Construction Of Oxides-Supported Catalysts Based On Surface/Interface Modulation And Their Performances In Water Electrolysis

As a renewable,clean and efficient secondary energy source,hydrogen energy（H₂）plays a significant role in the global-energy-structure transformation.Among various commercial hydrogen production processes,water electrolysis driven by renewable electricity has became a vital way to obtain green hydrogen because of its high purity of H₂ product,minimal CO₂ footprint and convenient operation.Water splitting is divided into two half-reactions,namely cathodic hydrogen evolution reaction（HER）and anodic oxygen evolution reaction（OER）.However,its sluggish reaction kinetics leads to high energy consumption.Therefore,the development of efficient,low-cost and stable electrocatalysts is one of the key technologies for future hydrogen energy systems.In order to achieve the dual optimization of performance and cost of electrocatalysts,the rational development of supported metal-based electrocatalyst is one of the most promising ways to realize this goal.However,the optimization of the interfacial microstructure and the exploration of the intrinsic structure-activity relationship have been one of the core and challenging topics in the field of heterogeneous catalysis for a long time.Based on the basic principal of electrocatalysis,this thesis concentrates on developing various surface/interface structure modulation strategies（morphology/component modulation,support engineering modulation,strain effect modulation,and heteroatom doping modulation）to enhance the activity and stability of oxides-supported electrocatalysts.Combining advanced physicochemical characterization,electrochemical analysis,in-situ spectroscopic characterization and theoretical calculations,the microstructures and intrinsic activity-structure relationships of the electrocatalysts were comprehensively analyzed from multiple perspectives,which provides theoretical guidance for the development of new generation of oxides-supported electrocatalysts for water splitting systems.（1）In second chapter,using a morphology/component modulation strategy,Ni Mo carbide/oxide/carbon cloth flexible electrocatalyst with three-dimensional hierarchical structure is successfully constructed by annealing Ni Mo O₄ nanoarrays grown on activated carbon cloth（ACC）in a H₂ atmosphere.The rate of carburization reaction is regulated by changing the temperature and time of annealing treatment to further optimize the components,morphology and surface properties of the catalysts.The uniformly dispersed Ni Mo carbide nanodots（～3.5 nm）provide a large number of active sites to enhance the dissociation of water molecules and optimize the adsorption strength of H_ad(ΔG_H*=-0.13 e V,ΔG_H*on Pt is-0.18 e V).The oxygen-defects Ni Mo O_xnanosheet array structure not only enhances the catalyst conductivity and bubble mass transfer process,but also effectively prevents the agglomeration of Ni Mo carbide nanodots.The unique flexible mechanical properties and the strong interfacial adhesion of the ACC substrate ensure that the active components can operate stably under complex operating conditions.Thanks to the unique muti-hierarchical structure and the synergistic effects of the components,the optimized Ni₆Mo₆C/Ni Mo O_x/ACC exhibits comparable or better activity and stability than commercial Pt/C（20 wt%）catalysts in alkaline electrolytes.These findings afford a new idea to integrally construct highly efficient and flexible self-standing electrocatalysts.（2）In third chapter,the Ir-H_xWO₃ composite catalyst is constructed by using the support engineering strategy,where WO₃with excellent proton storage capacity and conductivity is selected as a support followed by electrochemical deposition of Ir metal nanoparticles（～1.7 nm）.The combination of electrochemical analyses,electrochromic reaction and spectroscopic results reveal that the WO₃ support spontaneously undergoes proton-electron co-insertion to generate H_xWO₃ in the HER potential region.On the one hand,the semiconductor-conductor conversion accelerates the interfacial charge transfer and enhances the conductivity of the material;on the other hand,H_xWO₃ acts as a proton sponge to form an acidic microenvironment around metalic Ir sites,which successfully overcomes the problem of sluggish kinetics caused by the lack of proton concentration in neutral media.Thus,Ir-H_xWO₃ breaks the traditional p H-dependent kinetic limitations of HER and exhibits indistinguishable HER activity(neutral:η₁₀=20 m V,acidic:η₁₀=19 m V)and reaction kinetics（neutral:28 m V/dec;acidic:25m V/dec）in neutral and acidic media.In contrast,commercial Ir/C and Pt/C catalyst systems exhibit dramatic performance differences in acidic and neutral media.In-situ Raman spectroscopy tests,selective poisoning experiments,isotope effect experiments and theoretical calculations all clearly reveal that a fast neutral hydrogen production rate was achieved between the W-OH and Ir-H*through thermodynamically favorable Vomler-Tafel pathway.This work provides new opportunities for the deployment of mild energy storage and conversion systems and direct seawater electrolysis for hydrogen production.（3）In fourth chapter,a strategy of strong oxides-sopport interaction（SOSI）induced strain effect is adopted to successfully manufacture the Ir O₂/V₂O₅ system by annealing Ir/V metal-organic framework in air atmosphere.Ultrafine Ir O₂ nanoclusters（～1 nm）are anchored on 3D porous framework of V₂O₅support,thus greatly increasing the exposure of active sites.The SOSI effect between Ir O₂ and V₂O₅ is confirmed by advanced electron microscopy,comparative experiments and theoretical simulations,which optimizes the geometric/electronic structure of the Ir active sites,i.e.,the lattice distorted Ir O₂ nanoclusters expose more unsaturated coordination active sites and the charge transfer between Ir and V enhances the redox properties of the electrophilic Ir O₂sites.DFT calculations indicate that strain effect optimizes the d-band center of Ir and weakens the Ir-O*bonding strength,thus reducing the reaction energy barrier of*O to*OOH.Therefore,compared with commercial Ir O₂,the Ir O₂/V₂O₅ catalyst exhibits excellent OER activity(η₁₀=266 m V,p H=0;η₁₀=329 m V,p H=7;η₁₀=283 m V,p H=14)and catalytic stability（20 h at 10 m A/cm²）in all-p H media.More importantly,the Ir O₂/V₂O₅ can be used as bifunctional electrocatalysts to drive water splitting at only 1.50 V（p H=0）,1.65 V（p H=7）,or 1.49 V（p H=14）at 10 m A/cm².This catalytic system is expected to be used in a variety of scenarios for energy conversion processes due to its high degree of compatibility.（4）In fifth chapter,using the heteroatom doping modulation strategy,the rare-earth-metal Tm is doped into theα-Mn O₂/Ti nanorod support by a simple hydrothermal method,and then the Ir O_x/Tm-Mn O₂/Ti electrocatalyst is successfully prepared by impregnating the Ir precursor and subsequent heat treatment in air atmosphere.Combining with H₂ temperature-programmed reduction（H₂-TPR）,electron paramagnetic resonance（EPR）and X-ray photoelectron spectroscopy（XPS）,it is confirmed that the doping of Tm introduces a large number of oxygen defects（O_v）and Mn³⁺species.Oxygen defects act as anchor sites to disperse the Ir O_x nanoclusters（～0.8 nm）,thus significantly enhancing the catalytic activity and stability.In acidic OER test,Ir O_x/Tm-Mn O₂/Ti requires only 211 and 402 m V overpotentials to achieve current densities of 10 and 500 m A/cm²,respectively.Compared with Ir O_x/Mn O₂/Ti and Ir O_x/Ni-Mn O₂/Ti systems,the stronger d-f orbital interaction between Tm-Mn greatly alleviates the loss of Mn at high anode potential to avoid the collapse of the structure.The Ir O_x/Tm-Mn O₂/Ti electrocatalyst can operate stably for 500 and 100 h at current densities of 10 and 500 m A/cm²,respectively.