Graphene‐Based Nanocomposites for Supercapacitors

Abstract

IntroductionSupercapacitors, also called ultracapacitors, as potential electrochemical energy storage devices are applied in a variety of military and commercial applications because of their long cycling lifetime, low maintenance cost, and extraordinarily high power density [1, 2]. A hybrid system combining lithium-ion batteries and supercapacitors has also been attracting the attention of researchers. Supercapacitors can be primary energy devices for power assist during acceleration and hill climbing, as well as for recovery of braking energy. Lithium-ion batteries can provide the energy during cruising. The hybrid system combines the power performance of supercapacitors with the greater energy storage capability of lithium-ion batteries. The hybrid system can also extend the life, downsize the volume, and reduce the cost of batteries.There are two types of supercapacitors (SCs): electric double-layer capacitors (EDLCs) and pseudocapacitors. EDLCs are non-faradaic supercapacitors which store energy using the adsorption of both anions and cations [3,4]. Currently, most of state-of-the-art EDLCs devices are based on high-surface-area carbon [5][6][7][8][9][10][11], such as porous activated carbon (AC). A main issue with AC-based SC electrodes is that the entire surface area is not electrochemically accessible by the electrolyte because of their small micropore size (pore size <2 nm) and hydrophobic graphene-like surface [12,13]. Therefore, carbon has a low surface-area-normalized specific capacitance of 10-40 μF cm −1 [2, 14] The commercial SC based on AC and organic electrolyte has only an energy density of ∼7 Wh kg −1 [15], although its power density can be as high as 10 kW kg −1 as shown in Figure 4.1. Therefore, it is essential to develop novel electrode materials with large accessible specific surface area (SSA) and better electrolyte affinity, contributing to a higher energy density.Unlike EDLCs which store energy through physical adsorption, pseudocapacitive materials [17] store energy through a faradaic process, which involves fast and reversible redox reactions between the electrolyte and electroactive materials on the electrode surface [18]. In principle, the electroactive species, which possess Graphene-based Energy Devices, First Edition. Edited by A. Rashid bin Mohd Yusoff.

Self-Assembled Hierarchical Silkworm-Type Bimetallic Sulfide (NiMo3S4) Nanostructures Developed on S-g-C3N4 Sheets: Promising Electrode Material for Supercapacitors

“…Basically, g-C 3 N 4 is different from traditional carbon materials with a two-dimensional (2D) nanosheet structure, which is an ideal conductive platform to accommodate nanobulbs of active materials in the electrochemical process and facilitating active material to fill the void spaces, simultaneously enhancing the conducting channels for electron transportation. Interestingly, g-C 3 N 4 nanosheets are flexible to induce various types of surface structures of noble metal composites, which further depends on synthesis parameters. − The hierarchical self-assembled silkworm-like morphology of NiMo 3 S 4 on S-g-C 3 N 4 is evidenced in Figure d–f. The SEM images of the NMS@S-gC nanocomposite clearly show the formation of small nanobulbs that are formed as silk-warm type structures and those were wrapped on the surface of S-gC porous nanosheets.…”

Graphene Nanocomposite Materials for Supercapacitor Electrodes

“…Further examples of composites of graphene and its relatives with metal chalcogenides can be found in overviews and selective reviews [48,[107][108][109][110][111][112][113][114]. Particular attention to preparation and fabrication processes has been paid in [115].…”