Graphene-quantum-dots induced NiCo2S4 with hierarchical-like hollow nanostructure for supercapacitors with enhanced electrochemical performance

Machine Learning a Predictive Tool for the Analysis of NiCo2S4/Graphene Composites for Supercapacitor

Nickel cobalt sulfide (NiCo2S4) has considerable potential electrode material for supercapacitors owing to its distinct physical and chemical characteristics. However, the practical applications of pristine NiCo2S4 have been limited by issues such as small specific surface area, agglomeration, and volume changes during cycling, leading to low specific capacitance/capacity and cyclic stability at high rates. Several efforts have been taken to address these challenges. Among those the design and development of NiCo2S4-graphene-based composites have been widely investigated. This review explores the effect of NiCo2S4 architecture and its nanocomposite with graphene on the electrochemical properties. How the various preparative parameters such as synthesis methods, precursors, experimental conditions contributed to efficiently accelerating charge transport kinetics is outlined. Finally, the effect of introduction of graphene on the electrochemical performance of NiCo2S4 is discussed using density functional theory (DFT). Also, machine learning (ML) models are used to analyze the specific capacitance variation with respect to different synthesis parameters, morphology, energy density, and power density. ML models identify limitations and scope of work for working on NiCo2S4/graphene composites. It is found that most influencing parameter is annealing time that can alter specific capacitance. The review outlines future research directions, challenges, and opportunities in NiCo2S4/graphene-based supercapacitor.

Dual-Driven Activation of High-Valence States in Prussian Blue Analogues Via Graphene-Quantum Dots and Ozone-Induced Surface Restructuring for Superior Hydrogen Evolution Electrocatalyst

Electrochemical water splitting is a pivotal process for sustainable hydrogen energy production, relying on efficient hydrogen evolution reaction (HER) catalysts, particularly in acidic environments, where both high activity and durability are crucial. Despite the favorable kinetics of platinum (Pt)-based materials, their performance is hindered under harsh conditions, driving the search for alternatives. Due to their unique structural characteristic, Prussian blue analogs (PBAs) emerge as attractive candidates for designing efficient HER electrocatalysts. However, modulating their properties and functionalities is crucial to overcome their conductivity issue. Herein, a reconfiguration strategy for the dual-driven surface restructuring of the CoFe PBA involving graphene quantum dots (GQD) and UV/ozone is proposed. X-ray absorption spectroscopy (XAS) analysis revealed that dual-driven reconstruction plays a pivotal role in promoting the high-valence metal ions, effectively reducing charge transfer resistance-a key limitation in HER. The optimized CoFe PBA/GQD-UV exhibits remarkable electrocatalytic performance toward HER, with a low overpotential of 77 mV to reach a current density of 10 mA cm-2 with excellent durability for 12 h under an extremely high current density of 500 mA cm-2 in an acidic solution. This dual-combination strategy offering a new pathway to develop highly active electrocatalysts.

Lignin-Based N-Carbon Dots Anchoring NiCo2S4/Graphene Hydrogel Exhibits Excellent Performance as Anodes for Hybrid Supercapacitor

A NiCo2S4/N-CDs/RGO ternary composite hydrogel was prepared via a one-step hydrothermal method, utilizing lignin-based nitrogen-doped carbon dots as a bridge connecting NiCo2S4 and graphene. The specific capacitance of NiCo2S4/N-CDs/RGO significantly outperforms that of the GH and NiCo2S4/RGO electrodes, achieving 1050 F g-1. The 3D mesh porous hydrogel structure mitigates NiCo2S4 nanoparticle aggregation, providing a larger specific surface area for enhanced charge storage. The abundant functional groups of N-CDs interact with Ni (II) and Co (III) cations, favoring NiCo2S4 particle synthesis. Additionally, an assembled solid-state asymmetric supercapacitor employing NiCo2S4/N-CDs/RGO as the positive electrode exhibited excellent energy density (68.4 Wh kg-1) and cycle stability (82% capacitance retention after 10,000 constant current charge-discharge cycles).

Surface restructuring Prussian blue analog-derived bimetallic CoFe phosphides by N-doped graphene quantum dots for electroactive hydrogen evolving catalyst

As a crucial stage of electrochemical water splitting, hydrogen evolution reaction (HER) favour catalyst to attain rapid kinetics for its broader application, alternating Pt in the acidic environment. Transition metal phosphides (TMPs) are one kind of earth-abundant, nonprecious-based catalyst which has been classified as a viable alternative and active for HER. While the performance remains inferior to Pt which primarily targets durability under high current density, pinpointing the reconfiguration strategy would be critical to their catalytic competency. Herein, we reported engineered N-doped graphene quantum dots (NGQD) on the surface of bimetallic CoFe phosphide (CoFeP) derived from cobalt iron Prussian blue analogue (CoFePBA) as an efficient HER. By introducing the NGQD, the surface architect and electronic state of the transition metal are altered through an adjusted electronic configuration and thus, improving the electrocatalytic activity for HER. The X-ray absorption spectroscopy (XAS) highlighting the role of NGQD, which successfully induced the electron density of Co atoms, further expedites its conductivity and electroactivity. The optimized NGQD/CoFeP substantially surpasses an overpotential of 70 mV (vs. RHE) at the current density of 10 mA cm-2 in 0.5 M H2SO4. Furthermore, the NGQD/CoFeP maintains its exceptional stability under an extremely high current density of 600 mA cm-2 after 12 h of continuous operation. Our findings show that NGQD/CoFeP might demonstrate as a viable alternative to the conventional Pt electrocatalyst in commercial water splitting for hydrogen generation.

Emerging Trends of Carbon-Based Quantum Dots: Nanoarchitectonics and Applications

Carbon-based quantum dots (QDs) have emerged as a fascinating class of advanced materials with a unique combination of optoelectronic, biocompatible, and catalytic characteristics, apt for a plethora of applications ranging from electronic to photoelectrochemical devices. Recent research works have established carbon-based QDs for those frontline applications through improvements in materials design, processing, and device stability. This review broadly presents the recent progress in the synthesis of carbon-based QDs, including carbon QDs, graphene QDs, graphitic carbon nitride QDs and their heterostructures, as well as their salient applications. The synthesis methods of carbon-based QDs are first introduced, followed by an extensive discussion of the dependence of the device performance on the intrinsic properties and nanostructures of carbon-based QDs, aiming to present the general strategies for device designing with optimal performance. Furthermore, diverse applications of carbon-based QDs are presented, with an emphasis on the relationship between band alignment, charge transfer, and performance improvement. Among the applications discussed in this review, much focus is given to photo and electrocatalytic, energy storage and conversion, and bioapplications, which pose a grand challenge for rational materials and device designs. Finally, a summary is presented, and existing challenges and future directions are elaborated.

Advances in preparation, mechanism and applications of graphene quantum dots/semiconductor composite photocatalysts: A review

Due to the low efficiency of single-component nano materials, there are more and more studies on high-efficiency composites. As zero dimensional (0D) non-metallic semiconductor material, the emergence of graphene quantum dots (GQDs) overcomes the shortcomings of traditional photocatalysts (rapid rate of electron-hole recombination and narrow range of optical response). Their uniqueness is that they can combine the advantages of quantum dots (rich functional groups at edge) and sp² carbon materials (large specific surface area). The inherent inert carbon stabilizes chemical and physical properties, and brings new breakthroughs to the development of benchmark photocatalysts. The photocatalytic efficiency of GQDs composite with semiconductor materials (SCs) can be improved by the following three points: (1) accelerating charge transfer, (2) extending light absorption range, (3) increasing active sites. The methods of preparation (bottom-up and top-down), types of heterojunctions, mechanisms of photocatalysis, and applications of GQDs/SCs (wastewater treatment, energy storage, gas sensing, UV detection, antibiosis and biomedicine) are comprehensively discussed. And it is hoped that this review can provide some guidance for the future research on of GQDs/SCs on photocatalysis.

Recent Developments of Transition Metal Compounds-Carbon Hybrid Electrodes for High Energy/Power Supercapacitors

Due to their rapid power delivery, fast charging, and long cycle life, supercapacitors have become an important energy storage technology recently. However, to meet the continuously increasing demands in the fields of portable electronics, transportation, and future robotic technologies, supercapacitors with higher energy densities without sacrificing high power densities and cycle stabilities are still challenged. Transition metal compounds (TMCs) possessing high theoretical capacitance are always used as electrode materials to improve the energy densities of supercapacitors. However, the power densities and cycle lives of such TMCs-based electrodes are still inferior due to their low intrinsic conductivity and large volume expansion during the charge/discharge process, which greatly impede their large-scale applications. Most recently, the ideal integrating of TMCs and conductive carbon skeletons is considered as an effective solution to solve the above challenges. Herein, we summarize the recent developments of TMCs/carbon hybrid electrodes which exhibit both high energy/power densities from the aspects of structural design strategies, including conductive carbon skeleton, interface engineering, and electronic structure. Furthermore, the remaining challenges and future perspectives are also highlighted so as to provide strategies for the high energy/power TMCs/carbon-based supercapacitors.

Carbon-Based Quantum Dots for Supercapacitors: Recent Advances and Future Challenges

Carbon-based Quantum dots (C-QDs) are carbon-based materials that experience the quantum confinement effect, which results in superior optoelectronic properties. In recent years, C-QDs have attracted attention significantly and have shown great application potential as a high-performance supercapacitor device. C-QDs (either as a bare electrode or composite) give a new way to boost supercapacitor performances in higher specific capacitance, high energy density, and good durability. This review comprehensively summarizes the up-to-date progress in C-QD applications either in a bare condition or as a composite with other materials for supercapacitors. The current state of the three distinct C-QD families used for supercapacitors including carbon quantum dots, carbon dots, and graphene quantum dots is highlighted. Two main properties of C-QDs (structural and electrical properties) are presented and analyzed, with a focus on the contribution to supercapacitor performances. Finally, we discuss and outline the remaining major challenges and future perspectives for this growing field with the hope of stimulating further research progress.

Graphene Quantum Dots as Flourishing Nanomaterials for Bio-Imaging, Therapy Development, and Micro-Supercapacitors

Graphene quantum dots (GQDs) are considerably a new member of the carbon family and shine amongst other members, thanks to their superior electrochemical, optical, and structural properties as well as biocompatibility features that enable us to engage them in various bioengineering purposes. Especially, the quantum confinement and edge effects are giving GQDs their tremendous character, while their heteroatom doping attributes enable us to specifically and meritoriously tune their prospective characteristics for innumerable operations. Considering the substantial role offered by GQDs in the area of biomedicine and nanoscience, through this review paper, we primarily focus on their applications in bio-imaging, micro-supercapacitors, as well as in therapy development. The size-dependent aspects, functionalization, and particular utilization of the GQDs are discussed in detail with respect to their distinct nano-bio-technological applications.

Graphene quantum dot based materials for sensing, bio-imaging and energy storage applications: a review

Graphene quantum dots (GQDs) are an attractive nanomaterial consisting of a monolayer or a few layers of graphene having excellent and unique properties. GQDs are endowed with the properties of both carbon dots (CDs) and graphene. This review addresses applications of GQD based materials in sensing, bioimaging and energy storage. In the first part of the review, different approaches of GQD synthesis such as top-down and bottom-up synthesis methods have been discussed. The prime focus of this review is on green synthesis methods that have also been applied to the synthesis of GQDs. The GQDs have been discussed thoroughly for all the aspects along with their potential applications in sensors, biomedicine, and energy storage systems. In particular, emphasis is given to popular applications such as electrochemical and photoluminescence (PL) sensors, electrochemiluminescence (ECL) sensors, humidity and gas sensors, bioimaging, lithium-ion (Li-ion) batteries, supercapacitors and dye-sensitized solar cells. Finally, the challenges and the future perspectives of GQDs in the aforementioned application fields have been discussed.

Graphene quantum dots (GQDs) are an attractive nanomaterial consisting of a monolayer or a few layers of graphene having excellent and unique properties.

Novel approach to synthesize NiCo2S4 composite for high-performance supercapacitor application with different molar ratio of Ni and Co

Here, we developed a new approach to synthesize NiCo2S4 thin films for supercapacitor application using the successive ionic layer adsorption and reaction (SILAR) method on Ni mesh with different molar ratios of Ni and Co precursors. The five different NiCo2S4 electrodes affect the electrochemical performance of the supercapacitor. The NiCo2S4 thin films demonstrate superior supercapacitance performance with a significantly higher specific capacitance of 1427 F g-1 at a scan rate of 20 mV s-1. These results indicate that ternary NiCo2S4 thin films are more effective electrodes compared to binary metal oxides and metal sulfides.

In situ self-assembly of Ni3S2/MnS/CuS/reduced graphene composite on nickel foam for high power supercapacitors

Transition metal sulfides (TMS), as promising electroactive materials for asymmetric supercapacitors, have been limited due to their relatively poor conductivity and cycle stability. Here ternary Ni₃S₂/MnS/CuS composites were assembled in situ on nickel foam (NF) using a hydrothermal method via electrostatic adsorption of Ni⁺, Mn²⁺ and Cu²⁺ ions on a reduced graphene (rGO) nanosheet template. The chemical structure was characterized by various analytic methods. Ni₃S₂/MnS/CuS has spherical morphology assembled from closely packed nanosheets, while Ni₃S₂/MnS/CuS@rGO has a three-dimensional porous spherical structure with much lower diameter because rGO nanosheets can play the role of a template to induce the growth of Ni₃S₂/MnS/CuS. At a current density of 1 A g⁻¹, the specific capacitance was obtained to be 1028 F g⁻¹ for Ni₃S₂/MnS/CuS, 628.6 F g⁻¹ for Ni₃S₂/MnS@rGO, and 2042 F g⁻¹ for Ni₃S₂/MnS/CuS@rGO, respectively. Charge transfer resistance (R_ct) of Ni₃S₂/MnS/CuS@rGO (0.001 Ω) was much lower than that of Ni₃S₂/MnS@rGO by 0.02 Ω, and lower than that of Ni₃S₂/MnS/CuS by 0.017 Ω. After 5000 cycles, the Ni₃S₂–MnS–CuS@RGO electrode maintains 78.3% of the initial capacity at 20 A g⁻¹. An asymmetric supercapacitor was subsequently assembled using Ni₃S₂/MnS/CuS@rGO as the positive electrode and rGO as the negative electrode. The specific capacitance of asymmetric batteries was maintained at 90.8% of the initial state after 5000 GCD.

Transition metal sulfides (TMS), as promising electroactive materials for asymmetric supercapacitors, have been limited due to their relatively poor conductivity and cycle stability.