Design And Properties Study Of Transition Metal-Based Nanoelectrocatalysts Based On Surface-Interface Regulation

The ever-increasing detrimental effects of traditional fuels on energy and the environment have stimulated extensive efforts worldwide to develop clean energy conversion and storage systems,including nitrogen fixation technologies,metal-air batteries,and water splitting devices.The nitrogen reduction reaction（NRR）is at the heart of nitrogen fixation technologies,while the oxygen evolution reaction（OER）,oxygen reduction reaction（ORR）and hydrogen evolution reaction（HER）are of paramount importance to metal-air batteries and electrochemical water splitting systems.Seeking high-performance catalysts to lower the kinetic energy barriers of these electrochemical reactions is the key to realizing efficient and clean energy conversion and storage technologies.The essence of the electrocatalytic reaction is that the catalyst on the electrode surface promotes the electron transfer reaction of the reacting molecules under the action of the electric field.Therefore,the surface/interface properties of the electrocatalyst not only determine the kinetic activity of the catalyst for the corresponding electrochemical reaction,but also play an important role in the rapid conduction and exchange of gases,ions,and electrons.Generally speaking,it is very essential for electrocatalysts to have sufficient surface/interface reaction area that can provide sufficient contact between the active sites and the electrolyte（reactants）.Secondly,rational regulation/modification of the electron and atomic structure of the catalyst surface and interface can greatly reduce the energy barrier of the corresponding catalytic reaction and improve the catalytic reactivity.Finally,the high conductivity of the catalyst can accelerate the rapid conduction of electrons on the surface interface,thereby accelerating the catalytic reaction process and reducing the generation of electrochemical polarization.In this thesis,starting from the important role of surface/interface nanoengineering on electrocatalysts,a series of high-performance catalysts are designed and developed by optimizing the key factors through various surface interface regulation strategies（such as surface modification,heteroatomic doping,heterostructure construction,etc.）.Besides,the as-prepared catalysts exhibit excellent performances in applications such as electrocatalytic water splitting,electrochemical reduction to ammonia synthesis,and zinc-air batteries.The research in this thesis will have certain guiding significance for us to deeply understand the relationship between material structure,electronic behavior and electrocatalytic activity.The specific content of this thesis is mainly divided into the following sections:1.The development of highly stable and high-performance electrocatalysts is a great challenge in the field of electrochemical NRR.Au₂₅-Cys-M(M=Mo⁶⁺,Fe³⁺,Co²⁺,Ni²⁺)catalysts were synthesized by anchoring the catalytically active metal cations on Au₂₅nanoclusters by regulating the type of grafted cations via a surface bridging strategy.In particular,the Au₂₅-Cys-Mo catalyst exhibits excellent NRR performance with high Faradaic efficiency（26.5%）and NH₃ yield(34.5μg h^-1 mg^-1_cat).The systematic X-ray absorption spectroscopic characterization results demonstrate that Mo is tightly connected to Au nanoclusters through sulfur as an electronic bridging intermediate,which optimizes the electronic structure of Mo.Electron energy spectrum and DFT calculation results show that the formation of Au-S-Mo bonds on the catalyst surface optimizes the electronic structure of Mo,which not only acts as NRR active sites to improve the adsorption capacity of the material for nitrogen but also promotes the subsequent nitrogen hydrogenation process.2.It is difficult to precisely control the synthesis of single-atom catalysts with specific configurations.A facile biomimetic enzyme-induced synthesis method was proposed to control the atomic configuration of the catalyst surface,and the pyrrole-type Mn-N₄ sites（PT-Mn N₄）were successfully synthesized on ultrathin carbon nanosheets.The existence of isolated pyrrole-type Mn N₄ single-atom sites was confirmed by systematic X-ray absorption spectroscopy and HRTEM characterization techniques.Theoretical simulation calculations and practical test results prove that the single-atom pyrrole-type Mn N₄ sites can facilitate the adsorption of oxygen molecules and the subsequent reduction steps,resulting in high ORR intrinsic catalytic activity over the full p H range.Meanwhile,the Zn-air battery assembled using PT-Mn N₄ catalyst as cathode exhibited a large peak power density and stable discharge curve.3.It is crucial to develop low-cost,easy-to-prepare catalysts with good HER and OER performance for efficient overall water splitting.Herein,a variety of methods such as bimetallic doping and heterointerface construction were used to successfully tune the surface electronic structure,and a class of hydroxide-derived catalysts based on Ni Fe Mn was constructed.The Fe,Mn element doping can not only tune the morphology（such as size and thickness）but also optimize the surface electronic structure,thereby improving the electrochemically active surface area and the intrinsic activity of the active site.DFT theoretical simulation results show that the construction of the heterointerface effectively optimizes the adsorption energy of H on the surface of the material,and improves the binding activity of H₂O,thus ensuring the effective adsorption of reactants.The as-prepared Fe and Mn co-doped Ni₃S₂ nanosheet catalysts（FM-NS）and Ni Fe Mn-LTH/FM-NS heterogeneous nanosheet catalysts（Ni Fe Mn-LTH/FM-NS）show the good OER performance(η₁₀=188 m V)and HER activity(η₁₀=110 m V),respectively.When the as-obtained catalysts are coupled in the electrolytic cell for water splitting,only a small voltage of 1.48 V can achieve the current density of 10 m A cm^-2.4.The multifunctional catalyst can simplify the structure and cost of the energy conversion devices,but how to construct catalyst systems containing multiple active species for different half-reactions is still a topic worthy of exploration.A MOF-induced strategy approach was developed to construct heterostructures to tune hierarchical porous heterointerfaces.This hierarchical trifunctional electrocatalyst was composed of Co/Co S nanoparticles（NPs）and metal（Co,Fe）-N-C species embedded in a hairy S,N-codoped porous carbon polyhedral interwoven with CNTs（Co/Co S/Fe-HSNC）.A series of controlled studies showed that the introduction of Cd S into ZIF-67 as a pore former and sulfur dopant promoted the formation of Co S and S,N doped carbon.Meanwhile,ferrocene was used as an initiator for CNTs and Fe-NC species,which effectively enhances the catalytic activity and mass transport.Benefiting from these advantages,the Co/Co S/Fe-HSNC heterostructure catalyst exhibits excellent ORR,OER,and HER activities and durability in alkaline media.The assembled rechargeable zinc-air battery with the Co/Co S/Fe-HSNC catalyst as the air cathode exhibits a high power density of 213m W cm^-2,which are superior to Pt/C catalyst.5.The rational integration of various functional active sites in binder-free electrodes to synergistically enhance the multifunctional catalytic activity is crucial for enhancing the overall water splitting and Zn-air battery.A structural engineering strategy was proposed to develop a self-supporting trifunctional Co S₂/Fe S@SNC electrocatalyst based on carbon cloth by controlling the surface composition of the porous heterostructure-integrated electrode.The Co S₂/Fe S nanoparticles are anchored on S,N co-doped carbon triangular plate arrays.This unique 2D-on-3D structure realizes the synergistic effect between Co S₂/Fe S and S,N co-doped carbon,which not only facilitates ion and electron transport but also provides abundant accessible active sites.Therefore,the integrated Co S₂/Fe S@SNC electrocatalyst exhibits excellent catalytic activities for ORR,OER and HER.In addition,both liquid and flexible solid-state rechargeable zinc-air batteries assembled with this catalyst as air electrodes exhibit extremely high peak power density and ultra-long charge-discharge cycle durability.