The Preparation Of Cobalt Metal Organic Framework And Its Derivatives And Their Application In Oxygen Evolution Reaction

The design and synthesis of high-efficiency electrocatalysts are very important in the field of electrochemical energy conversion,and the oxygen evolution reaction(OER)is a key process in this conversion.In recent years,metal organic framework(MOF)materials have attracted extensive attention as advanced electrocatalysts for electrochemical energy conversion due to their good physical and chemical stability,high surface area and adjustable chemical structure.In this thesis,hydrothermal method and calcination method were used to synthesize cobalt metal organic framework(Co-MOF)nanosheets,nitrogen-doped cobalt oxide(N-Co3O4)and cobalt nanoparticles/nitrogen-doped carbon composites(Co/N-C)sythesized using Co2+as the metal source and different organic ligands.The eletrocatalytic OER properties of this series of materials were investigated.Specifically,it includes the following three parts:1.Using a surfactant-assisted one-step hydrothermal method,we prepared a two-dimensional uitrathin Co-MOF nanosheets(Co2(OH)2BDC,BDC = 1,4-phthalic acid)with good catalytic activity by coordinating self-assembly of cobaltous nitrate hexahydrate with 1,4-phthalic acid.The electrocatalyst exhibited excellent electrocatalytic OER performance in 1.0 M KOH:at 10 mA cm-2,the overpotential was 263 mV,and the Tafel slope was as low as 74 mV dec-1.Before and after electrocatalysis,the morphology and structure of the material did not change significantly,and the electrocatalytic OER activity above 12000 s was maintained.The unsaturated Co? active sites exposed on the surface of ultrathin two-dimensional Co-MOF nanosheets enhance the catalytic activity of OER.2.One-dimensional Co-MOF materials were prepared by the reaction of cobaltous nitrate hexahydrate with 4,4'-bipyridine and 1,3,5-benzenetricarboxylic acid under solvothermal conditions.The N-Co3O4 materials with different structures were prepared by calcining Co-MOF at different temperatures in air atmosphere.The effect of different structures of N-Co3O4 materials on the catalytic properties of OER were studied.The results show that the mesoporous N-Co3O4 obtained by calcination at 600? exhibits better electrocatalytic performance.When the current density reaches 10 mA cm-2,the required potential is 1.548 V and the Tafel slope is 99 mV dec-1.3.Two Co-MOFs were prepared by solvothermal method by changing the feed ratio of cobaltous nitrate hexahydrate,4,4'-bipyridine and 1,3,5-benzenetricarboxylic acid.The Co/N-C composites with different morphologies were obtained by calcination under the nitrogen atmosphere with these two Co-MOF precursors.The effects of the morphology of the composites on the electrocatalytic OER activity were investigated.The electrochemical tests show that the Co/N-C composite with core-shell structure has an overpotential of 207 mV and a Tafel slope of 74 mV dec-1,which is superior to the non-core-shell Co/N-C composite(overpotential is 333 mV),and long-term durability after 2000 cycles of cyclic voltammetry.The excellent OER properties of Co/N-C composite are attributed to the synergistic effect of cobalt nanoparticles and nitrogen-doped carbon components,as well as the special core-shell structure,which promotes charge transfer at the catalytic interface and facilitates proton transport.