Carbon dots impregnation in cobalt-zinc-nickel metal hydroxyl carbonate: a strategy to mend energy storage

For meeting the continuously increasing demand of portable electronics and green transportation there is a need of supercapacitors with high energy densities without sacrificing its power density and cycling stability. One of the most promising electrode materials for supercapacitor application is transition metal hydroxyl carbonates, since have multiple oxidation states shows enhanced energy storage. Herein, a simple, binder free approach has been used to synthesize metal hydroxyl carbonate (MHC). Changes in valence states in transition metals leads to phase transformation because of which sluggish bulk phase reaction and dramatic volumetric expansion or shrinkage occurs during energy storing process. All this ultimately leads to low electrochemical reaction kinetics and inferior cycling stability. To overcome such disadvantages highly conductive carbon such as carbon dots (CDs) (OD carbon) which have beneficial attributes of low cost, eco-friendliness, high stability and electron mobility and a greater number of functional groups such as amino, hydroxyl, carbonyl, etc., are incorporated into MHC. CD incorporation leads to enhanced properties of MHC such as specific surface area, conductivity, specific capacitance, etc. Green and economical approach was employed to conquer the properties of CDs for high energy density electrode materials. CDs incorporation into MHC, highly improved the electrochemical performance of the electrode material as compared to only MHC because of favorable electronic and surface properties of CD. CDMHC exhibit a superior specific capacity of 2180 C g^-1 at a current density of 5 A g^-1 and excellent cycling stability. CD and MHC combination could pave the way for an excellent electrode tactics for high- performance supercapacitors. (author)