Double-layer nickel-cobalt hydroxide (Ni-Co) (LDH) has been investigated as a promising supercapacitor electrode material. A recent study published in the International Journal of Energy Research focuses on the innovative use of the hybrid of graphene oxide (GO) and single-walled carbon nanotubes (SWCNHs) as an efficient platform for coating materials LDH.
Study: Ni-Co layer double hydroxide coated on graphene oxide microsphere nanocomposite and single-walled carbon nanotubes as supercapacitor electrode material. Image credit: Peter Sobolev/Shutterstock.com
The new supercapacitor electrode material based on Ni-Co LDH and GO/SWCNH composite is a potential choice for pseudocapacitor applications due to its superior electrochemical properties and ease of production, ideal for various commercial applications and industrial
Why are supercapacitors so important?
Clean and renewable energy technologies are currently being explored to address the global challenges of energy consumption and sustainability. As a result, competition for more efficient energy storage systems, such as supercapacitors and regenerative batteries, has increased dramatically.
Supercapacitors have attracted much interest in scientific communities due to their high energy density, fast charge/discharge rates, and extended cycling stability. Supercapacitors are classified as electric double layer capacitors (EDLCs) or pseudocapacitors, depending on their energy storage mechanism.
Energy storage in an EDLC is related to a non-Faradaic mechanism involving physical absorption and dissociation of electroactive species on the surfaces of the supercapacitor electrode material and electrolytes. On the other hand, energy storage in pseudocapacitors mainly depends on the reversible Faradaic interactions between the interface functional groups of the supercapacitor electrode material.
Supercapacitor electrode material: overview and challenges
Graphene oxide (GO) has attractive properties for supercapacitor electrode material applications, such as numerous reactive groups and multimodal ion transport pathways. However, the graphene oxide-based supercapacitor electrode material also has significant drawbacks, such as the discharge of graphene layers during the reduction reaction, insulating properties, and low bulk density.
SWCNHs have also been investigated as a supercapacitor electrode material due to their large specific surface area (SSA), tunable porous structure, and excellent electrical conductance. SWCNHs with conical tubular structures form robust spherical aggregates and have single-walled closed graphitic structures comparable to single-walled carbon nanotubes (SWCNTs).
However, unlike SWCNTs with exceptional crystallinity, SWCNHs contain several structural defects such as pentagons and heptagons, which allows nanoscale holes to develop at the interface of SWCNHs in oxidizing environments, restricting their usability as electrodes for suitable supercapacitors.
Ni-Co layered double hydroxide as a supercapacitor electrode material
Electrode substances such as metal oxides, metal hydroxides, and conducting polymers are considered extremely ideal contenders for pseudocapacitive energy storage technologies due to bidirectional Faradaic processes at electrode-electrolyte contacts.
Nickel-cobalt (Ni-Co) double-layer hydroxide (LDH) with tunable topologies is an attractive supercapacitor electrode material due to its cheap cost, non-toxicity, abundance in nature, and exceptional electrochemical stability.
Hydrothermal and electrolytic deposition techniques generally create Ni-Co nanostructures. Structural morphologies significantly affect the electrolytic capacities of Ni-Co layered double hydroxide electrodes. Therefore, the composites of Ni-Co nanostructures and porous carbon substances such as graphene oxide (GO) and SWCNHs need to be investigated to increase the efficiency of Ni-Co LDH-based supercapacitor electrode material.
Current research highlights
In this study, the researchers developed a two-step technique to produce composite materials composed of Ni-Co LDH, graphene oxide (GO), and oxidized single-walled carbon nanotubes (SWCNHs). The initial step was to spray-dry a combination of GO and SWCNH to create spherical hybrid particles ideal for mass manufacturing due to the simple and cost-effective procedure.
In the second step, extremely thin nickel-cobalt (Ni-Co) LDH nanosheets were hydrothermally coated with graphene oxide microspheres and single-walled carbon nanotubes to fabricate the new supercapacitor electrode material.
The pseudocapacitive activity of the hybrid supercapacitor electrode material was evaluated in specific capacitance and cycle efficiency. During the study, the impacts of the composition of the activated carbon substrate on the morphology and electrolytic efficiency of the Ni-Co LDH were also investigated.
Important results of the study
The composite based on graphene oxide and SWCNHs had relatively high electrical conductance and SSA, resulting in a significant effective area for interactions between the supercapacitor electrode material and electrolyte ions during the electrolysis reaction.
The new supercapacitor electrode material based on Ni-Co LDH and GO/SWCNH composite demonstrated considerably high gravimetric specific capacitance and outstanding specific capacitance stability in an aqueous electrolyte environment. These outstanding findings could be attributed to the high electrical conductance and pseudo-capacitance of GO/SWCHN and Ni-Co coated LDH nanohybrids.
Based on these results, it is reasonable to state that the new supercapacitor electrode material developed in this work has significant potential for future energy storage applications.
reference
Kim, JH et al. (2022). Ni-Co layered double hydroxide nanocomposite coated graphene oxide microsphere and single-walled carbon nanohorns as supercapacitor electrode material. International Journal of Energy Research. Available at: https://onlinelibrary.wiley.com/doi/10.1002/er.8657
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