Simple fabrication of (CoFe)Se2 @NC electrode materials derived from MOF materials and the electrochemical properties for supercapacitor

Abstract

Porous carbon nanocomposites and transition metal selenides generated from metal-organic frameworks (MOF) are suitable electrode materials for electrochemical energy storage applications owing to their substantial open space, but their preparation is still fraught with difficulties. Herein, we prepared CoFe Prussian blue-like (CoFe-PBA) nanocubes by a simple co-deposition method and obtained CoFe-PBA@PPy by polymerically assembling CoFe-PBA coated with polypyrrole (PPy), and then successfully prepared (CoFe)Se2 @NC nanocomposites with nitrogen-doped carbon (NC) coated with (CoFe)Se2 by one-step selenization in nitrogen at 400 °C and their structures and morphologies were investigated in depth. This carefully prepared (CoFe)Se2 @NC nanocomposite with an open skeleton structure contains large enough coordination space gaps, porous conduction networks, and a large number of redox-active sites, so that it can largely enhance the kinetic performance of electron and ion transport and facilitate pseudocapacitive reactions, optimize the cycling stability of energy storage devices, and prolong the lifespan of actual devices. Moreover, a stable structure can be maintained during the cycle process and is less likely to collapse, depending on the flexibility and mechanical qualities of the NC. The active material was fixed in nickel foam by a coating method and dried as the electrode for the supercapacitor, and its electrochemical performance was evaluated. The outcomes demonstrated the specific capacitance of the (CoFe)Se2 @NC electrode material could reach 867 F/g at 1 A/g of current density, and its specific capacitance can still reach 640 F/g at a high current density of 5 A/g. Even after 20000 cycles, it still maintains good cycling stability and 99% specific capacitance retention. In addition, we used a brand-new asymmetric all-solid-state supercapacitor (all-solid-state supercapacitor ASC) with (CoFe)Se2 @NC as the positive electrode, Fe2O3/RGO as the negative electrode, and potassium hydroxide/polyvinyl alcohol (KOH/PVA) gel as the electrolyte. The asymmetric all-solid-state supercapacitor of (CoFe)Se2 @NC//Fe2O3/RGO showed remarkable electrochemical performance with an energy density of up to 20 Wh/kg and a power density of 750 W/kg. The supercapacitor was also found to have good cycling stability in the test, with a capacitance retention of 81.1% after 6500 cycles at a current density of 2 A/g.