Copper-nickel rubeanate metal-organic framework, a new highly stable and long active life nanocomposite for high-performance supercapacitors

High-performance supercapacitors require electrodes featuring a high surface area,suitable porosity,and conductivity.Metal-organic frameworks(MOFs)hold a high surface area and suitable porosity while insufficient conductivity.Herein,a single-step chemical strategy was developed to directly synthesize a composite of copper-nickel rubeanate MOF and highly conductive reduced graphene oxide(rGO)nanosheets(CNRG-MOF)on nickel foam(CNRG-MOF/NF)electrode.The nanocomposite enables it to use as a high-performance supercapacitor electrode.The bimetallic CNRG-MOF/NF electrode exhibits su-perior electrochemical performance than its single metallic counterparts.The optimized CNRG-MOF/NF electrode represents a high specific capacitance of 846.15 F g1 at a current density of 1.0 A g1.A three-electrode system exhibited up to 96.37%capacitance retention after 7000 galvanostatic charge-discharge(GCD)cycles,indicating its excellent stability.These results may pave the way for the direct use of MOF materials for electrochemical energy devices instead of pyrolyzing the MOFs to improve the conductivity while losing controllable structural merits.GCD curve was obtained at different current densities to evaluate the nanocomposite's asymmetric setup charge storage capability.The electrode capacity for the asymmetric system was measured as 93.3 F g1,which proves the capacitive property of CNRG-MOF/NF electrode.

Stabilities of Flexible Electrochemical Capacitors Based on Polypyrrole/Carbon Fibers in Different Gel Electrolytes

Flexible electrochemical capacitors（ECs） are vitally important as the emerging flexible electronics.We have prepared polypyrrole doped with counter ion of Cl-on carbon fibers（PPy-Cl/CFs） via the simple electrochemical deposition method.The flexible ECs based on PPy-Cl/CFs electrodes have been assembled by using H_3PO_4/poly（vinyl alcohol）（PVA）,H_2SO_4/PVA,LiClO_4/PVA,KCl/PVA and Li Cl/PVA as gel electrolytes.The capacitive properties of ECs have been systematically evaluated with electrochemical methods.The results show that the cells with H_3PO_4/PVA electrolyte exhibit good cyclic stability（91.5% retention after 15000 cycles） although PPy-Cl/CFs has moderate specific capacitance in H_3PO_4/PVA（41.6 m F·cm^-1 or 52.0 F·cm^-3）.However,the ECs in other electrolytes have poor cyclic stability.Further electrochemical analysis reveals that the doping/dedoping processes of PPy-Cl/CFs are different in the five electrolytes,and X-ray photoelectron spectra demonstrate that the ratios of counter anions in PPy＇s oxidized states to those in reduced states are obviously different when PPy-Cl/CFs are kept in reduced or oxidized states in the five electrolytes.The results also illustrate why the capacitors using H_3PO_4/PVA as electrolyte exhibit good cyclic stability.Furthermore,a light emitting diode（LED） with a threshold voltage of 2.5 V can be lighted by three ECs connected in series.