Synthesis Of Hierarchical Porous Nano Metal-Organic Framework MTP-ZIF-67 And Its Application In Electrochemical Capacitors

For electrode materials,the porous structure can improve the performance of the material.For example,it can significantly increase the specific surface area of the material and promote the transport of electrolyte ions and reduce the contact resistance,which will improve the storage performance of the device.Metal-Organic Framworks（MOFs）have been widely studied and applied in the field of supercapacitors due to their porous structure.However,the interior of traditional MOFs has a microporous structure,which is not conducive to the rapid transport of ions,and that limits the application of MOFs in the field of electrochemistry.At present,macroporous materials can be effectively prepared by methods such as templating and extending ligands,but there are also some problems such as limited pore size and low structural stability.Therefore,fabricating MOFs with highly stable macroporous structures plays an important role in improving material properties and facilitating practical applications.For the current situation,this paper proposes a new type of supramolecular hydrogel template:N,N’,N’’-tris（3-pyridyl）trimesic amide organic nanofibers.The macroporous cobalt-based zeolite imidazolate framework with through-tubular pore structure（MTP-ZIF-67）was obtained by soaking the Co²⁺/TPTA supramolecular hydrogel with 2-methylimidazole and then removing the gel fibers.In this process,macropores are obtained by the insertion and removal of organic nanofibers.The MTP-ZIF-67 has excellent electrochemical performance and can achieve controllable adjustment of the structure.It is also found that this macroporous structure does not reduce the electrochemical cycle stability of the material while improving the performance.The specific research work contents are as follows:（1）Firstly,we adopted a supramolecular hydrogel-based template,using TPTA as a matrix,mixed with cobalt acetate to obtain a homogeneous composite hydrogel,and after the process of particle growth and template removal,a macroporous cobalt-based zeolite imidazolate framework（MTP-ZIF-67）with a through-tubular structure was obtained.The particle size of MTP-ZIF-67 is 1.5-3μm,and the pore size is 2-170 nm.The pore channel is a through structure in the interior of the particle,and the pores are connected with each other.Through the characterization of the xerogel fibers,it is proved that the appearance of through-tubular pore is caused by the embedding and removal of the gel fibers in the particles.（2）Using the above MTP-ZIF-67 as electrode material and PVA-H₂SO₄ as gel electrolyte to fabricate symmetric flexible all-solid-state supercapacitors.When the current density is 10 m A cm^-2,the specific capacitance reaches 2116 m Fcm^-2,which is 25%higher than that of the microporous material.After 5000 times of charge and discharge,it can maintain more than 70%of the initial performance.In the liquid electrolyte,the capacitance performance of MTP-ZIF-6/CC/PANI can reach 3415 m F cm^-2 under the current density of 10 m A cm^-2,and the synergistic effect of PANI is important for the improvement of electrochemical performance.（3）By adjusting the amount of hydrochloric acid in the gel to reduce the diameter of the gel fibers,the particles with a pore size of about 20 nm are obtained,and this pore size is half of that in the standard experiment.By adding organic solvent ethanol to the gel,the particles with a pore size of80-150 nm are obtained,and the organic solvent will significantly reduce the particle size of MTP-ZIF-67.In the pore density adjustment experiment,increasing the amount of TPTA to twice that of the standard experiment can increase the pore density on MTP-ZIF-67,while the uniformity of pore distribution on particle surface can also be increased;reducing the amount of TPTA to 1/2 of the standard experiment results in a significant decrease in the pore density on the particles.The template can realize the controllable adjustment of particle size,pore size and pore density in three directions.In addition,using zinc acetate replace cobalt acetate,2-methylimidazole ligand was added to soak for 24 h,and then the template was removed to obtain a hierarchical porous zinc-based zeolite imidazolate framework（ZIF-8）with through-tubular structure.The particle pore size is about 50 nm,and the pores are uniformly distributed on the particle surface,so that the TPTA gel system not only limited to the preparation of ZIF-67 MOF.