Synthesis Of Cobalt-based Metal Oxides And The Investigation Of Their Pseudocapacitive Performance

Supercapacitor is a new type energy storage device with high power density,excellent cycling stability and fast charge/discharge ability, which have huge potentialapplication in many areas such as hybrid electric vehicles, industrial power, militarydevices and memory backup systems. However, relative low energy density largelylimited its application. In general, rational design and preparation of electrodematerials with excellent electrochemical performance is the key to solve above issues.Metal oxides, for its relatively higher specific capacitance than carbon based materialsand relatively higher stability than polymers based materials, recently attractedtremendous attention and have become a very promising supercapacitor materials. Inthis paper, we design and controlled synthesis of cobalt based metal oxides materialsand composite materials with novel nanoarchitectures and investigation of theirpseudo-capacitive performance.(1) For the first time, we designed an accessible two-step method to synthesizemesoporous ZnCo2O4nanosheet arrays on the surface of highly conductive Ni foamwith strong adhesion and then used it as an integrated electrode for supercapacitorsdirectly. Typically, the first step was the growth of Zn-Co precursor nanosheets on thesurface of Ni foam via a mild hydrothermal reaction; the second step was to convertthe Zn-Co precursor into ZnCo2O4nanosheets via calcination at a relatively lowtemperature. Due to the unique nanostructures, the as-prepared ZnCo2O4nanosheet arrays/Ni foam electrode had a remarkably electrochemical performance withultrahigh specific pseudo-capacitance (2468F g-1at5A g-1) and good cycling stability(only3.7%loss after1500cycles at30A g-1).(2) We successful growth of two types of NiCo2O4nanosheets with different sizesand morphologies on nickel foam substrate via facile hydrothermal method andinvestigation of their electrochemical performance. In the experiment we found thatwhen we used a mixed solution composed of methanol and distilled water as solvent,we obtained bent porous nanosheets with uniform size (1-2μm) and ultrathinthickness (about10nm). These nanosheets were interconnected with each other andthen formed three dimensional nanosheet arrays; while when we used a mixedsolution of glycol and distilled water as solvent, we obtained highly bent porousnanosheets with many wrinkles, their size and thickness were0.5-3μm and10nm，respectively. Like the former, the later nanosheet possessed three dimensionalnanosheet arrays nanoarchitecture. Electrochemical tests illustrated that both the twonanosheet arrays exhibited excellent high specific capacitance and high cyclingstability.(3) NiCo2O4@MnO2core-shell nanosheet arrays hybrid composite material wassuccessful synthesized via a two-step hydrothermal method, which uniformly grownon nickel foam and directly served as integrated electrode for supercapacitors. XRD,EDS, SEM and TEM tests confirmed its composition and morphologies. For thishybrid “core-shell” nanostructure, the “core”，NiCo2O4nanosheets with thickness of10nm, was grown on the Ni foam via the first-step hydrothermal method first, thenthe “shell”, MnO2nanosheets with thickness of2nm, was grown on the “core” ofNiCo2O4nanosheet, formed three dimensional hybrid nanoarchitecture.Electrochemical tests indicated that the NiCo2O4@MnO2core-shell nanosheet arrayshybrid composite exhibited higher capacitance and stability than pure NiCo2O4nanosheet arrays, which demonstrated that grown MnO2nanosheet on NiCo2O4nanosheet undoubtedly enhanced the capacitive performance and cycling stability ofelectrode materials.