Fabrication Of Cobalt Metal-Organic Framewok Microflowers And Their Application In Oxygen Evolution Reation

Metal-organic frameworks(MOFs),a new class of crystalline porous organic-inorganic hybrid materials,exhibit highly porous structures that span over a large range of pore sizes(micro-or mesopores)or pore shapes(cages and channels),which make MOFs have advantages in ultrahigh surface area,more unsaturated active sites,lower material density,and easily for further modification.MOFs achieved worldwild interest over the past two decades and are widely applied in the fields of gas adsorption and separation,sensing,biomedicine,energy storage and release,and catalysis.Among various morphologies of MOFs,the MOFs in the shape of flower have gradually attracted scientists’ attention.Micro/nanoflowers are micro/nanoparticles formed by self-assembly nanosheets.The fully exposed nanosheets enable micro/nanoflowers to have a higher specific surface area,more active sites,and mesopores or micropores for charge transport,leading micro/nanoflowers having potential application in the fields of catalysis,sensing,and energy storage and release.It can be foreseen that combining MOFs materials with micro/nanoflowers will result in materials with superior performance,which are worth of more reaserches.In this paper,a well-formed Co-MOF microflowers were synthesized by a simple room temperature precipitation method.During the experiment,the metal ion solution was dropped into the surface of the organic ligand solution to form two-dimensional nanosheets in the horizontal direction.Under suitable experimental conditions,the nanosheets were further cross to form a morphology of flower.We successfully synthesized cobalt metal-organic framework microflowers by changing organic ligands,reaction concentration,reaction humidity,dropping order and ratio,and stirring speed.The morphology,composition,crystal structure,thermal stability,and surface area of microflowers were characterized and analyzed by SEM,FT-IR,XRD,TG and BET.The experimental results show that the synthetic microflowers are layered structures assembled by smooth surface nanosheets with regular morphology and the crystal structure of Co-MOF-71,being well in monodispersity and thermal stability.Electricity-driven water splitting to produce hydrogen fuels and oxygen is one of the most promising strategies for converting electrical energy into chemical energy.Hydrogen,an efficient and sustainable clean energy.is the most potential candidate for solving energy problems.The water-splitting reaction can be classified into two half reactions:hydrogen evolution reaction(HER)and oxygen evolution reaction(OER).Because of four-electron transfer processes with removing four protons from water molecules to produce an oxygen molecule,OER has sluggish oxygen evolution kinetics requiring a large overpotential to promote the reaction,which hamper further application of hydrogen on industrial scale.At present,most OER electrocatalysts are transition metal oxides,hydroxides and nitrogen-containing compounds,etc.However,few MOFs are directly applied into the oxygen evolution reaction,mostly are corresponding derivatives synthesized by using MOFs as a template.We applied the synthesized Co-MOF microflowers into the oxygen evolution reaction and compared it with the bulk Co-MOF synthesized by solvothermal.It was found that the catalytic activity of Co-MOF microflowers were better than the bulk Co-MOF,which proved that the structure and morphology of the MOFs microflowers determine their ability to be a good OER electrocatalyst.Furthermore,the catalytic performance of Co-MOF microflowers and their derivatives were explored.Among them,the catalytic activity of Co-MOF microflowers/copper foil was satisfied,and it had potential for further development and application.