Electrochemical Performance Of Mo₂C,MoS₂/PEI-GO Nanomaterials As Negative Electrode Materials For Supercapacitors

The development of advanced energy storage devices is at the forefront of research geared towards a sustainable future.Nanostructured materials are advantageous in offering huge surface to volume ratios,favorable transport features,and attractive physicochemical properties.They have been extensively explored in various fields of energy storage and conversion.This work is focused largely on the nanostructured materials,thus preparing the Mo₂C and MoS₂/PEI-GO nanomaterial.The microstructure and morphology of these as-prepared materials were analyzed by XRD,SEM,TEM and XPS methods.At the sametime,the electrochemical performances were evaluated by cyclic voltammetry?CV?,galvanostatic charge-discharge?GCD?,and electrochemical impedance spectra?EIS?.Then,the relation between the electrochemical performance and structure was studied.The main research details and results are as follows:?1?Molybdenum carbide?Mo₂C?presents high capacity due to their excellent conductivity as well as faradic reactions with protons on the surface.Molybdenum carbide nanoflakes have been synthesized by calcining amine metal oxide and been served as a capacitive material for supercapacitors.Proton ionic liquids,a class of novel electrolyte,can provide protons for electrochemical reactions and expand the operating potential window and therefore guaranteeing the high energy density.A specific capacitance of 88 F g^-1 is achieved in 2 mol L^-1 1-ethyl-3-methylimidazolium acetate/acetonitrile?EMIMAc/AN?electrolyte at a current density of 0.5 A g^-1.The assembled asymmetric Mo₂C//AC capacitor with an operating voltage of 2.5 V exhibits a good cycling performance?maintained 95.6%after 1200cycles?and a high energy density of 44.1 W h kg^-1.The prominent capacitive performance could be attributed to rapid electron transfer and highly exposed active sites of Mo₂C nanoflakes.Besides,1-ethyl-3-methylimidazolium acetate ionic liquid provides wider electrochemical window to ensure large output.?2?The stable water dispersion suspensions of molybdenum disulfide?MoS₂?are prepared by a simple hydrothermal method and then a chemical stripping process.Then,the MoS₂ suspension and the polyethylene amine modified graphite oxide?PEI-GO?are assembled by electrostatic interaction of a negatively charged suspension and a positively charged PEI-GO dispersion to obtain the MoS₂/PEI-GO composites.The mass ratio between MoS₂ and PEI-GO is 8:1.For comparison,the high concentrations of MoS₂?HCMoS₂/PEI-GO?and the high concentrations of GO?MoS₂/HCPEI-GO?were also prepared.However,two of them almost had the same specific capacitance as the MoS₂/PEI-GO,suggesting that the negatively charged exfoliated-MoS₂ were strongly adsorbed on positively charged PEI-GO nanosheets through electrostatic interaction until adsorption capacity reached saturation.Meanwhile,MoS₂/GO was synthesized through physical mixing method.The specific capacitance of MoS₂/GO was much smaller than that of MoS₂/PEI-GO,which indicated that the MoS₂ sheets were tightly anchored on GO sheets through electrostatic interaction,thus exhibiting a superior electrochemical performance.The GO nanosheets not only improved the electronic conductivity of the MoS₂/PEI-GO composites and contributed to an excellent charge transfer network but also hampered the restacking of MoS₂ nanosheets,resulting in the fast electrolyte diffusion.The composites achieve the highest specific capacitance of 153.9 F g^-1 where 83.5%of the initial specific capacitance still remains after 5,000 cycles.The asymmetric supercapacitor was assembled:the MoS₂/PEI-GO served as negative electrode,the AC served as positive electrode.The asymmetric supercapacitor provided a maximum capacitance of 42.9 F g^-1,and 95%of the initial capacitance was maintained after 5,000 cycles.Furthermore,a MoS₂/PEI-GO//AC asymmetric supercapacitor delivered an energy density of 19.3 Wh kg^-1 and a power density of 4500 W kg^-1,indicating the potential of the hybrid MoS₂/PEI-GO composites in electrochemical energy-storage applications.