Graphene Quantum Dots: Novel Properties and Their Applications for Energy Storage Devices

Batteries and supercapacitors are the next-generation alternative energy resources that can fulfil the requirement of energy demand worldwide. In regard to the development of efficient energy storage devices, various materials have been tested as electrode materials. Graphene quantum dots (GQDs), a new class of carbon-based nanomaterial, have driven a great research interest due to their unique fundamental properties. High conductivity, abundant specific surface area, and sufficient solubility, in combination with quantum confinement and edge effect, have made them appropriate for a broad range of applications such as optical, catalysis, energy storage and conversion. This review article will present the latest research on the utilization of GQDs and their composites to modify the electrodes used in energy storage devices. Several major challenges have been discussed and, finally, future perspectives have been provided for the better implementation of GQDs in the energy storage research.

Review of research of nanocomposites based on graphene quantum dots

Graphene quantum dots (GQDs) belong to the vast and versatile family of carbon nanomaterials. Their unique position amongst versatile carbon nanoparticles (NPs) originates from the properties of quantum confinement and edge effects. GQDs are similar to conventional semiconductor QDs due to their tunable band gaps and high photoluminescence activity. However, GQDs have superior characteristics due to their excellent biocompatibility, low toxicity, good water dispersibility, large optical absorptivity, high fluorescence activity and photostability. These properties have generated significant interest in GQDs applications in various fields: nanosensor fabrication, drug delivery, photocatalysis, photovoltaics, and photodynamic therapy. Numerous GQD-based nanocomposites/nanohybrides have been synthesized and/or studied computationally. This review focuses on recent computational studies of various GQD-based nanocomposites/nanohybrides and systems which can be related to them.

Facile synthesis of MnCo2S4 nanosheets as a binder-free electrode material for high performance supercapacitor applications

This paper reported an easy synthesis of MnCo2S4 (MCS) nanosheets by a one-pot solvothermal method for high performance supercapacitor electrode material applications. The obtained MCS nanosheets with an ultrathin thickness...

Do amino acid functionalization stratagems on carbonaceous quantum dots imply multiple applications? A comprehensive review

Amino acids are the noteworthy entity among biological molecules with diverse properties such as zwitterionic and amphoteric. Functionalizing carbon-based quantum dots using amino acids might be used for the extreme enhancement of electronic and optical properties of quantum dots and improve the performance of the resultant amino acid-functionalized quantum dots. The amino acid-functionalized quantum dots are highly soluble, sustainable, and biocompatible with virtuous optical and electrical performance, which makes them potential and suitable candidates for fabricating optoelectronic devices. The tenacity of using amino acids as functional groups to functionalize quantum dots and their novel properties are conferred to attain their multiple applications. The goal of this review is to provide the choices of amino acids based on the desired applications and a variety of functionalization techniques to make them a noteworthy material for future applications. The method of one-step and two-step functionalization strategies along with the properties of the resultant functionalized quantum dots and their plausible applications and future scope of the material are highlighted. Amidation is the basic principle behind the functionalization of quantum dots with amino acids. This review would be an exciting prospect to explore the pathways of the possible applications in different domains, in which the amino acid-functionalized quantum dots have not yet been explored. Further, this review article helps in pitching a variety of prominent applications right from sensors to energy storage systems either using the optical property or electronic property of amino acid-functionalized quantum dots.

Shedding Light on Graphene Quantum Dots: Key Synthetic Strategies, Characterization Tools, and Cutting-Edge Applications

During the last 20 years, the scientific community has shown growing interest towards carbonaceous nanomaterials due to their appealing mechanical, thermal, and optical features, depending on the specific nanoforms. Among these, graphene quantum dots (GQDs) recently emerged as one of the most promising nanomaterials due to their outstanding electrical properties, chemical stability, and intense and tunable photoluminescence, as it is witnessed by a booming number of reported applications, ranging from the biological field to the photovoltaic market. To date, a plethora of synthetic protocols have been investigated to modulate the portfolio of features that GQDs possess and to facilitate the use of these materials for target applications. Considering the number of publications and the rapid evolution of this flourishing field of research, this review aims at providing a broad overview of the most widely established synthetic protocols and offering a detailed review of some specific applications that are attracting researchers’ interest.

Hierarchical NiCo2S4@NiCoP core-shell nanocolumn arrays on nickel foam as a binder-free supercapacitor electrode with enhanced electrochemical performance

A novel hierarchical core-shell nanocolumn array, with NiCo₂S₄ hollow nanowire (NiCo₂S₄ H-NW) as the core and NiCoP nanosheet (NiCoP NS) as the shell, has been directly synthesized on nickel foam (NF) as self-supported, binder-free electrode for high-performance supercapacitors. The morphological characterizations reveal that the diameter of NiCo₂S₄ H-NW core is ∼100 nm and the diameter of single NiCo₂S₄@NiCoP core-shell nanocolumn is ∼250 nm. Through a series of electrochemical tests and the analysis of charge storage kinetics, hierarchical NiCo₂S₄@NiCoP/NF electrode presents high areal specific capacitance of 5.98 F/cm² at 1 mA/cm², outstanding rate capability (70.29% capacitance retention with the current density increased from 1 to 50 mA/cm²) and superior cycling stability (92.94% of original capacity is retained after 5000 cycles at 10 mA/cm²). The prominent performance of NiCo₂S₄@NiCoP/NF electrode could be resulted from their unique hierarchical core-shell nanocolumn structure, which could offer abundant active sites near the interface for fast electrochemical reaction, and validly avoid the collapse of internal structure for the stability of whole structure in the repeated electrochemical measurement. The novel NiCo₂S₄@NiCoP/NF electrode offers a new method for future electrochemical energy storage devices with high-stability.

One-step synthesis of hollow C-NiCo2S4 nanostructures for high-performance supercapacitor electrodes

Carbon-containing NiCo2S4 hollow-nanoflake structures were fabricated by a one-step solvothermal method using CS2 as a single source for sulfidation and carbonization. The reaction mechanism for the hollow structure with carbon residues was explored based on the formation of a bis(dithiocarbamate)-metal complex and the Kirkendall effect during solvothermal synthesis. The NiCo2S4 nanoflake electrode exhibited a high specific capacitance of 1722 F g-1 (specific capacity 688.8 C g-1) at a current density of 1 A g-1 and an excellent cycling stability (capacity retention of 98.8% after 10 000 cycles). The as-fabricated asymmetric supercapacitor based on NiCo2S4 nanoflakes and activated carbon electrodes revealed a high energy density of 38.3 W h kg-1 and a high power density of 8.0 kW kg-1 with a capacitance retention of 91.5% and a coulombic efficiency of 95.6% after 5000 cycles, highlighting its great potential for practical supercapacitor applications.

Folic acid-functionalized graphene quantum dots with tunable fluorescence emission for cancer cell imaging and optical detection of Hg2+

Functional groups may alter the optical and electrical characteristics of graphene quantum dots and lead to unusual properties and related applications.

Direct aqueous solution synthesis of an ultra-fine amorphous nickel–boron alloy with superior pseudocapacitive performance for advanced asymmetric supercapacitors

This study reports a facile aqueous solution synthesis of an ultrafine amorphous nickel–boron alloy and its applications as a novel positive electrode material for asymmetric supercapacitors.

Facile synthesis of a MnFe2O4/rGO nanocomposite for an ultra-stable symmetric supercapacitor

A symmetric supercapacitor based on a MnFe₂O₄/rGO nanocomposite prepared from expanded graphite.