Preparation And Application Of Polypyrrole And Co Sulfide On Core-Shell Nanoarrays Electrodes In Supercapacitor

With the increasing of energy crisis and environmental problems,the development of electrochemical energy storage devices has become the key to solve these problems.In recent years,supercapacitors have attracted wide attention owing to their higher power density and longer cycle life than the conventional batteries and capacitors.However,the lower energy density has hindered their applications,the energy density of supercapacitor can be increased by enhancing the specific capacitance of the electrode.In recent years,conductive polymer and metal sulfide have been favored by researchers,but poor stability of conductive polymer and poor conductivity of metal sulfide have limited their development.In this paper,core-shell structure of electrodes based on polypyrrole and cobalt-based sulfide were prepared on nickel foam.Then the asymmetric supercapacitors were assembled using core-shell electrode as the positive electrode and carbon nanotubes or active carbon as negative electrode.The content includes two parts:The PPy@CoS core-shell nanowire electrode was obtained by using a two-step electrodeposition on the nickel foam substrate.As a conductive skeleton,the PPy nanowires contribute to the conductivity of the materials and shorten the ion diffusion pathway.The CoS nanosheets work as a protective layer to effectively avoid the volume shrinkage of the PPy skeleton during the charge and discharge process.The core-shell nanostructure owns a large surface area,rich active sites,and good structural stability.The obtained PPy@CoS electrode yields a high specific capacitance of 2191 F g-1 at a current density of 1 A g-1 and the capacitance is increased,123%of initial capacitance is obtained instead of declining after 3000 cycles.By comparison,we know the PPy@CoS electrode performs better than single electrodes of PPy or CoS in conductivity,capacitance and cycle stability.To test the practical value of electrode,we have further assembled the PPy@CoS//CNT asymmetric supercapacitor devices(the power density yields 174.8 W Kg-1 at the energy density of 48.6 Wh Kg-1).Finally,we have connected two devices in series to power a red LED.The CoS and MnCo2S4 nanowire electrodes with core-shell nanostructure were grown by a two-step hydrothermal method on the nickel foam substrate.By comparing their performance,we know the MnCo2S4 electrode owns better electrochemical performance,and it yields a specific capacitance of 2507 F g'1 at the current density of 1 A g-1,29.4%higher than the CoS,and outstanding cycling stability(8.3%loss after 2000 cycles).This is mainly due to the Mn-Co bimetallic synergy,which provides better electrical conductivity and more active sites.In order to test its application capability,we have also assembled the MnCo2S4//AC asymmetric supercapacitor devices(the power density yields 750.4 W Kg-1 at the energy density of 49.5 Wh Kg-1),and a white LED has been powered by two devices in series.