Research On Ferrous Metal Organic Frame Materials For Supercapacitor Field

With the development of distributed power generation technology,the requirements of microgrides for energy storage technology are increasing.Compared with various energy storage technologies,the super capacitor energy storage system responds quickly and sensitively,and has the advantages of high output power and high efficiency,which has become the focus of research in energy storage systems.Generally speaking,the performance of supercapacitors mainly depends on the quality of electrode materials,so the research and development of highly active electrode materials has become one of the hot spots in the field of supercapacitors.With the joint efforts of scientific researchers,a large variety of new supercapacitor electrode materials have been developed successively,such as carbon materials,metal oxides,composite materials,conductive polymers,and so on.Among them,metal organic framework（MOF）materials,as a new type of porous crystalline materials,have the advantages of high porosity,large surface area,adjustable composition,design tailoring and easy access to active sites,making them bacome one of the potential materials for constructing an ideal supercapacitor electrode material.Unfortunately,most of the MOF materials’ electrical conductivtiy,chemical stability are still relatively poor.Therefore,the application of MOF-based electrode materials in supercapacitors still has huge challenges.Regarding the issue above,This article selects classic iron-based MOF materials as the basis for research,and uses different methods to modify its conductivity,stability,and reactivity in order to improve its supercapacitor performance and explore its mechanism,which provides a feasible research scheme for the wide application of MOFs-based materials in capacitors.The details are as follows:The number of metal active sites and their reactivity are two important factors that affect the performance of capacitors.Base on this,we used terephthalic acid as the organic element to construct a two-dimensional（2D）ultra-thin iron-based bimetal NiCo-MOF nanomaterial using a one-step hydrothermal method.Based on the basic physical characterization,the supercapacitor performance test was found.The performance of the2 D NiCo-MOF nanosheets was significantly better than that of iron-based single-metal Ni-MOF/Co-MOF electrode materials.XPS and XANES analysis resulted that the electrons around Ni2+ in NiCo-MOF electrode material were transferred to Co²⁺ made the former metal ion have a higher oxidation state;the higher valence Ni cation has a stronger ability to accept electrons,which can accelerate the charge transfer between the electrodematerial and the electrolyte,thereby improving the chemical reaction activity.In addition,the ultra-thin thickness of the nanosheets can provide a large amount of electrochemical surface area and more metal active sites,which is greatly beneficial to the redox reaction.The result is that NiCo-MOF nanosheets exhibit excellent supercapacitor performance,with a specific capacitance of 1945.83 F g-1at a current density of 0.5 A g-1.In addition,the successful preparation of bimetal Ni Mn-MOF nanosheets and the study of its electrochemical properties further confirm the above mechanism.This work provides a new idea for the design of MOF-based materials with excellent capacitance performance.In order to improve the conductivity of MOF materials,the author used a small amount of MXene nanosheet components with metal conductivity and rich hydrophilic surface groups in the system.Taking Co-BDC as an example（using terephthalic acid as an organic ligand,Co Cl2 · 6H2 O provides metal ions and constructed by a one-step hydrothermal method）,a Co-BDC/Ti3C2 Tx hybrid nanosheet with tight coupling effect was constructed by adding a cobalt salt and an organic ligand to Ti3C2 Tx nanosheet dispersion,and adopting a simple one-step hydrothermal method.After heat treatment at 300℃ for 1h in an Ar atmosphere,the force between the hybrid nanosheet components was strengthened.XPS characterization concluded that heat treatment enhanced the coupling effect between Co-BDC and Ti3C2 Tx,and the electrons transfered from the Ti3C2 Tx nanosheets through the Ti-O-Co interface increased the Co-BDC’s Conductivity.On the other hand,after electrons transferred,the valence of Ti ions in Ti3C2 Tx were increased,which can also increase its own redox activity.As a result,the Co-BDC/Ti3C2 Tx hybrid nanosheets exhibited excellent capacitance performance.When the current density is 0.1 A m-2,the specific capacitance reaches 2265.36 F m-2.In addition,the design and synthesis of Ni-BDC/Ti3C2 Tx system further supports the above strategy,opening a new way for the research of electrode materials for MOF-based strongly coupled hybrid nanosheet supercapacitors.Adding a conductive material with a pseudocapacitive property to the electric double layer material can greatly improve the capacitor performance.We constructed Co-BDC/Ti3C2 Tx hybrid nanosheets by a simple one-step solvent reaction,and then annealed them at 550 ℃ in Ar atmosphere to obtain Ti₃C₂T_x/Co-C nanomaterials.Through a series of electrochemical performance tests,it was found that proper incorporation of Ti3C2 Tx can effectively enhance its supercapacitor performance.The specific capacitance reached 1010.45 F m-2 at a current density of 0.5 A m-2,which is 5.1times the capacitance performance of pure Co-C material（197.29 F m-2）.The reason was that the increase of Ti content promoted charge transfer on the Ti-O-C/Co surface.