Design,Preparation And Electrochemical Characterization Of Co-based Compounds/Carbon Electrodes For Supercapacitor Applications

Supercapacitors with the characteristics of high power density,fast charge-discharge,long life time,etc.play an important role in energy storage and energy management.Among a diversity of electrode materials,Co-based compounds become one kind of promising supercapacitor electrode materials due to their advantages of high theoretical capacitance,low cost and environmental friendliness.However,there still remain some critical challenges in practical applications for Co-based compounds,such as poor conductivity,cycling stability and rate capability.In this paper,excellent supercapacitive behaviors have been achieved especially cycling stability at high current densities by optimization of cobalt-based compounds microstructure combined with advanced carbon materials/structures.The main contents and results of this paper are as follows:1.We introduce facile synthesis of interconnected Co₃O₄ nanosheets anchored on reduced graphene oxide?rGO?-coated nickel foam?NF?,i.e.Co₃O₄/rGO/NF composite electrode.Further investigation reveals that comparing to Co₃O₄ nanosheets prepared directly on the NF surface,the Co₃O₄/rGO/NF composite electrode has higher sheet density and thinner thickness of Co₃O₄nanosheets and higher specific surface area and more optimal mesoporous size.The rGO and thinner Co₃O₄ nanosheets improve electrical conductance,relief volume of active material expansionary and benefit strain relaxation during the charge and discharge,thus significantly prompting the supercapacitive behaviors.A specific capacitance of¹016.4 F g^–1 is achieved for the Co₃O₄/rGO/NF electrode at the current density of 1.0 A g^–1,much larger than Co₃O₄/rGO(?520.0F g^–1).Meanwhile,the Co₃O₄/rGO/NF electrode exhibits excellent stability at a high current density of 7.0 A g^–1 and retains⁹5.5%of the initial value even after 3000 charge-discharge cycles,which is significantly higher than that of Co₃O₄/NF?⁸4.4%?.2.A free-standing electrode structure composed of multilayered Co₉S₈ nanosheets wrapped by carbonized poly?3,4-ethylenedioxythiophene?:poly?styrene sulfonate?/rGO layers is introduced.Excellent supercapacitive behaviors,especially long cycling stability at high current densities are delivered owing to the synergetic effects of stable electrical contact between the active material and carbonized PEDOT:PSS/rGO due to the wrapped configuration,efficient charge exchange between the multilayered Co₉S₈ plates and electrolyte,improved electrical conductance by rGO,and plenty of voids for accommodating volume changes.For the optimized electrode?0.5 cP/rGO/Co₉S₈?,a specific capacitance of⁷88.9 F g^–1 at 1.0 A g^–1 and good cycling stability of over 100%of the initial capacitance(⁴88.6 F g^–1)after 10000 cycles at a current density of 15.0 A g^–1 can be achieved.The assembled asymmetric supercapacitor based on the 0.5 cP/rGO/Co9S8electrode//active carbon exhibits an energy density of¹9.6 Wh kg^–1 at a power density of 400.9W kg^–1.3.MOF structure of Co,Ni bimetallic nanoparticles are prepared by hydrothermal method using terephthalic acid as the organic ligand,and the high specific capacitance of MOF structure NiCo₂O₄ oxide is obtained after annealed in air.A specific capacitance of¹072.0 F g^–1 is achieved for the NiCo₂O₄ nanoparticles at the current density of 1.0 A g^–1.This work has been preliminarily explored the preparation of MOF structure bimetallic compounds using terephthalic acid as the organic ligand and expanded the applications of MOF structure in the field of supercapacitors.