paper studies the optimal potential of Sb₂O₃ to produce H₂O₂,its efficiency of producing H₂O₂,and its ability to degrade organic pollutants.Overall,this paper includes the following aspects:1、The first chapter outlines the 4-electron process and the 2-electron process of the water oxidation reaction.The 4-electron process of photoelectrocatalytic water oxidation reaction can produce O₂ and H₂,and the 2-electron process of electrocatalytic water oxidation reaction can produce H₂O₂ and H₂,which are more valuable.In the chapter,the energy absorption and conversion mechanism of semiconductor photoelectric catalytsts in oxygen production based on the 4-electron process is discussed,and the application as well as the current problems of CuWO₄ as a photocatalyst are briefly described.In addition,the properties and performance improvement methods of CuWO₄ are briefly introduced.This chapter also briefly describes the different preparation methods of H₂O₂ and the current research status of the electrocatalytic water oxidation reaction 2-electron process.It is found that there are few catalysts that can be used for the electrocatalytic water oxidation 2-electron process to produce H₂O₂,and development of new electrocatalysts with high-efficiency is urgent to solve this problem.Therefore,this chapter mainly elaborates the basis and the main research content of this thesis.2、The second chapter studies the effect mechanism of oxygen vacancies on the CuWO₄ photoanode used in the photoelectrocatalytic water oxidation 4-electron process to produce oxygen.The properties of the samples are analyzed,including the morphology,structure,photoelectric catalytic performance and so on.Morphology characterization showed that CuWO₄ was successfully prepared,the electrochemical analysis showed that CuWO₄ with oxygen vacancies had better photoelectric catalytic performance than original CuWO₄.The mechanism of the influence of oxygen vacancies on the catalytic performance of CuWO₄ was further studied through both theory and experiment,and it was found that the water oxidation kinetics of CuWO₄was enhanced by oxygen vacancies.Theoretical calculation results show that the activation barrier of H₂O dehydrogenation on the surface of CuWO₄ with oxygen vacancies is much lower than that of CuWO₄.In addition to these advantages,it has also been found that the oxygen vacancies on the surface will also act as recombination centers on the surface of the photoanode,accelerating the recombination of surface charges.3、In the third chapter,the application potential of Sb₂O₃ as an electrocatalyst to catalyze the water oxidation reaction 2-electron process to generate H₂O₂ is studied.Sb₂O₃ was first time found to be with higher efficiency and better H₂O₂ accumulation effect than other metal oxide electrocatalysts.Drop casting method was used to synthesize antimony trioxide（Sb₂O₃）thin film,and the film was used as an electrocatalyst for the first time to produce H₂O₂ in the 2-electron process of water oxidation.Sb₂O₃ film shows good performance of producing H₂O₂ and has excellent catalytic stability and H₂O₂ accumulation ability.When it is used to treat pollutants,it successfully reduces the concentration of pollutants.This indicates that the Sb₂O₃ film can be used as an electrocatalyst for the electrocatalytic water oxidation 2-electron process to produce H₂O₂.