Preparation Of Transition Metal-based Organic Framework Materials And Their Electrocatalytic Performance For Oxygen Evolution

Energy is the main driving force for the development of human society.The development of clean and efficient new energy and renewable energy to replace traditional fossil energy is of great significance to the sustainable development of my country’s economy.Electrocatalytic water splitting is one of the ideal methods for developing clean energy,but the high cost also limits the process of industrialization.Therefore,it is very important for the development of industry to develop cheap and excellent catalysts to reduce the reaction energy barrier.Metal organic framework（MOF）materials are particularly useful in the field of catalysis due to their large specific surface area,high porosity,adjustable structure and monodisperse active centers.At present,although the MOF prepared by traditional methods contains catalytically active metals,the metal sites in the MOF are usually combined with organic ligands and cannot be well exposed,resulting in very low activity in the catalytic process.Not only that,but its poor electrical conductivity and structural stability are also difficulties in the application of MOF in the direction of electrocatalysis.For this reason,we select foamed nickel as the matrix,grow transition metal-based MOF material in situ,adjust the microstructure and composition of MOF,effectively improve its electronic conductivity and the exposure of active sites,and prepare a highly active and stable product.The double transition metal organic framework catalyst.The specific work content is as follows:（1）A series of NiFeMOF/NF with two-dimensional layered structure was synthesized by a simple one-step water bath method.By controlling the reaction time,the growth behavior of the two-dimensional layered structure on the nickel foam was explored.Due to the surface tension between the surface atoms and the dissolution-crystallization mechanism,the MOF material grown in situ can form a two-dimensional layered upright grid structure that is uniformly covered on the NF.The upright two-dimensional structure provides more exposed active sites for the material due to its edge effect,which can effectively improve its catalytic activity.（2）By controlling the addition of Ni and Fe in NiFeMOF/NF to synthesize MOF materials with different NiFeratios.After introducing Fe into Ni MOF/NF,with the increase of Fe content,the conductivity and OER performance of NiFeMOF/NF are significantly improved.This is due to the metal synergy between Ni and Fe.However,when Fe is added in a larger amount than Ni,a decrease in electrocatalytic OER performance is observed because the formation of Fe OOH impairs OER performance.The OER activity of NiFeMOF/NF is the best when the NiFeratio is 8:2.Under alkaline conditions,only an overpotential of 260 m V is required at a current density of 50m A·cm^-2.（3）In order to solve the instability of MOF in the growth process,we use solutions of different polarities to control the diffusion of metal ions,so as to synthesize NiFeMOF on foam nickel stably and uniformly.The dissolution of organic ligands by organic solvents（such as methanol,ethanol,acetone,N,N-dimethylformamide）and their polarity will affect the morphology and structure of MOF synthesized on foam nickel in situ.The smaller the polarity of the solution,the slower the diffusion of metal ions,which is more conducive to the full dissolution of the organic ligand dipotassium 2,6-naphthalate and the combination with metal ions.The NiFeMOF/NF electrode prepared in the lowest polarity acetone solution has excellent OER performance.It provides high current density at an overpotential as low as 270 m V,the Tafel slope is 55 m V·dec^-1,and maintains excellent stability.（4）To further optimize the stacking problem of the two-dimensional structure during the growth process.We synthesize nanowire-shaped Co（OH）₂ NWs by hydrothermal method,and use this as a template to synthesize Co-Fe MOF/NF similar to dragon fruit leaves.This method of synthesizing a two-dimensional structure using a one-dimensional structure not only preserves the good structure of the nanowires,but also effectively avoids the occurrence of two-dimensional layered agglomeration and stacking.Control the microstructure of the material to further form a new two-dimensional structure to expose as many active sites as possible or effectively increase the intrinsic activity of each site.In addition,the addition of Fe enhances the synergy between metals,thereby effectively improving the electrocatalytic performance of the catalyst.When the Fe content is 5 mg,Co-5Fe MOF/NF can reach a current density of 50 m A·cm^-2at 284 m V,and the Tafel slope is only 66 m V·dec^-1.