Carbon nanosheets/MnO2/NiCo2O4 ternary composite for supercapacitor electrodes

Abstract

Potassium citrate has been reported to fabricate carbon nanosheets (CNS) through high-temperature calcinations. To integrate electrical double-layer capacitive CNS with high-pseudocapacitive metal oxides, a novel CNS/MnO2/NiCo2O4 ternary composite is developed by growing NiCo2O4 nanoneedles on porous CNS/MnO2 nanosheets arrays, in which, the CNS/MnO2 template was prepared by the redox reaction between CNS and KMnO4. Through optimizing the dosage of CNS/MnO2 template, the CNS/MnO2/NiCo2O4–0.1 composite prepared with 0.1 g CNS/MnO2 presents the highest capacitance of 1254 F g−1, and the capacitance retains 81.9% after cycled for 5000 cycles. The asymmetric supercapacitor device consisted of CNS/MnO2/NiCo2O4–0.1 positive electrode and CNS/CNTs negative electrode delivers a capacitance of 161 F g−1 at 0.5 A g−1. The energy density reaches the maximum value of 22.2 Wh kg−1 at 727.9 W kg−1. The superior performance of the proposed ternary composite can be ascribed to the high conductivity of CNS and the improved ion/charge transfer by porous MnO2 nanosheets arrays. Furthermore, the combination of NiCo2O4 nanoneedles with MnO2 nanosheets contributes to much more pseudocapacitance by playing a synergistic effect.