Materials developed from metal-organic frameworks (MOFs) have been researched as enhanced energy-storing components in high-energy application areas. In a study published in the journal Materials Letters, graphene/NiCo2O4 nanosheets were prepared and integrated into supercapacitor applications as an electrode material to improve performance demonstrating high capacity and electrochemical abilities.
Study: 2D/2D nanostructures based on NiCo2O4/graphene composite for high-performance battery-type supercapacitor. Image Credit: Illus_man/Shutterstock.com
The Outstanding Potential of Supercapacitors
In comparison with conventional electrolyte capacitors, a supercapacitor is capable of storing high quantities of energy. It is preferred over battery packs due to its faster and easier recharging and quicker charge transmission.
Due to their minimal resistance, supercapacitors have the capability of producing tremendous power and thus allow for large current loads. The charging technique is straightforward and quick, and there is no risk of overcharging. A supercapacitor offers superior low- and high-temperature charging and discharging capability compared to batteries. Supercapacitors are also quite dependable and have a low impedance.
Due to their large power and acceptable energy densities, quick charging/discharging capabilities, and extended cyclic life, supercapacitors have an important part to play in electronic systems.
Strengths and Weaknesses of Metal Organic Frameworks
Owing to their low cost, large stored specific capacitance (Cs), and excellent charging/discharging characteristics, transition metal oxides (TMOs), particularly spinel nickel-cobalt oxide (NiCo2O4), have received a lot of attention as pseudo-capacitors. The charge storing capabilities of these TMOs are unfortunately also affected by their porosity and morphological structures.
Metal-organic frameworks (MOFs) offer several important qualities, including extensive surface areas, variable makeup, various architectural morphologies, and the ability to function as a sacrificial framework. Particularly, ZIF-67 and ZIF-8 have been extensively studied to manufacture a nanostructure with high porosity and homogeneous architecture.
The chemical and thermal stability of these MOF-derived substances, however, was low, leading to suboptimal electrolytic performance. As a result, combining MOF-derived materials with various supportive matrixes, like CNTs and graphene, has been heavily focused on improving electrolytic activity.
Developing 2D/2D Nanostructures for Highly Effective Supercapacitors
The cutting-edge super-capacitive electrode built on spinel nickel-cobalt oxide nanowires (NWs) coupled with three-dimensional graphene aerogel electrode has achieved a significant Cs with an 84 percent retention for 1000 cycles.
One previous research described a hollow graphene/ NiCo2O4 composite electrode with an extremely high specific capacitance. Furthermore, the three-dimensional free-standing foam electrode of NiCo2O4@graphene preserved 95 percent of its original specific capacitance after even 5000 cycles.
Another research described a flower-shaped composite electrode of nickel-cobalt oxide and multi-walled carbon nanotubes with a good specific capacitance and 75 percent retention after 3000 cycles. In this study, the researchers used a composite of ZIF-67 and graphene oxide (GO) framework-based NiCo2O4 nanofilms and graphene nanofilms (2D/2D nanoscale structure) for a high-performing supercapacitor.
Incorporating graphene can offer superior physical stability and a large contact area for electrolytic ion movement and boost NiCo2O4's rapid electron transference property. As a result of the synergetic impact among the conducting nanofilms of graphene and the redox-active NiCo2O4 nanofilms, improved electrolytic activity may be achieved.
Highlights of the Study
Cyclic voltammetric (CV) and Galvanostatic charging/discharging (GCD) analyses were conducted in 1M potassium hydroxide electrolyte at ambient conditions to assess the electrolytic behavior of the NiCo2O4/G HNSs and the NiCo2O4 electrodes.
Altogether, the findings showed that coupling hetero-nanofilm architectures, one of which is metallic oxide nanofilms. At the same time, the other is graphene-based nanofilms, which may prove to be a preferable framework for creating high-power, long-lasting energy storing systems.
The NiCo2O4 nanofilms were found to have a homogeneous distribution of electron transference as well as mechanical support, leading to superior electrolytic behavior.
The ZIF-67 and graphene oxide templates yielded high porosity, active redox products, including NiCo2O4 nanofilms. By eliminating the templates during the calcination process, the oxygen functionality on the graphene oxide surface enabled homogenous integration of bimetallic NiCo-MOFs precursors to create high porosity two-dimensional NiCo2O4 nanofilms.
The electrolytic behavior of the created 2D/2D NiCo2O4/G HNSs electrode outperformed the raw NiCo2O4. The developed electrode demonstrated long-term robustness due to graphene's excellent mechanical support and electrical conductance.
The suggested 2D/2D composite electrode architecture might be employed as battery-type electrode material in developing energy storing technologies as elastic asymmetrical supercapacitors and as electrodes in lithium-ion capacitors/batteries.
Venkatesh, K., Karuppiah, C., Palani, R., Periyasamy, G., Ramaraj, S. K., & Yang, C.-C. (2022). 2D/2D nanostructures based on NiCo2O4/graphene composite for high-performance battery-type supercapacitor. Materials Letters. Available at: https://doi.org/10.1016/j.matlet.2022.132609