Study On Nano-morphological Regulation And Electrochemical Properties Of Manganese-based Dioxides

Manganese dioxide?MnO₂?that is used as electrode materials of supercapacitor and water electrolysis has the advantages of low cost,abundant resources,easy synthesis and environment friendliness,but it has the problems of poor conductivity,low utilization rate,high oxygen evolution potential and poor catalytic activity.Five kinds of MnO₂ with different morphologies?i.e.,nanospheres,nanosheets,nanoflowers,nanorods,doped ultra-thin nanosheets?were anodically electrodeposited on the substrate of CFP?carbon fiber paper?by adjusting metal-ion-doping,H2SO4 concentration and deposited current density.The morphologies,structure and performances of MnO₂ nano-composite electrodes for capacitance and OER?oxygen evolution reaction?were investigated by FESEM?field emission scanning electron microscopy?,TEM?transmission electron microscopy?,XRD?X-ray diffraction?,XPS?X-ray photoelectron spectroscopy?and related electrochemical techniques.The results show that MnO₂ with different morphologies?i.e.,nanospheres,nanosheets,nanopflower and nanorods?can be fabricated on the CFP using a facile method of anodic electrodeposition by adjusting the H2SO4 concentration and the deposited current density.When the GV charging-discharging rate is 0.5 A g-1,four kinds of composite electrodes with MnO₂ nanospheres,MnO₂ nanosheets,MnO₂ nanoflowers and MnO₂ nanonods had a relatively high specific capacitance?areal capacitance?of 134.4 F g-1?0.20 F cm-2?,226.3 F g-1?0.33 F cm-2?,235.6 F g-1?0.35 F cm-2?and 362.5 F g-1?0.54 F cm-2?,respectively.The specific capacitance of MnO₂nanorod/CFP composite decreased from 362.5 F g-1?0.54 F cm-2?to 160.0 F g-1?0.24 F cm-2?when the GV charging-discharging rate increased from 0.5 to 5 A g-1,which is a relatively high retention of the original capacitance?i.e.,44.1%?.Various morphologies of MnO₂/CFP composite electrodes retained more than 95% and 90%of the initial capacitance after 5000 cycles at 5 A g-1under flat and bent states respectively,showing excellent cycle stability.The metal-ion?Fe,V,Co and Ni?-doped MnO₂ high-density nano-clusters that consist of ultra-thin nanosheets with a thickness of approximately 5 nm was obtained on the CFP using a facile method of anodic electrodeposition by adjusting the H2SO4 concentration,the deposited current density and metal-ion-doping.The metal-ion?i.e.,Fe,V,Co,and Ni?has been doped into bulk MnO₂,improving the conductivity.The metal-ion?Fe,V,Co and Ni?-doped MnO₂ ultrathin nanosheet/CFP and the Ir O2/CFPcomposite electrodes for OER achieved a low overpotential of 390 mV and 245 mV to reach 10 mA cm-2in 1 M KOH,respectively.However,the oxygen evolution overpotential of the pure MnO₂/CFP composite electrode is 467 mV.The overpotential of the doped composite electrode for long-term OER at a constant current density of 20 mA cm-2was much lower than that of the pure MnO₂ composite electrode.