Intercalative pseudocapacitive anhydrous NiC2O4 quantum dot electrode for the fabrication of supercapacitor using aqueous KOH and neutral Na2SO4 electrolyte

Abstract

The energy storage capacity of a material depends on the active-ion arrangement and electron transfer rate at the electrode−electrolyte interface. Overcoming the low power density issues of batteries, the pseudocapacitive electrode can be an excellent alternative to improve the power density of the full cell in Asymmetric Supercapacitors (ASCs) mode to make grid-scale energy storage and delivery feasible. Quantum dots (QDs) is another class of nanomaterial that exhibits unique optical and electrical properties due to the quantum confinement effect and shows high mobility of diffused ions due to nanoscale dimension resulting in a very high surface area. Anhydrous NiC2O4 QDs are envisaged here as a potential energy storage material partly because of the presence of planer oxalates anions (C2O42−) resulting in a quasi-zero 2d arrangement. Superior specific capacity equivalent to 227.5mAh/g (capacitance:1638 F/g) at 1A/g in the potential window of 0.5 V was observed for Anhydrous NiC2O4 QDs electrodes in an aqueous 2 M KOH electrolyte. The battery-type intercalative pseudocapacitance mechanism seems to operate behind the high charge storage capacity of anhydrous NiC2O4 QDs. Almost 22 % (surface controlled) and 78 % (diffusion-controlled intercalative) storage was observed for anhydrous NiC2O4 QDs electrodes. Further, in a full cell, asymmetric supercapacitors (ASCs) mode in which porous anhydrous NiC2O4 QDs are made as the positive electrode and Activated Carbon (AC) as the negative electrode, operating potential window 1.6 V, the highest specific energy of 292 Wh/kg at a specific power of ~772 W/kg and Even at a high power density of 2884 W/kg− at an energy density equivalence of 87 Wh/kg was obtained with high cyclic stability in aqueous 2 M KOH electrolyte. Even in neutral 1 M aqueous Na2SO4 electrolyte, and in the operating potential window 1.6 V, The highest specific energy of 126 Wh/kg and specific power of ~480 W/kg at 1 A/g current density was observed in 1 M Na2SO4 was obtained with high cyclic stability for NiC2O4 QDs full cell in ASCs mode.