Preparation Of Bifunctional Cobalt/Iron-Based Metal-Organic Frameworks Electrode Based On Functional Group Regulation And Its Performance In Water Splitting

Metal-organic frameworks（MOFs）,as highly crystalline porous materials,have become a new type of electrocatalysts with broad application prospects due to their physical properties such as high specific surface area,metal selectivity and organic ligand diversity.At present,although a variety of MOFs based materials have been reported,the industrial application of pure MOFs is still limited due to its poor performance in the field of catalytic hydrogen production.Modification of MOFs,such as the introduction of functional groups to regulate the local electronic states of MOFs,is an effective strategy to improve the catalytic performance.This paper aims to design bifunctional electrodes with high catalytic activity based on functional group regulation of MOFs,and the physical and chemical changes of MOFs materials in the process of hydrogen evolution（HER）,oxygen evolution（OER）and overall water splitting are taken as the research object.The research mainly includes the following two parts:（1）Preparation and Properties of MOFs Bifunctional Electrodes Modified with-NH₂ and-COOH Functional GroupsFirstly,MOFs were synthesized by two steps of hydrothermal synthesis in situ on the nickel foam（Ni）skeleton,and the MOFs with rich functional groups were formed after the introduction of organic ligands.The structural characteristics and material properties of MOFs were proved by XRD,XPS,FT-IR,etc.By changing the ligand,metal center and functional group,the precursor unit can be regulated.By electrochemical test,the optimal MOFs（σ-Fe/Co-N-ligand/NF）can achieve the current density of 10 m A cm^-2 and maintain the stability for at least 100 h when the overpotential is 1.468 V.The optimized atomic conversion rate（TOF）is 0.056 s-1,which is much higher than the reported MOF-based catalyst.In the catalytic process,the Co-N and Fe-N bonding units formed between Co/Fe and-NH₂ functional groups act as the center of HER,and the-NH₂ and-COOH functional groups activateπelectrons intoπ*electrons,which contributes to the interaction between molecules.（2）A universal strategy for modulating carbon-supported transition metal oxide by electron-giving and electron-absorbing functional groups towards efficient overall water splittingFollowing the previous study,different types of electron-giving（-NH₂,-OCH₃ and-OH）and electron-absorbing（-COOH and-NO₂）functional groups were introduced to form cobalt-iron based MOFs to study the performance of HER,OER and overall water splitting.Research shows that:（1）for the MOF based electrocatalysts,introduction to electron-giving and electron-absorbing functional groups can improve the surface hydrophilicity and enhancing the interaction of catalytic electrolyte,so that the electrolyte has higher exposed the charge transfer and better than the site,improve the ability to attract each other between each constituent,which has good catalytic stability.（2）For MOF-based electrocatalysts,the introduction of electron-giving and electron-absorbing functional groups further affects the anchoring of metal ions.The metal cation Co with electron-giving functional group is helpful for anchoring,and the metal cation Fe with electron-absorbing group is helpful for anchoring.（3）For MOF-based electrocatalysts,the introduction of electron-giving functional group（-NH₂）and electron-absorbing functional group（-COOH）has a certain effect on carbon materials.-NH₂ functional group is the main cause of structural disorder of carbon materials.The-COOH group contributes to the further enhancement of the electronic structure of the ordered carbon,thus achieving excellent performance.The differences in the composition of carbon before and after HER and OER indicate that carbon atoms can activate theirπelectrons toπ*electrons through electron withdrawing functional group（-COOH）,which contributes to their excellent catalytic activity and stability.