Manganese oxides (MnOx) with various oxidation states and different nanostructures have recently received numerous attentions owing to their potential applications in many emerging fields such as catalysis, ion exchange, molecular adsorption, magnetic applications, secondary batteries and supercapac...
Manganese oxides (MnOx) with various oxidation states and different nanostructures have recently received numerous attentions owing to their potential applications in many emerging fields such as catalysis, ion exchange, molecular adsorption, magnetic applications, secondary batteries and supercapacitors. In this work, MnOx especially, Mn3O4 and mesoporous Mn2O3 nanostructures were synthesized by low temperature solution and hydrothermal process. In the first part, the controlled low temperature synthesis of Mn3O4 nanoparticles (NPs) and nanorods (NRs) using potassium permanganate, urea and cetyltrimethylammonium bromide (CTAB) were studied and performed the applications in electrochemical supercapacitors. The crystalline, quality and the morphological properties of the synthesized Mn3O4NPs and NRs were extensively analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), TEM, UV-Vis DRS, RAMAN and XPS. The influence of pH and reaction time on the transformation of Mn3O4 NPs to Mn3O4 NRs was thoroughly investigated. The nanostructures of Mn3O4 from NPs to NRs were dramatically changed with the increase of pH from 7 to 12 and reaction time from 12 to 48 h. It was found that Mn3O4 NRs morphology was obtained with pH – 12 and reaction time of 24 h. At low pH, highly dense and semispherical morphology of Mn3O4 NPs were observed with the average particle size of 20-30 nm, whereas at pH-12,the agglomeration of NPs resulted in the rods morphology which possesses the average diameter of50 nm and length of 600 nm. A growth mechanism was proposed on the basis of obtained results to describe the effects of the pH and reaction time in the morphology from NPs to NRs. The transformation of Mn3O4 NPs to NRs considerably increased the band gap from 2.37 eV to 2.43 eV, suggesting the good optical properties of synthesized materials. The synthesized Mn3O4NPs and NRs were used as electrode materials for the fabrication of electrochemical double layer supercapacitors (EDLCs). EDLCs with Mn3O4 NRs electrode with activated carbon (AC) showed the highest capacitance of 236 Fg-1 as compared to bare AC (170 Fg-1), bare Mn3O4 NPs (91 Fg-1), bare Mn3O4 NRs (110 Fg-1) and Mn3O4 NPs – AC (192 Fg-1) electrodes. Moreover, it also presented an excellent stability by maintaining ~ 90% of initial value after 1000 cycles, indicating the high stability of Mn3O4 NRs-AC electrode in organic electrolyte. The rod like morphology and AC might provide the good surface for the ions adsorption through the improved surface of electrode which might significantly accelerate the electron transportation and ion diffusion during the electrochemical process.
In the second part, the mesoporous Mn2O3 nanoparticles (NPs) were synthesized by a facile hydrothermal process using manganese acetate as precursor, citric acid as capping agent and sodium hydroxide at 150 oC and applied as electro-active materials for pseudo-capacitors. The morphology and surface analysis deduced the mesoporous nature of synthesized Mn2O3 NPs. The synthesized materials were thoroughly characterized in terms of structural, crystalline, composition, surface and electrochemical properties by XRD, field-emission SEM, high-resolution TEM, N2adsorption/desorption isotherm measurements, X-ray photoelectron spectroscopy (XPS), and multi cycles CV and EIS.From Mn 2p XPS results, the spin-orbit splitting value of Mn 2p3/2 and Mn 2p1/2 was estimated about 11.8 eV, which was very close to reported values for Mn2O3, confirming the formation of Mn2O3 NPs without exiting other oxide forms.The synthesized mesoporous Mn2O3 NPs were coated on Ni foam to fabricate the pseudo-capacitors and the performance was evaluated in alkaline electrolyte (6M KOH). Mesoporous Mn2O3 NPs based electrode showed high specific capacitance of 460 F g−1 at scan rate of 10 mVs-1 and possessed the good cycling stability after 25 cycles. The excellent capacitance was resulted from the mesoporous nature, high surface area of electrode, and low diffusion resistance, leading the fast ions transportation and reduction in the ion diffusion length over the surface of Mn2O3 NPs electrode.
Manganese oxides (MnOx) with various oxidation states and different nanostructures have recently received numerous attentions owing to their potential applications in many emerging fields such as catalysis, ion exchange, molecular adsorption, magnetic applications, secondary batteries and supercapacitors. In this work, MnOx especially, Mn3O4 and mesoporous Mn2O3 nanostructures were synthesized by low temperature solution and hydrothermal process. In the first part, the controlled low temperature synthesis of Mn3O4 nanoparticles (NPs) and nanorods (NRs) using potassium permanganate, urea and cetyltrimethylammonium bromide (CTAB) were studied and performed the applications in electrochemical supercapacitors. The crystalline, quality and the morphological properties of the synthesized Mn3O4NPs and NRs were extensively analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Field Emission Scanning Electron Microscopy (FESEM), TEM, UV-Vis DRS, RAMAN and XPS. The influence of pH and reaction time on the transformation of Mn3O4 NPs to Mn3O4 NRs was thoroughly investigated. The nanostructures of Mn3O4 from NPs to NRs were dramatically changed with the increase of pH from 7 to 12 and reaction time from 12 to 48 h. It was found that Mn3O4 NRs morphology was obtained with pH – 12 and reaction time of 24 h. At low pH, highly dense and semispherical morphology of Mn3O4 NPs were observed with the average particle size of 20-30 nm, whereas at pH-12,the agglomeration of NPs resulted in the rods morphology which possesses the average diameter of50 nm and length of 600 nm. A growth mechanism was proposed on the basis of obtained results to describe the effects of the pH and reaction time in the morphology from NPs to NRs. The transformation of Mn3O4 NPs to NRs considerably increased the band gap from 2.37 eV to 2.43 eV, suggesting the good optical properties of synthesized materials. The synthesized Mn3O4NPs and NRs were used as electrode materials for the fabrication of electrochemical double layer supercapacitors (EDLCs). EDLCs with Mn3O4 NRs electrode with activated carbon (AC) showed the highest capacitance of 236 Fg-1 as compared to bare AC (170 Fg-1), bare Mn3O4 NPs (91 Fg-1), bare Mn3O4 NRs (110 Fg-1) and Mn3O4 NPs – AC (192 Fg-1) electrodes. Moreover, it also presented an excellent stability by maintaining ~ 90% of initial value after 1000 cycles, indicating the high stability of Mn3O4 NRs-AC electrode in organic electrolyte. The rod like morphology and AC might provide the good surface for the ions adsorption through the improved surface of electrode which might significantly accelerate the electron transportation and ion diffusion during the electrochemical process.
In the second part, the mesoporous Mn2O3 nanoparticles (NPs) were synthesized by a facile hydrothermal process using manganese acetate as precursor, citric acid as capping agent and sodium hydroxide at 150 oC and applied as electro-active materials for pseudo-capacitors. The morphology and surface analysis deduced the mesoporous nature of synthesized Mn2O3 NPs. The synthesized materials were thoroughly characterized in terms of structural, crystalline, composition, surface and electrochemical properties by XRD, field-emission SEM, high-resolution TEM, N2adsorption/desorption isotherm measurements, X-ray photoelectron spectroscopy (XPS), and multi cycles CV and EIS.From Mn 2p XPS results, the spin-orbit splitting value of Mn 2p3/2 and Mn 2p1/2 was estimated about 11.8 eV, which was very close to reported values for Mn2O3, confirming the formation of Mn2O3 NPs without exiting other oxide forms.The synthesized mesoporous Mn2O3 NPs were coated on Ni foam to fabricate the pseudo-capacitors and the performance was evaluated in alkaline electrolyte (6M KOH). Mesoporous Mn2O3 NPs based electrode showed high specific capacitance of 460 F g−1 at scan rate of 10 mVs-1 and possessed the good cycling stability after 25 cycles. The excellent capacitance was resulted from the mesoporous nature, high surface area of electrode, and low diffusion resistance, leading the fast ions transportation and reduction in the ion diffusion length over the surface of Mn2O3 NPs electrode.
주제어
#Manganese oxide Nanoparticles Nanorods Mesoporous Supercapacitor Electrochemical properties
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