Preparation And Properties Of Manganese Dioxide As Catalyst For Li Air Battery

Cathode catalyst is a decisive factor in the development of lithium air batteries.Most of the existing high efficiency catalyst are precious metal catalyst. However,precious metal is limited and expensive. Transition metal oxides as cathode catalysthas been widely concerned because it is cheap and easy to prepare. In this paper, wefocus on manganese oxide, cobalt oxide, cobalt oxide-manganese oxide compositeORR catalytic performance in neutral electrolyte.The air diffusion electrode is first selected as working electrode inelectrochemical tests. But the conductivity of air diffusion electrode is low. Besides,manual electrode repeatability is not good. We choose the catalyst modified glassycarbon electrode as the material testing electrode. The LSV curve appeared ORRcurrent pesk at around-0.6V, at which the current density represents the catalystperformance.In this paper, electrostatic spinning method is used to prepare manganesedioxide, and electric catalytic properties is studied. MnO2can not be abtainedthrough the electrostatic spinning method, so hydrothermal method is used toprepara manganese dioxide. Beta MnO2is prepared with ammonium persulfate asthe oxidant of hydrothermal method. Reaction temperature is120oC、140oC、160oCand180oC respectively, reaction time is6h、12h and24h respectively. When thereaction temperature is120oC, the material shows lowe XRD diffraction peak andthe morphology looks like blocks. Under the rest of the reaction temperature,materials are beta MnO2nanowires. When the reaction temperature is140oC andreaction time is12h, the best catalytic properties is abtained, the current density is29.07mA·cm-2. In order to compare catalytic properties of alpha MnO2and betaMnO2, manganese oxide is prepared with potassium permanganate as oxidant. Sameexperiments about reaction temperature and reaction time are carried out. Thematerial under the conditions of different temperature and time are alpha MnO2nanowires. As the extension of reaction time, the length of the material increase.The highest catalytic activity of alpha MnO2is obtained when the reactiontemperature is140oC and the reaction time of12h. When the electrode potential is-0.6V, current density reaches-34.5mA·cm-2. Through comparison, alpha MnO2hasa catalytic activity higher than that of beta MnO2. Select alpha MnO2for Co doping.Research on cobalt oxide is done before cobalt oxide doped alpha MnO2.Electrostatic spinning method is used to prepare Co3O4. After sintered at500oC,Co3O4is abtained, the current density of which is1.18mA·cm-2. Hydrothermalproducts are polygonal aggregate into block structure. In order to improve the hydrothermal product reunion phenomenon, PVP and PEG are used as dispersingagent respectively. PEG can change the morphology of the material, but the electriccatalytic properties of the material can not improve.The highest catalytic activity ofCo3O4is obtained when the reaction temperature is120oC and the reaction time of12h. When the electrode potential is-0.6V, current density reaches-3.74mA·cm-2.Compared with the product of electrostatic spinning method, the electric catalyticactivity of hydrothermal preparation Co3O4is higher. Nitric acid cobalt is adopted toalpha MnO2in hydrothermal method, the mole fraction is2%,5%and10%respectively. Energy spectrum test shows the proportion of Co and Mn in material iscorresponding to that of raw material doping ratio. But compared with alpha MnO2composite catalyst, the current density gets lower instead. Co3O4is directly added toalpha MnO2as catalyst, the current density also reduced. Neither doping nor mixedcatalyst improve the catalytic performance of materials.