Cast Oxidation Of Manganese Dioxide Manganese Preparation And Electrochemical Performance Of Porous Materials

This paper mainly consists of three sections, review, experiments and electrochemical measurements of the fabricated materials. The synthesis methods, properties, applications, and development of porous manganese oxide crystals were reviewed in terms of the structural characteristics of porous manganese oxide crystals in the first section (Chapter 1). The two synthesis methods of a new MnO₂-pillared porous manganese oxide with a layered structure were described in the experiments section (Chapter 2, and 3), in which layered manganese oxide was acted as precursor and manganese oxide was acted as pillaring agent. We adopted the samples obtained at different stages by exfoliation/reassembling method to study and characterize their structures and electrochemical properties (Chapter 4).An ion-exchange/intercalation method for synthesizing a new MnO₂-pillared porous manganese oxide with a layered structure was described in Chapter 2. H-type layered manganese oxide was obtained by an acid exchange mechanism from its Na-type precursor, which was synthesized by the oxidation precipitation method in sodium hydroxide solution. H-type layered manganese oxide was reacted with Mn²⁺ ions, Mn²⁺ ions were able to be intercalated into the interlayer of H-type layered manganese oxide by an ion-exchange mechanism. The Mn²⁺ intercalated layered manganese oxide was then soaked in a mixed solution of NH₃·H₂O + H₂O₂, the Mn²⁺ ions existed in the interlayer was oxided to MnO₂, and MnO₂ pillared layered manganese oxide was obtained. A MnO₂ pillared mesoporous manganese oxide with a broken layered structure and had a basal spacing of 0.66 nm was obtained by heating the MnO₂ pillared manganese oxide in the air at 200℃for 3 h. The effect of Mn²⁺ ions with different concentrations on the structure and property of Mn²⁺ pillared porous materials was examined. The results showed that the ion-exchange/intercalation procedure was a method of preparing porous manganese oxide materials but not the best one; the prepared materials had poor crystallinity and thermal stability by this method. The obtained materials at different stages were characterized by XRD, DSC-TGA, SEM, IR and AAS.An Exfoliation/Reassembling method for synthesizing a new MnO₂-pillared porous manganese oxide with a layered structure was described in Chapter 3. A delaminated well-dispersed manganese oxide nanosheet suspension was obtained by soaking H-type layered manganese oxide in an aqueous solution of tetramethylammonium hydroxide (TMAOH) for 7 days. The colloidal suspension was reassembled with Mn²⁺ ions to obtaine Mn²⁺ intercalated layered manganese oxide. The Mn²⁺ intercalated layered manganese oxide was then soaked in a mixed solution of NH₃·H₂O+H₂O₂, MnO₂ pillared layered manganese oxide was obtained. The MnO₂ pillared layerd manganese oxide was calcined at 200℃for 3 h in the air, a MnO₂ pillared mesoporous manganese oxide was obtained, which still maintained a layered structure and had a basal spacing of 0.69 nm as well as a BET area of 116 m²/g. The effect of Mn²⁺ ions with different concentrations on the structure and property of the MnO₂ pillared porous materials was examined. The results showed that the exfoliation/reassembling procedure is a more effective method for preparing porous manganese oxide materials, and the fabricated materials had good crystallinity and thermal stability by this method. The obtained materials at different stages were characterized by XRD, DSC-TGA, SEM, IR, AAS and N₂ adsorption-desorption and element analysis.By a CV test method, we investigated the electrochemical properties of the fabricated materials in Chapter 2 and Chapter 3. The results indicated that the calcinated temperature had a large effect on the the structure and electrochemical performance of the obtained materials. The sample MnO₂ pillared mesoporous manganese oxide by heating at 300℃for 3 h had a better electrochemical performance, which showed a larger specific capacitance of 200 F/g in 1mol/L Na₂SO₄ electrolyte at a scan rate of 5 mV/s. Moreover, the electrode showed high electrochemical stability and a long cycle life indicating a promising material for supercapacitors.