Defect Engineering Regulates The Electrocatalysts For Electrocatalytic Performance

With the rapid development of modern society,the over-reliance on traditional fossil energy has caused serious energy and environmental problems.Therefore,developing new energy sources,which are clean,efficient,and sustainable,has become one of the most important challenges to build a global sustainable energy system for the future.New energy storage and conversion processes based on the reaction of hydrogen(H₂)and oxygen(O₂),such as electrocatalytic water splitting,metal-air batteries etc.,have received more and more attention.Among these devices,the electrocatalysts required for the elementary reaction process play an extremely critical role on the whole performance.The ideal electrocatalyst can effectively improve the performance of the device.Therefore,how to rationally design and develop new catalysts with high efficiency and low cost has become the top priority of building a new sustainable energy system.With the rapid development of various catalyst synthesis technologies and high-end characterization methods,researchers can understand the dynamic process of the reactions and understand the in-situ activation mechanism of the catalyst deeply.The conclusions can guide other researchers to prepare ideal electrocatalysts with more excellent performance and lower cost.Recently,scientists have developed various surface engineering methods to regulate the electronic structure of the catalysts and then enhance their catalytic activity.Among various surface engineering methods,defect engineering strategies have attracted much attention.Defect engineering can precisely control the surface composition of the materials on the atomic scale,changing local microenvironment,adjusting the electronic structure and promoting catalytic performance.This thesis mainly uses defect engineering strategies to control carbon-based and transition metal-based catalysts,introducing different types of defects into the catalyst,and adjusting the electronic structure of the catalyst,optimizing the adsorption and desorption of the reaction intermediates,thereby enhancing the catalytic reaction activity.On one hand,by introducing defect sites in the catalyst to regulate its inherent proprities and promote the catalytic performance;on the other hand,using the high activity proprities of defect sites,we can introduce new elements with specific functions at the defect sites to control the catalyst and make it have a multi-functional catalytic functions.The detailed researches are described below:(1)The heteroatom-doped defects can effectively regulate the electronic structure of the catalyst and affect its catalytic activity.In this chapter,we use the method of electrochemical polymerization and molecular assembly to prepare the N and P co-doped carbon materials.The results show that the nonmetallic N,P co-doped porous carbon catalyst prepared by this strategy shows excellent HER activity and stability.Comprehensive physical characterization proves that P atom was successfully introduced into N-doped carbon materials.The synergy effect of N and P atoms can generate more defect sites.The increasing number of active sites effectively enhance the HER activity.This work opens up a new electropolymerization method to prepare uniform porous carbon materials with doped heteroatoms,which was grown directly on the substrate,providing new ideas for the design and preparation of efficient carbon-based HER catalysts.(2)To effectively screen the doping atoms can induce new functions to promote specific catalytic reactions.In the work of this chapter,in order to promote the dissociation step,which was the first step of HER in alkaline,the doping Ru single atoms into the Ni particles supported on carbon material was successfully achieved.Introducing the metal Ru with super strong water dissociation ability into the Ni metal with a relatively moderate hydrogen Gibbs free energy,Ru atomic level dispersion can greatly increase the sites of dissociation water,making each Ru atom work.In addition,the adsorbed H produced by Ru dissociation water can be rapidly catalyzed by the surrounding Ni atoms to further produce hydrogen.Synchrotron radiation XANES proves that Ru is doped in the form of a single atom into the elemental Ni.Electrochemical test results show that,compared with the pure carbon-supported metal Ni catalyst,the basic HER performance of Ru single atom doped electrocatalyst is significantly improved,and it only requires 55 mV overpotential to reach a current density of 10 mA cm^-2.The work in this chapter introduces the design of two-component catalytic sites through doping can successfully achieve efficient hydrogen production under alkaline conditions.(3)Transition metal-based catalysts can be regulated by changing their coordination environment and introducing coordinated unsaturated centers to improve their activity.This chapter further studies the effect of the coordination unsaturated metal centers on the performance by directly destroying the coordination bond of the catalyst.A series of physicochemical characterization confirmed that using DBD plasma to destroy part of the Co-O bond in Phy-Co²⁺can generate much metal coordination unsaturated sites.Electrochemical test results show that the P-Phy-Co²⁺sample exhibits very excellent OER performance,which requires only 306 mV overpotential to obtain a current density of 10 mA cm^-2,while the original sample Phy-Co²⁺requires 383 mV.Further analyzing its Tafel slope and it can be inferred that the generation of the metal coordination unsaturated centers can optimize the adsorption energy of the OER reaction intermediate species(*OH,*O,*OOH),thereby significantly improve its OER performance.This work directly studies the effect of the coordination unsaturated centers of catalysts,highlighting the important role of coordinated unsaturated defect sites.(4)The defect site is more active,and this feature can be used to induce new functional atoms or molecules to the defect site and make it have new functions.In this chapter,Co₃O₄,which normally has OER activity but relatively inert HER activity,is used as the study object.The CH₄treatment at room temperature is used to construct rich oxygen vacancies and realize in-situ modification of C heteroatoms,making it as both HER and OER bifunctional catalysis.Electrochemical test results show that the inducing of C heteroatoms makes the Co₃O₄catalyst exhibit excellent alkaline HER activity,which requires only a 163 mV overpotential to obtain a current density of 10mA cm^-2.DFT calculation results show that the inducing of C heteroatoms can not only improve its conductivity,but also adjust its adsorption free energy for intermediate species,making H(?GH*)in HER is closer to 0,optimizing OER intermediate species O*and OOH*.In this work,the introduction of new functional atom at the defect site to form a new catalytic microenvironment has further enriched the study of defects.