Study And Application Of Cobalt-based Magnetic Nanomaterials

Cobalt-based nanomaterials have potential applications in the fields of high-density data storage,magnetic separation,and heterogeneous catalysis due to their combined magnetic and metallic functionality.In particular,the controllable synthesis of magnetic materials with specific structures and morphologies in the nanometer range can achieve excellent performance beyond that of bulk materials.At present,the research on cobalt-based hard magnetic materials mainly focuses on single rare earth permanent magnets,which limits its further development.Therefore,it is crucial to study and develop new cobalt-based magnetic materials and their composites to meet the applications of high-performance permanent magnet.In this paper,metal Co with different crystal structures,Co₂C/C and Co/Fe Co nanomaterials were prepared by liquid phase synthesis route.Its microstructure was optimized at the nanoscale exploiting magnetocrystalline and shape anisotropy,enabling hard magnetization of the material,and the synthesis of Sm₂Co₁₇/Co composite was explored.In addition,we also expanded the application of as-prepared materials in the field of electrocatalytic water splitting.The specific contents of the paper are as follows:1.Metal Co nanoparticles with controllable crystal structure were synthesized by the polyol reduction method,using cobalt acetate as the precursor and polyol as the solvent.By controlling the type of polyol,face-centered cubic(fcc)and hexagonal close-packed(hcp)Co particles were obtained,respectively.The effects of surfactants on the shape and dispersion state of Co nanoparticles were also investigated.With the increase of Na OH concentration,Co nanoparticles underwent the transformation from fcc phase to hcp phase,and the magnetic properties were greatly different with the content of the two phases.The sea urchin-like hcp Co in high magnetocrystalline anisotropy exhibits excellent hard magnetic properties with a coercivity as high as2891.5 Oe,while the spherical isotropic fcc Co exhibits soft magnetic properties with a saturation magnetization of 135.89 emu·g^-1.2.Orthorhombic Co₂C/C nanomaterials were synthesized by solution pyrolysis method using Co particles as precursors and different long-chain amines as solvents,and the optimal synthesis conditions were determined.It can be found that carbon-coated Co₂C nanoparticles can be obtained by thermally decomposing long-chain amines at 330°C,regardless of whether the precursor Co is fcc or hcp structure,and the morphology of the materials is related to the precursor Co.In addition,the Co₂C/C nanomaterial synthesized with hcp Co as growth template has higher magnetic anisotropy,the coercivity reaches 1300 Oe,and exhibits excellent hard magnetic properties.3.Co/Fe Co hard-soft magnetic composites with exchange coupling were prepared by combining polyol reduction method and electroless plating method.The magnetic properties of the composites show regular changes with the mass ratio of Co and Fe Co,and all materials exhibit single-phase ferromagnetic properties.Due to the uniform distribution of Fe Co phase on the surface of Co particles,the Co/Fe Co composite with a mass ratio of 1:2 has the strongest magnetic coupling effect,and the remanence is69.03 emu·g^-1,which is 21.9%higher than that of the single component,and the saturation magnetization is as high as 119.14 emu·g^-1,which fully proves the superiority of electroless plating.4.The Sm₂Co₁₇/Co composite was synthesized in situ by calcium reduction method.Through controlling the diffusion of the Sm/Co precursors during the high-temperature reduction process,a bulk composite with many stacked sheets was obtained,which has excellent ferromagnetic properties and a coercivity of 1431.6Oe.5.Finally,the application of Co and Co₂C/C nanomaterials in electrocatalytic water splitting was explored.It can be found that the oxygen evolution reaction(OER)activity of sea urchin-like hcp Co nanoparticles is significantly higher than that of spherical fcc Co nanoparticles with an overpotential of 279 m V@10 m A·cm^-2,while Co₂C/C exhibits excellent catalytic activity for the hydrogen evolution reaction(HER)with an overpotential as low as 73 m V@10 m A·cm^-2,which has potential as an efficient non-precious metal electrocatalyst.