3D Hierarchical structure Electrodes of MnO₂ Nanosheets Decorated on Needle‐like NiCo₂O₄ Nanocones on Ni Foam as a cathode material for Asymmetric Supercapacitors

Abstract

In this work, three dimensional (3D) hierarchical structure electrode of MnO2 nanosheets decorated on needle‐like NiCo2O4 nanocones hybrid arrays on Ni foam is designed by a two‐step hydrothermal process. In this special structure, 3D hierarchical NiCo2O4/MnO2 core/shell composites have high specific surface area and large pore structure, which makes it easier to reach the active site, and shorten the ion transport path. Used as electrode for supercapacitors, the composites can develop their respective strengths, and the synergies between different components can also improve capacitance and speed capacity. The electrochemical results exhibit that the NiCo2O4/MnO2 core/shell electrodes display a large capacitance of 816 F⋅g−1 at the current density of 5 mA⋅cm−2, and show an excellent cycling stability (81% retention after 5000 cycles). Four Asymmetric supercapacitors (NiCo2O4/MnO2//BPC (banana peel), NiCo2O4/MnO2//BHC (buckwheat husk), NiCo2O4/MnO2//PPC (pomelo peel), and NiCo2O4/MnO2//AC (activated carbon)) using the NiCo2O4/MnO2 core/shell as a positive electrode and biochar as a negative electrode are assembled. The results indicate that all the asymmetric supercapacitors deliver a high operation voltage of 1.6 V, and NiCo2O4/MnO2//BPC exhibits excellent specific capacitance (85.4 F⋅g−1 at the current density of 5 mA⋅cm−2), high energy density (30.4 Wh⋅kg−1 at the power density of 133.5 W⋅kg−1) and remarkable cycling stability (only decrease by 12% after 5000 cycles).

High-Energy Asymmetric Supercapacitor Based on the Nickel Cobalt Oxide (NiCo2O4) Nanostructure Material and Activated Carbon Derived from Cocoa Pods

“…The adopted technique is a classical and perhaps the simplest means to synthesize metal oxide nanoparticles. As a kind of binary-metal oxide, NiCo 2 O 4 has been largely explored and proved to have exhibited improved electrochemical performances compared to the corresponding individual metal oxide resulting from its higher theoretical capacitance and more faradaic redox reactions occurring at the its electrode–electrolyte. ,− The p-type semiconductor material is known for a band gap of 2.1 eV along with an electronic conductivity of nearly a 2-fold order of magnitude higher compared to Ni and Co oxides. The binary-metal oxide material’s morphology, structure, and thermal ability alongside its electrochemical performances were cautiously investigated.…”

Fabrication of Fe3O4-incorporated MnO2nanoflowers as electrodes for enhanced asymmetric supercapacitor performance

“…The results clearly demonstrate that the MnO 2 @Fe 3 O 4 nanoflowers/AC device exhibits a remarkable performance than the previously reported asymmetric supercapacitors. 57–66…”

“…The results clearly demonstrate that the MnO 2 @Fe 3 O 4 nanoflowers/AC device exhibits a remarkable performance than the previously reported asymmetric supercapacitors. [57][58][59][60][61][62][63][64][65][66] To further elucidate the long-term cycling stability of the MnO 2 @Fe 3 O 4 nanoflower/AC device, 5000 GCD cycles were performed consecutively at a constant current density of 15 A g −1 (Fig. 5(f)).…”

NiCo2O4/C Core‐Shell Nanoneedles on Ni Foam for All‐Solid‐State Asymmetric Supercapacitors

“…One approach is to introduce oxygen vacancies, however, the reduced NiCo 2 O 4 is unstable and can be easy to transfer into the previous state . Another strategy is to combine NiCo 2 O 4 and conductive materials (active carbon, graphene and conducting polymers) or directly grow on conductive current collectors (Ni foam, carbon fiber) . Although the capacitance of NiCo 2 O 4 demonstrates a notable improvement by adopting the above methods, its effective utilization is still well below the theoretical value.…”

“…[15] Another strategy is to combine NiCo 2 O 4 and conductive materials (active carbon, graphene and conducting polymers) or directly grow on conductive current collectors (Ni foam, carbon fiber). [8,[16][17][18][19][20][21] Although the capacitance of NiCo 2 O 4 demonstrates a notable improvement by adopting the above methods, its effective utilization is still well below the theoretical value. To address this issue, NiCo 2 O 4 /C composites grown on current collectors have been investigated.…”