| Supercapacitors, as a desirable energy storage device between traditionally static capacitorsand secondary batteries, have drawn extensive research and more attention recently, due to theirhigh power density, long cycle life and reliable safety. Particularly, Co3O4, thanks to their hightheoretical specific capacitance (SC), low cost, environmentally benign nature and goodelectrochemical reversibility, has been considered as one promising electrode material for next-generation high-performance supercapacitors. However, the traditional preparation technologyof pellet electrode has greatly decreased the porosity and electroactive surface area ofelectrode，which not only makes electrode difficultly wetted by electrolyte, but hinders iontransportation. Additionally, the use of the organic binder also increases the electrode resistance,resulting in low specific capacitances and poor cycle life at high rate for Co3O4with inherentpoor electronic conductivity. Based on above considerations，In this thesis，we mainly focuson the design and controllable synthesis of self-supported Co3O4electrode material, avoidingthe pelletizing process and the use of organic binder, with the ultimate aim to harvest theintriguing self-supported Co3O4electrode material with convenient ions and electronstransportation, and abundant electroactive sites for efficient energy storage. The detailedresearch contents of the thesis were described as follows:1. We successfully developed a self-supported Co3O4nanoparticles (NPs)/nickel sheetelectrode via a one-step hydrothermal deposition of Co3O4NPs on a nickel sheet substrateon large scale. Of note, the pretreatment of “HNO3-etching” played a significant role inone-step hydrothermal deposition of Co3O4on a nickel sheet. Because of direct growth ofCo3O4NPs on the nickel sheet substrate, the Co3O4NPs had a good electrical contact withthe nickel sheet substrate. In addition, abundantly nanoscale mesopores existed betweenneighboring Co3O4NPs, which made electrolyte ions and electrons fast contact with richelectroactive sites for sufficient faradic redox reaction towards highly efficient energystorage and release. Electrochemical data demonstrated that the self-supported Co3O4NPs/nickel sheet electrode exhibited an high SC of784F/g at12A/g, based on thismaximum value, the SC degradation after another continuous2200cycles was only ca.7%,indicating its excellent power density and desirable electrochemical stability for nextgeneration supercapacitors. 2. A one-step hydrothermal strategy was developed for constructing a light andflexible Co3O4monolayer microsphere arrays/graphene sheets (GNs)-carbon nanotubes(CNTs) composite film as a self-supported electrode, and its formation mechanism waslucubrated. It was demonstrated that the synergetic effect of the precipitant NH3·H2O andoxygen-containing functional groups on the graphene oxide (GO) surface played a key roleon the one-step growth of Co3O4on GNs-CNTs film. The alkaline hydrothermal treatmentleaded to not only the deposition of Co3O4, but also the reduction of the GO sheetsmeanwhile. The flexible Co3O4microsphere arrays/GNs-CNTs composite film achievedconvenient electron transportation between electro-active Co3O4and the conductiveskeleton (GN-CNTs), fast ion diffusion channels and enhanced electroactive area, whichmade Co3O4obtain high electrochemical utilization and good electrochemical stability athigh rate. Electrochemical evaluation revealed that this unique flexible film electrode coulddeliver an SC of378F/g at2A/g, and even297F/g at8A/g. Furthermore, After3000times of continuous cycling at varying current densities, the SC of the electrode waswithout noticeable decrease，indicating their excellent power performance and impressiveelectrochemical stability.3. We proposed a two-step strategy involving electrodeposition of hydroxidesfollowed by a calcination process to construct ultrathin mesoporous Co3O4nanosheetarrays directly grown on the3D porous nickel foam substrate. This unique electrode had ahierarchically porous (macropore and mesopore) structure and large specific surface area.Furthermore, it achieved the direct contact of each nanosheet to the underneath conductiveNi foam and good electron contact, which were undoubtedly convenient to the sufficientpenetration and diffusion of the electrolyte in the whole electrode. Furthermore, as long asthe depth of diffusion was increased, more electroactive sites would be obtained, whicheffectively increased the electrochemical utilization of electroactive material.Electrochemical data revealed that an SC of the self-supported ultrathin mesoporous Co3O4nanosheet arrays/nickel foam was delivered as high as2735F/g (ca.3.8F/cm2) at2A/g,even if the current density got to10A/g, the SC still maintained as1471F/g, indicating itsgood power density property. After3000times of continuous cycling at varying currentdensities, the mass SC of the electrode hardly decayed, exhibiting its excellentelectrochemical stability．... |
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