| Supercapacitors, which are also called electrochemical Capacitors(ECs), are new storage energy devices in which the energy density is between traditional capacitors and traditional batteries. Supercapacitors show many advantages such as high power density, long lifecycle, rapid charging and discharging, environmental friendly, et al, so its application prospect is very wide. At present, it has already been applied in transportation, communications, aviation, consumer electronics and related research fields.Supercapacitor electrode materials are divided into three types which are conductive polymer materials, carbon-based materials, metal oxides and its hydrates. MnO2has attracted significant attention of researchers at home and abroad mainly due to cheap price, abundant raw materials and environment friendly. The forms of manganese oxide used for supercapacitors are divided into two categories, one is manganese oxide film, and the other is manganese oxide powder. There are a variety of preparation methods of manganese oxide, we can get various crystal manganese oxides with different electrochemical capacitor performances by using different preparation methods. The electrochemical deposition is the most widely applied method of preparation MnO2.Electrochemical Quartz Crystal Microbalances (EQCM), which use the piezoelectric effect of quartz crystal, changes the mass variation on electrode surface into the variation of frequency output signal in quartz oscillator circuit, the change of mass can be calculated using Sauerbrey formula, its measurement accuracy can reach the level of ng, so it is a kind of high sensitivity quality testing instruments. In the study, Pt wire as counter electrode, Ag/AgCl as reference electrode, with the quartz electrode plated gold form a three electrodes system. Different mass MnO2were deposited on the crystal electrode using linear scanning cyclic voltammetry electrodeposition method during0-1.6V in5mM MnSO4+0.1M Na2SO4, meanwhile EQCM recorded the variation of mass. The dynamic changes of the quality were studied using EQCM in situ during the charging and discharging process of MnO2, it was discussed that the effect of Li+、K+、Mg2+、NH4+、on electrochemical capacitor performance of MnO2. The cyclic voltammograms of14.00μg MnO2are all symmetrical rectangular about zero current line in0.1M Li2SO4during-0.25V-0.55V. The masses were decreased during the oxidation reaction process on active material surface as the deinsertion of cations, on the contrary, the masses were increased during the reduction reaction on active material surface as the insertion of cations, the former changes were equal to the latters. It proved that the supercapacitive charging/discharging mechanism of manganese dioxide concerned the reversible insertion/deinsertion of cations.The experiment researched the cyclic voltammetry performance of the same quality MnO2at different speeds and the variation of specific capacitance, respectively. The variations of different deposited mass MnO2were also studied on specific capacitance at different scan rates. The results show that the specific capacitance of certain quality MnO2reduce as the speed increasing; In a certain quality range, the specific capacitance decrease as deposition weight increasing.Cyclic voltammetry test of crystal electrode deposited MnO2indicated that specific capacitance decrease as the increasing of cationic radius in0.2M MgSO4,0.1M Li2SO4,0.1M K2SO4,0.1M (NH4)2SO4, MnO2displayed highest charge and discharge capacitance and good cycle properties in0.2M MgSO4. MnO2possess higher capacitance in electrolyte containing small radius and multivalent cations. |
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