| The Mn3O4 only has hausmannite structure at room temperature,of which pure phase can be easily made.Mn3O4 nanoparticles have small size effect,quantum effect,surface effect,interface effect and macroscopic quantum tunnel effect.As a result,the magnetic performances,electrochemical performances and catalytic activity of Mn3O4 nanoparticles are more excellent,and thus they become the research focus of Mn3O4 materials.The preparation of nano Mn3O4 with small size and high purity is crucial to the improvement of its magnetic performances.The nano Mn3O4 electrode materials with higher surface area and good conductivity are an important research direction in the field of supercapacitor.At present,there are many methods of preparing nano Mn3O4-based materials.There are many problems about the preparation of nano Mn3O4-based materials,such as high cost and environmental pollution caused by using KMn O4 or other oxidants,organic acid manganese salt and organic solvents.In addition,there are many disadvantages of complex synthesis process,high energy consumption and difficulty in controlling the products.In this paper,a facile method i.e.ion diffusion controlled by ion exchange membrane was used for synthesizing Mn3O4 nanomaterials with high purity and its binary cooperative complementary M(OH)n/Mn3O4(M=Cr,Co,Al,Ce)nanocomposites.X-ray diffraction(XRD),scanning electron microscopy(SEM),transmission electron microscopy(TEM),X-ray photoelectron spectroscopy spectrum(XPS)and N2 adsorption-desorption test(BET)were conducted to understand the morphology,structure,formation process and composites of as-prepared nano Mn3O4.Electrochemical performance of the as-prepared electrode materials were studied by electrochemical workstation and magnetic performances of nano Mn3O4 were studied by magnetic property measurement system(MPMS-XL-7).The detailed works are as follows:(1)A series of nano Mn3O4 have been successfully prepared using MnSO4·H2O and NaOH as reactants at different reaction temperatures.The effects of reaction and annealing temperature on the morphology,structure,electrochemical properties and magnetic properties of the products were studied by various modern analytical tools.The results show that the structure and properties of Mn3O4 nanomaterials are closely related to the reaction and annealing temperature.With the increase of reaction temperature,the particle size of Mn3O4 nanomaterials increases gradually and the morphology changes from irregularly flaky particles into octahedral structure with eight highly stable{111}faces(90?).When Mn3O4nanomaterials were annealed under 330?,there was a significant change in the morphology.The nano Mn3O4 prepared at 90?exhibit a highest specific capacitance of 124 F g-1 at a current density of 0.5 A g-1,and the electrochemical performance of samples become poorer after annealing.The Mn3O4 nanomaterials prepared at 30?with small particle size(20?80nm)has the best magnetic performances,the saturation magnetization(Ms),remanent magnetization(Mr)and coercive force(Hc)are29.3 emu g-1,18.5 emu g-1 and 4360 Oe respectively.With the increase of reaction temperature,the size of nano Mn3O4materials gradually increases and the values of Ms,Mrand Hc gradually decrease.(2)The binary cooperative complementary M(OH)n/Mn3O4 nanocomposites using MnSO4·H2O,Co(NO3)2·6H2O,Cr(NO3)3·9H2O,Al2(SO4)3·18H2O,Ce(NO3)3·6H2O and NaOH as reactants were prepared by one step at room temperature under normal pressure.The effects loading different metal ions on the morphology,structure and properties of Mn3O4 nanomaterials were explored.The results show that Mn3O4 crystal particles are uniformly oriented in a particular direction and the surface free energy can be reduced.Thus the morphology of products became looser,which can lead to greater specific surface area and pore volume.At the same time,loading other metal ions will enhance the electrical conductivity and finally improve the electrochemical performances of the samples.The specific capacitances of Cr(OH)3/Mn3O4,Co(OH)2/Mn3O4,Al(OH)3/Mn3O4 and Ce(OH)3/Mn3O4 electrode materials at a current density of 0.5 A g-1 are 156,174,154 and174 F g-1 respectively.The electrochemical performances of all the electrodes are better than that of Mn3O4 nanomaterial(98 F g-1)prepared under the same condition.(3)The binary synergistic Co(OH)2/Mn3O4 nanocomposites loading different concentration of Co2+were successfully prepared by one step at room temperature under normal pressure.The results show that the generated Co(OH)2 nanoparticles in the process of reaction can adsorb on the surface of nano Mn3O4through hydrogen bonding and vander Waals force,which self-assembly to form Co(OH)2/Mn3O4 nanocomposites.The agglomeration state of nano Mn3O4 is significantly improved,and which is favorable to form mesoporous structure.The molar ratio of Co2+/Mn2+in the reactants affects the morphology,crystallinity,specific surface,pore distribution and electrochemical performance of Co(OH)2/Mn(OH)2 nanocomposites.When the molar ratio of Co2+/Mn2+is3%,the Co(OH)2/Mn3O4 nanocomposites have greater surface area of 57.55 m2 g-1 and the highest capacitance of 214 F g-1 at a current density of 0.5 A g-1,which is 118%higher than that of Mn3O4 nanomaterials.The capacitances of Co(OH)2/Mn3O4 nanocomposites are better than that of pure Mn3O4and Co(OH)2,and also far higher than Co(OH)2 and Mn3O4 materials mechanically mixed with the same Mn/Co mole ratio prepared under the same methods and conditions.In addition,it is also found that the Co2+can inhibit the oxidation of Mn2+to a certain extent,improve the stability of the electrode materials and reduce the charge transfer resistance of the Mn3O4 electrode/electrolyte interfaces.All the results indicate that there is a synergistic effect between Co(OH)2 and Mn3O4 nanoparticles. |
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