Supersonically sprayed self-aligned rGO nanosheets and ZnO/ZnMn2O4 nanowires for high-energy and high-power-density supercapacitors

Abstract

Core-shell-type bimetallic oxide and carbon composites comprising zinc oxide (ZnO) nanospheres and zinc manganese oxide (ZnMn2O4) nanowires were produced by a hydrothermal method, and supersoni-cally sprayed together with reduced graphene oxide (rGO) nanosheets onto Ni foil to fabricate flexible su-percapacitors. The supersonic impact facilitated the exfoliation of the rGO nanosheets, thereby increasing the surface area and adhesion of the composite particles to the substrate. The rGO nanosheets were verti-cally aligned during the supersonic impact and formed localized zones, enabling optimal accommodation of the ZnO/ZnMn2O4 particles. This localization, with the addition of rGO, reduced the agglomeration of ZnO/ZnMn2O4 particles. The molar concentration of MnSO4 used in the synthesis of ZnO/ZnMn2O4 was varied from 0.05 to 0.15 mol/L to determine the optimal MnSO4 concentration that would result in the highest energy storage capacitance. The unique nanostructure of ZnO/ZnMn2O4 and the self-alignment of rGO sheets facilitated a favorable environment for high energy storage capability with a specific capaci-tance of 276.3 mF center dot cm -2 at a current density of 0.5 mA center dot cm-2 and an energy density of 98.2 mu Wh center dot cm-2 at a power density of 1600 mu W center dot cm -2. The width of the potential window was increased to 1.2 V, imply-ing a significant increase in the energy storage capability of the supercapacitor. Capacitance retention of 88% was achieved after 10,0 0 0 charge/discharge cycles for the supercapacitor fabricated using an optimal MnSO4 concentration (0.10 mol/L) during the composite synthesis.(c) 2022 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.