Electrochemical Performance Of Polypyrrole-based Mixed Metal Oxides Composite Nanomaterials

Supercapacitors are currently widely investigated due to their interesting characteristics in terms of high power density, long cycle life, short charging times, and good reversibility. Compared with the traditional electrode materials such as IrCl3, RuCl3, RuO2, MnO2, In2O3, et al, polypyrrole(PPy) is one of the most promising electrode materials for supercapacitors because of its advantages of good flexibility, high conductivity, facile preparation, easy control, good biocompatibility, and environment friendly. However, large volumetric swelling and shrinking during charge/discharge process as a result of ion doping and dedoping. This volumetric alternation often leads to structural breakdown and thus fast capacitance decay of conducting polymers. The relatively poor cycling stability limits the application of the PPy.Based on above analysis, to realize the high capacitance, high energy density, excellent cycling-life in a PPy-based composite material, the dissertation has constructed a series of composite nanostructures containing PPy and binary metal oxides with advantages of multi-valence, high capacitance and excellent cycling-life. We have investigated the effect of structure and ions in binary metal oxides on electrochemical properties and explored the structure-properties relationship through analysis of the mechanism of the electrochemical reaction, and major results are described as following:We have designed NiMoO4/PPy core-shell composite nanostructures for high-performance supercapacitors. The specific capacitance, rate capability, and cycling ability of the NiMoO4/PPy are obviously better than that of the bare NiMoO4 and PPy. When used as electrodes in supercapacitors, the composite nanostructures demonstrated prominent electrochemical performances with a high specific capacitance(1 389 F/g at a current density of 5 mA/cm2), a high areal capacitance(2.98 F/cm2 at a current density of 5 mA/cm2). The good cycle stability(71% capacitance retention after 1 000 circles at a current density of 8 mA/cm2) is better than PPy(44%). The charge&transfer resistance of the NiMo O4/PPy is obviously smaller than that of the bare NiMoO4 and PPy.We have designed NiCo2O4/PPy core-shell composite nanostructures on carbon fiber. When used as electrodes in supercapacitors, the composite nanostructures demonstrated prominent electrochemical performances with a high specific capacitance(1 328 F/g at a current density of 2 mA/cm2), a good cycling ability(85% of the initial specific capacitance remained after 5 000 cycles at a high current density of 10 mA/cm2), and a good rate capability(80.4% when the current density increases from 2 to 20 mA/cm2). The specific capacitance, rate capability, and cycling ability of the NiCo2O4/PPy are obviously better than that of the bare NiCo2O4 and PPy.We have designed three-dimensional hierarchical ZnCo2O4/PPy composite nanostructures on Ni foam. When used as electrodes in supercapacitors, the composite nanostructures demonstrated prominent electrochemical performances with a high specific capacitance(1 559 F/g at a current density of 2 mA/cm2), a good cycling ability(90% of the initial specific capacitance remained after 5 000 cycles at a high current density of 10 mA/cm2), and a good rate capability(89% when the current density increases from 2 to 20 mA/cm2). The specific capacitance, rate capability, and cycling ability of the ZnCo2O4/PPy are obviously better than that of the bare ZnCo2O4 and PPy. Moreover, the high energy density is 30.9 Wh/kg at a current density of 2 mA/cm2 in a two-electrode system.