Supercapacitive Performance Of Co Prussian Blue Analogues Synthesized By Sacrificial Template Method

With increasing social awareness of environmental problem,sustainable,reliable,efficient and competitive energy sources have become more and more important.As the intermediate devices between dielectric capacitors and conventional batteries,supercapacitors have attracted significant attention due to their merits,such as superior reversibility,fast charging/discharging,long cycle life and high power density,etc.The rational design and synthesis of nanostructured electrode materials is essential for developing high-performance supercapacitors.In this thesis,nanostructured Co Prussian Blue Analogue（Co PBA）and its composites were studied as electrode materials because of their unique structure and redox properties.Co PBA were synthesized by the sacrificial template method,and the structure and morphology of the prepared materials were characterized by X-ray diffraction（XRD）,scanning electron microscopy（SEM）,transmission electron microscopy（TEM）and Raman diffraction（Raman）.Besides,Cyclic voltammetry（CV）,constant current charge discharge（GCD）and electrochemical impedance spectroscopy（EIS）were tested in 0.5 M Na₂SO₄electrolyte to investigate the electrochemical performance of the sample.Hollow Co Prussian blue analogues/multi-walled carbon nanotubes（Co PBA/MWCNT）composites were synthesized by the sacrificial template method using ZIF-67 as precursor.TEM images revealed that MWCNT wrapped on the surface of Co PBA nanocubes and the C≡N band of Co PBA and G band of MWCNT were detected by Raman.CV curves showed that Co PBA exhibited one pair of the redox peaks(Fe²⁺/Fe³⁺).Whereas,the Co PBA/MWCNT composite electrode exhibited two pairs of the redox peaks(Fe²⁺/Fe³⁺,Co²⁺/Co³⁺).The activation of Co²⁺/Co³⁺redox peak significantly improved the specific capacitance of the material.A specific capacitance of 353 F·g^-1 was achieved under the current density of 1 A·g^-1,34.3%higher than that of pure Co PBA.When the current density increases to 10 A·g^-1,the specific capacitance can still be maintained at 315 F·g^-1.In addition,it was known that Co PBA/MWCNT electrode material was pseudocapacitance material through the calculation of reaction kinetics.Finally,a hybrid supercapacitor Co PBA/MWCNT||AC was assembled by using Co PBA/MWCNT material as the positive electrode and activated carbon（AC）as the negative electrode.The device can be operated at a high cell voltage of 2.0 V.A high energy density of 40.4 Wh·kg^-1 was delivered at a power density of 193.6 W·kg^-1.The capacity retention was 83.1%after 5000 cycles under the GCD of 1 A·g^-1,indicating the excellent cycle stability.Besides,the metal ions-doped Co PBA electrode materials were synthesized by sacrificial template method.Mn-Co PBA,which were derived from the Mn-doped ZIF-67 as precursor,showed enhanced electrochemical performance.SEM images showed that Mn-Co PBA was a polyhedron with rough surface.In 0.5 M Na₂SO₄ electrolyte,the Mn-Co PBA electrode exhibited specific capacitances of 369 and 270 F·g^-1 at the current density of 1 and 5 A·g^-1,respectively.And the capacity retention was 94%after 2000 cycles.