Modulating The Performance Of Electrocatalytic Water Oxidation By Concomitant Polymorphs Of Mononuclear Nickel Complexes And Heterometal Cooperation Effects Of 3d(Ni,Ru)-4f(Ce,Eu) Compounds

Aiming at responding to the goal of"Dual Carbon"and promoting sustainable energy development,the production of oxygen/hydrogen by photolysis/electrolysis water is considered as one of the effective strategies for alleviating energy consumption.Considering the major bottleneck of artificial Photosystem II:the slow kinetic process of four-electron-four-proton,it is necessary to develop efficient and robust water oxidation catalysts（WOCs）.Based on the characteristics and limitations of materials,metal oxides with catalytic activity,mononuclear or polynuclear transition metal complexes and 3d-4f coordination clusters have been developed successively.Beneficial from the ease of exploring the catalytic mechanism by a variety of characterization methods,efficient and stable metal complexes with clear structures have become a research hotspot.In order to improve the stability and catalytic activity of molecular catalysts and explore the relationship between catalytic mechanism and structure,this paper intends to study through the following four parts.Chapter 1 mainly introduces the research background and development process of electrocatalytic water oxidation catalyst,summarizes the research status at home and abroad,puts forward the prospect of its development and application,and expounds the basis of topic selection and research innovation,including research content and implementation method.Chapter 2 simulates the different OER properties of a variety of phase changes metal oxides,mononuclear 3d metal complexes with different crystal stacks were loaded on the electrode,the OER performance can be regulated by changing the external conditions and adjusting its configuration transformation.Due to different stacking forms,mononuclear nickel complex Ni L₂（L=2-ethoxy-6-（N-methyliminomethyl）-phenolate）exhibites two crystal packing disparities,i.e.,green monoclinic P₂₁/c symmetry（Ni L₂-G）and red orthorhombic I_bam symmetry（Ni L₂-R）.The overpotential of Ni L₂-R（339 m V）is lower than that of Ni L₂-G（466 m V）under 10m A/cm².The DFT calculation shows the intermediate R-L₂Ni^Ⅲ-OH is more stable than G-L₂Ni^Ⅲ-OH,and forming L₂Ni^IV=O from the former R-L₂Ni^Ⅲ-OH has a much lower barrier than that from the latter.It explains that controlling the external conditions and adjusting the crystal packing mode of 3d metal complexes is one of the effective ways to regulate the catalytic performance of electrolytic water.In Chapter 3,molecular design and in-situ doping are used to realize the synergistic coupling of different metals to regulate the catalytic performance of 3d-4f complexes.According to the OER activity volcanic diagram of metal oxides,heterometal doping can significantly improve the activity of catalysts.The introduction of 4f metal can stabilize the frame structure under a high oxidation state.Therefore,based on the above advantages,it is proposed to realize the synergistic coupling of different metals to regulate the catalytic performance of 3d-4f complexes through molecular design and in-situ doping.Firstly,polydentate Schiff base ligands with both soft and hard coordination sites were designed and synthesized,and chelated 3d and 4f metal ions with the N₂O₂O₂ coordination cavity respectively to obtain a 3d-4f metal complex with a well-defined structure.It is found that when the optimal molar ratio of Ni/Fe is 1:1,its stability is greatly improved,and its overpotential is 290 m V under 20 m A/cm².To further enhance the catalytic activity of 3d-4f complexes,besides Ni/Fe of 1:1 molar ratio of doping at the same time,we further doped Eu with Ce,the overpotential further decreases to 264 m V under 20 m A/cm²,achieving the best catalytic performance among molecular catalyst electrolysis of water that has been reported so far.The mechanism study shows that 3d metal doping improves the binding of OH^-and the dissociation of electrons.Although 4f metal can not be directly involved in the formation of O-O bond,it can receive the electrons transferred comes from 3d metal,and jointly improves the catalytic performance and catalytic stability of the catalyst.In Chapter 4,the effect of Ce on catalytic performance was studied by introducing Ce with different valence into homogeneous catalytic system.Most of the previously reported ruthenium pyridine carboxylic acids show high photocatalytic water oxidation performance with Ce⁴⁺used as oxidant.Since Ce⁴⁺can easily form 3d-4f coordination clusters with carboxylic acids through chelation bridging mode,synergistic catalysis is realized through 3d-O-4f.However,there is a lack of study and Discussion on the catalytic performance and mechanism in the literature when Ce⁴⁺exist.It was found that the peak overpotential of homogeneous electrocatalyst Ru（pic）₂L（pic=4-Methylpyridine）in 1 M neutral phosphate buffer（PBS）is 317 m V and TOF=9.6 s^-1.In the presence of Ce³⁺or Ce⁴⁺,the peak current intensity of water oxidation of the former is almost unchanged,while that of the latter increased from 2.3 m A/cm² to 4.3m A/cm²,which confirmed that Ce⁴⁺can also promote the electrocatalytic performance of Ru-based catalyst.