Study On Synthesis And Properties Of Cobalt-based MOF Derived Supercapacitor Materials

The supercapacitors,the new type of electrochemical device,have excellent power density but insufficient energy density.In recent years,pseudocapacitors with high specific capacity have received widespread attention.Transition metal compounds have been used as common electrode materials for pseudocapacitors,including cobalt-based oxide with high specific capacity.In this paper,MOF-derived Zn Co₂O₄(ZCO)and the compound of Zn Co₂O₄and NiCo₂S₄has been prepared as the electrode materials for supercapacitor,and the electrode materials for supercapacitor with good specific capacity,rate performance and cycle retention has been synthesized by adjusting their preparation conditions and modification methods and combining with sulfide materials.The main research contents are as follows:1.Preparation of MOF-derived ZCO/NCS materials by hydrothermal method:Zn Co₂O₄(ZCO)derived from ZIF-8/67 were directly prepared by aqueous solvent method and pyrolysis,which showed a specific capacity of 744 F/g@1 A/g.To improve the electrochemical performance of the materials,chemical etching with tannic acid aqueous solution was used to the ZIF,and the specific capacity of ZCO is significantly improved,in which ZCO-20 sample obtained when etching for 20 minutes showed the highest capacity(1651 F/g@1 A/g).Then,the core-shell structure composites of ZCO and nickel-cobalt sulfide(NCS)were prepared by one-step hydrothermal method,among which the ZCONCS-20 sample exhibited excellent specific capacity(2084F/g@1 A/g)and rate performance(1215 F/g@10 A/g).2.Preparation of MOF-derived ZCO/NCS materials by electrochemical deposition method:MOF-derived Zn Co₂O₄with different cubic morphologies(ZCOC)were prepared by the solvothermal method with organic solvent and pyrolysis.After etching by tannin aqueous solution etching for 20 minutes,the obtained ZCOC-20 sample showed the best electrochemical properties(1687 F/g@1 A/g).After that,the composite materials of ZCOC and NiCo₂S₄(ZCOCNCS)were prepared by electrochemical deposition method,and the process parameters for electrochemical deposition were analyzed.ZCOCNCS-20 prepared at-0.9V for 10min exhibited excellent specific capacity(2385 F/g@1 A/g)and rate performance(990 F/g@50 A/g).3.Preparation and property analysis of asymmetric supercapacitor devices:The prepared ZCOCNCS-20 materials were assembled into an asymmetric supercapacitor device with activated carbon as negative electrode materials and PVA/KOH gel electrolyte,and the electrochemical properties of this device were tested.This device showed an excellent specific capacity(161 F/g@1 A/g),and the highest energy density and power density reached 57.28 Wh/kg and 8000 W/kg.This device was also tested by charge-discharge cycles at a current density of 10 A/g,and its capacity retention after5000 cycles was 91.5%,which showed good property of cycling at high rate.