Supercapacitor electrodes with graphene oxide and carbon nanohorns

Nickel-cobalt (Ni-Co) layered double hydroxide (LDH) has been studied as a promising electrode material for supercapacitors. A recently published study in the International Journal of Energy Research focuses on the innovative use of hybrid graphene oxide (GO) and single-walled carbon nanohorns (SWCNHs) as an efficient platform for LDH coating materials.

​​​​​​Study: Ni-Co-coated double hydroxide coated on microsphere nanocomposite of graphene oxide and single-walled carbon nanohorns as supercapacitor electrode material. Credit: Peter Sobolev/Shutterstock.com

The novel Ni-Co-LDH and GO/SWCNHs-based composite based supercapacitor electrode material is a potential choice for pseudocapacitor applications due to its superior electrochemical properties and ease of fabrication, which is ideal for various commercial and industrial applications.

Why are supercapacitors so important?

Clean and renewable energy technologies are currently being researched to address the challenges of global 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 a great deal of interest in the scientific community due to their high energy density, fast charge/discharge rates, and extended cyclic 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-Faradic mechanism involving the physical absorption and dissociation of electroactive species at the surfaces of the electrode material and the electrolytes of the supercapacitor. On the other hand, energy storage in pseudocapacitors mainly relies on reversible Faradaic interactions between the interface functional groups of the supercapacitor electrode material.

Electrode material for supercapacitors: overview and challenges

Graphene oxide (GO) has attractive properties for applications as a supercapacitor electrode material, e.g. B. Numerous reactive groups and multimodal ion transport pathways. However, the graphene oxide-based supercapacitor electrode material also has significant disadvantages, such as graphene sheets discharging during the reduction reaction, insulating properties, and poor bulk density.

SWCNHs have also been studied as electrode materials for supercapacitors because of their large specific surface area (SSA), tunable porous structure, and excellent electrical conductivity. SWCNHs with tapered tubular structures form robust spherical aggregates and have closed graphitic single-walled structures comparable to single-walled carbon nanotubes (SWCNTs).

However, unlike SWCNTs with exceptional crystallization, SWCNHs contain various structural defects such as pentagons and heptagons, which allow nanoscale holes to develop at the interface of SWCNHs in oxidizing environments, limiting their utility as viable supercapacitor electrodes.

Ni-Co layered double hydroxide as electrode material for supercapacitors

Electrode substances such as metal oxides, metal hydroxides, and conductive polymers are considered highly ideal candidates for pseudocapacitive energy storage technologies due to the bidirectional Faradaic processes at the electrode-electrolyte contacts.

Nickel-cobalt (Ni-Co) layered double hydroxide (LDH) with tunable topologies is an attractive electrode material for supercapacitors because it is inexpensive, nontoxic, abundant in nature, and has excellent electrochemical stability.

Hydrothermal and electrolytic deposition techniques generally produce Ni-Co nanostructures. The structural morphologies significantly affect the electrolytic capabilities of Ni-Co coated double hydroxide electrodes. Therefore, composites of Ni-Co nanostructures and carbon porous substances such as graphene oxide (GO) and SWCNHs need to be explored to increase the efficiency of Ni-Co-LDH-based supercapacitor electrode material.

Highlights of current research

In this study, researchers developed a two-step technique to fabricate Ni-Co-LDH, graphene oxide (GO), and oxidized single-walled carbon nanohorns (SWCNHs) composite materials. In the initial phase, a combination of GO and SWCNHs was spray dried to produce hybrid spherical particles, which are ideal for mass production because of the simple and inexpensive process.

In the second stage, extremely thin nickel-cobalt (Ni-Co) LDH nanosheets were hydrothermally deposited onto graphene oxide microspheres and single-walled carbon nanohorns to fabricate the novel supercapacitor electrode material.

The pseudocapacitive activity of the hybrid supercapacitor electrode material was evaluated in terms of specific capacitance and cycling efficiency. The effects of the composition of the activated carbon substrate on the morphology and electrolytic effectiveness of Ni-Co-LDH were also investigated during the study.

Key Findings of the Study

The composite based on graphene oxide and SWCNHs had a comparatively high SSA and electrical conductivity, resulting in a significant effective area for interactions between the supercapacitor electrode material and electrolytic ions during the electrolysis reaction.

The new Ni-Co-LDH and GO/SWCNHs composite-based supercapacitor electrode material showed a considerably high gravimetric specific capacitance and excellent specific capacitance stability in an aqueous electrolyte environment. These outstanding results could be attributed to the high electrical conductivity and pseudocapacitance of the nanohybrid GO/SWCHNs and coated Ni-Co-LDH.

Based on these results, it is reasonable to state that the novel supercapacitor electrode material developed in this work has significant potential for future energy storage applications.

Relation

Kim, JH et al. (2022). Layered Ni-Co double hydroxide coated on microsphere nanocomposite of graphene oxide 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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