Fabrication And Properties Of Hybrid OER Electrocatalysts Based On Bimetallic MOFs

In recent years,the development of high technology has led to the widespread application of new energy,which has promoted the development of economy and society.Among them,hydrogen energy has the most development potential because of its advantages of no carbon emission and high energy density.At present,hydrogen production by electrolysis of water is simple,and the purity of H₂ is high.The technology is relatively mature,and it is in line with the"carbon neutral"strategy,so it has a wide range of application prospects.Electrocatalytic water splitting consists of two half-reactions,hydrogen evolution reaction（HER）and oxygen evolution reaction（OER）.In particular,the kinetic process of OER,which involves O-H bond breaking,O=O double bond formation and four-electron transfer,is very slow,limiting the overall efficiency of electrolytic water.Therefore,there is an urgent need for efficient and stable catalysts to overcome the energy barrier and accelerate the OER reaction rate.Metal-organic frameworks（MOFs）have attracted much attention in electrocatalytic decomposition of water because of their unique periodic structure with abundant,tunable and uniformly distributed active centers.However,they are limited by their poor electrical conductivity and unstable catalytic activity at high current densities,which are far from meeting the requirements of industrial production.Herein,we design to optimize the metal active centers of MOFs by modifying heteroatoms.The obtained samples have hollow structures to regulate the material conductivity and compound conducting polymers to improve the conductivity and the stability of intrinsic MOFs.Thus,the electrocatalytic materials we fabricated have outstanding OER performance at high current densities.In chapter 2,a metastable bimetallic MIL-88（Fe Co）was first synthesized and then transformed into a bimetallic iron/cobalt-phytate complexes in situ growing conductive polymer polyaniline with hollow octahedron structures（FCP@PAn）.Moreover,we explored the effects of different aniline incorporation on the morphology and structure.The results showed that the required overpotentials of FCP@PAn-10 were 212,261,329 and 385 m V at current densities of 10,100,500 and 1000 m A cm^-2,respectively.And FCP@PAn-10 exhibited strong durability at 500 m A cm^-2 for 120 h.Component and structure modulation,N and P doping,and polyaniline compounding were carried out in one-step without the high temperature treatment of phosphorylation and carbonization.FCP@PAn-10 performed with excellent OER performance due to the synergy of multiple strategies.In chapter 3,MOFs modified with conducting polymer polythiophene were further investigated.FCP₁@PTh with an obvious hollow structure was prepared by adjusting the addition of phytic acid,hydrochloric acid and thiophene.Moreover,we explored the effects of different thiophene incorporation on the morphology,structure and OER electrocatalytic properties.The results showed that the required overpotentials of FCP₁@PTh-10 were 296 and385 m V at current densities of 100 and 500 m A cm^-2.FCP₁@PTh-10 exhibited strong durability at 100 m A cm^-2 for 150 h.The electronic structures of the metal active center were modulated by the introduction of S and P.The catalytic specific surface areas were increased and the paths of material transport were shortened by the more prominent hollow structure.In this work,composite electrocatalytic materials with hollow structures were prepared by the modification strategies of heteroatomic modification and polymer composite of bimetallic MOFs.Due to the synergistic effects of multiple strategies,the composites exhibited excellent catalytic properties,good electrical conductivity and stability,which provided design ideas and guidance for the construction of high current density OER catalysts.