Preparation And Electrochemical Properties Of Transition Metal Manganese And Iron Oxide-based Composite Materials

As the national development strategy of"carbon peaking and carbon neutrality"（double carbon for short）is put forward,China’s emerging renewable energy is developing rapidly.Among them,the use of emerging renewable energy to generate power becomes one of the more feasible ways to achieve the dual-carbon goal today.The research and exploitation of energy storage equipment also has surely attracted great attention from researchers in China and all over the world.Among all kinds of energy storage devices,supercapacitors stand out with various advantages,attaching widespread attention of scientists.The selection of electrode materials remains one of the main factors affecting the electrochemical properties of supercapacitors.Owing to their low price,abundant reserves,environmental friendliness,and diverse valence states,transition metals manganese and iron have become current research hotspot.In view of this,this research work will be carried out from the following aspects:1.Preparation and electrochemical properties of MnO@NC compositeUsing carboxymethyl chitosan as the nitrogen source and carbon source;potassium permanganate as the only manganese source,simultaneously as a strong oxidant,MnO and nitrogen-doped carbon composite（MnO@NC）was successfully prepared by techniques containing water bath heating,freeze drying,high temperature carbonization.The physical properties of the materials were characterized and analyzed by XRD,Raman,SEM,TEM and XPS while the effects of KMnO₄/carboxymethyl chitosan dosage ratio on the morphology,structure and properties of the products were also investigated.The results indicated that its specific capacitance reached 326.36 F g^-1at 0.5 A g^-1,and after 10,000 cycling at 1 A g^-1,the capacitance remained the 60%of the initial value.When assembling MnO-NC-0.05 and activated carbon（AC）into MnO-NC-0.05//AC asymmetric supercapacitor device,the energy density was 9.35 Wh kg^-1when the power density reached 374.83 W kg^-1.After 10000 charge-discharge cycles at 3 A g^-1,the capacitance retained 172%,showing an excellent cycle stability.2.Preparation and electrochemical properties of Fe₃O₄@MnO₂-HNSFirst,SiO₂nanospheres were prepared by the St（?）ber method,then ferrocene was applied as Fe source and H₂O₂was adopted as strong oxidant to synthesize Si O₂@Fe₃O₄@C.KMnO₄was chosen as Mn source to prepare Si O₂@Fe₃O₄@MnO₂via a hydrothermal method.Finally,Si O₂@Fe₃O₄@MnO₂was etched into a double-shell hollow structure（Fe₃O₄@MnO₂-HNS）using Na OH.Characterization methods such as XRD,SEM,TEM,and XPS were conducted to analyze its phase and structure.Electrochemical test results demonstrate that Fe₃O₄@MnO₂-HNS exhibits excellent performance,reaching a specific capacitance of 375.14 F g^-1at 0.5 A g^-1in three-electrode system.When paired with AC as a device,70.6%of the initial capacitance can still retain after 5000 cycles at 2 A g^-1.3.Preparation and electrochemical properties of Mn Fe-MOF derived materialsMnFe-MOF was obtained by coordinating 2-methylimidazole with Mn and Fe derived from Mn（NO₃）₂·4H₂O and Fe（NO₃）₃·9H₂O,respectively,following by pyrolysis at high temperature to eventually prepare Mn₃O₄-Fe₂O₃-NC.Mn₃O₄-Fe₂O₃-NC exhibits good electrochemical properties,presenting a maximum specific capacitance of 660 F g^-1at 1 A g^-1.In the Mn₃O₄-Fe₂O₃-NC‖AC two electrode construction,the capacitance remains 85.4%of the initial value after 3000 cycles at 6 A g^-1,proving its good cyclicity.4.Preparation and electrochemical properties of Fe₃O₄@Fe₂P heterostructureFe₃O₄was primarily synthesized by using FeCl₃·6H₂O as the only iron source and glycol as solvent,then Fe₃O₄@Fe₂P heterostructure were achieved by solid-phase phosphating at low temperature.It can reach a high specific capacitance of 651.25 F g^-1at 0.5 A g^-1in the three-electrode system,and exhibited ultra-high power density,energy density and ultra-stable cycling performance in the Fe₃O₄‖AC double electrode system.When the power density is 424.98 W kg^-1,its energy density remains 13.47 Wh kg^-1,and it maintains 78.5%of the initial value of capacitance after 5000 cycles at 6 A g^-1.