Structuring graphene quantum dots anchored CuO for high-performance hybrid supercapacitors

Recent Progress on Graphene-Based Derivatives for Enhanced Energy Storage Devices

2D materials have been widely utilized in efficient energy storage applications in recent years. In efforts to mitigate global warming concerns, the novel trends of using nonfossil fuel cells have drawn significant attention of scientific communities towards various 2D materials owing to their excellent physiochemical properties, preferably suitable for developing energy storage systems. Amongst the 2D materials, graphene and its derivatives, due to their tunable surface properties, have emerged as prominent 2D materials for energy storage. Graphene, leveraged with its highly reactive surface sites, can be tailored with myriads of functional groups to enhance its applicability as an energy storage material. This review focuses on the recent advancements in utilizing various dimensions of graphene, including 0D GQDs, 1D GNRs, 2D GO/rGO, and 3D architectures, along with vertical graphene and graphene paper for efficient energy storage devices. The review addresses the limitations of pristine graphene and highlights the benefits of functionalization and synergistic material combinations. This also discusses the challenges and future perspectives related to the commercialization and large-scale production of graphene-based energy storage devices.

Surface Engineering of Copper Foam to Construct a Hierarchical Heterostructure for High Energy Efficient Supercapacitors

As a unique pseudocapacitive material, the heterojunction-structured CuO@Cu combines the high conductivity of substrate Cu and the high capacity of active CuO together for structure-integral electrodes, however, its structural optimization and improved capacity are still the main challenges so far. In this study, an initial surface etching of copper foam (CF) is adopted to construct a primary heterostructure of CuO nanowires@CF (CuO NW@CF), and then, the surface decoration of CuO NW@CF via the deposition of cerium-2-methylimidazole based metal-organic frameworks (Ce-2MI) finally results in the current-collector-/binder-free electrodes of the hierarchical heterostructure Ce-2MI@CuO NW@CF. Compared to the structural properties of CuO NW@CF, both the introducing Ce-ion active sites and the enriched lattice oxygen vacancies cooperatively endow the pseudocapacitive electrodes of Ce-2MI@CuO NW@CF with a ultrahigh specific capacitance and excellent cycling stability. Within the potential window of 1.6 V, the asymmetric supercapacitor devices of activated carbon//Ce-2MI@CuO NW@CF acquire a high energy density of 56.8 Wh kg-1 at 725 W kg-1, which can light up a light-emitting diode (LED) bulb for 20 min. Therefore, constructing the hierarchically heterostructured Ce-2MI@CuO NW@CF is an effective approach to developing high-performance supercapacitors for potential application purposes.

Unveiling the Promoting Mechanism of H2 Activation on CuFeOx Catalyst for Low-Temperature CO Oxidation

The effect of H2 activation on the performance of CuFeOx catalyst for low-temperature CO oxidation was investigated. The characterizations of XRD, XPS, H2-TPR, O2-TPD, and in situ DRIFTS were employed to establish the relationship between physicochemical property and catalytic activity. The results showed that the CuFeOx catalyst activated with H2 at 100 °C displayed higher performance, which achieved 99.6% CO conversion at 175 °C. In addition, the H2 activation promoted the generation of Fe2+ species, and more oxygen vacancy could be formation with higher concentration of Oα species, which improved the migration rate of oxygen species in the reaction process. Furthermore, the reducibility of the catalyst was enhanced significantly, which increased the low-temperature activity. Moreover, the in situ DRIFTS experiments revealed that the reaction pathway of CO oxidation followed MvK mechanism at low temperature (<175 °C), and both MvK and L-H mechanism was involved at high temperature. The Cu+-CO and carbonate species were the main reactive intermediates, and the H2 activation increased the concentration of Cu+ species and accelerated the decomposition carbonate species, thus improving the catalytic performance effectively.

Interfacial Interaction in MeOx/MWNTs (Me-Cu, Ni) Nanostructures as Efficient Electrode Materials for High-Performance Supercapacitors

Due to their unique physical and chemical properties, complex nanostructures based on carbon nanotubes and transition metal oxides are considered promising electrode materials for the fabrication of high-performance supercapacitors with a fast charge rate, high power density, and long cycle life. The crucial role in determining their efficiency is played by the properties of the interface in such nanostructures, among them, the type of chemical bonds between their components. The complementary theoretical and experimental methods, including dispersion-corrected density functional theory (DFT-D3) within GGA-PBE approximation, scanning electron microscopy (SEM), X-ray diffraction (XRD), Raman, X-ray photoelectron, and X-ray absorption spectroscopies, were applied in the present work for the comprehensive investigation of surface morphology, structure, and electronic properties in CuOx/MWCNTs and NiOx/MWCNTs. As a result, the type of interfacial interaction and its correlation with electrochemical characteristics were determined. It was found that the presence of both Ni-O-C and Ni-C bonds can increase the contact between NiO and MWCNTs, and, through this, promote electron transfer between NiO and MWCNTs. For NiOx/MWCNTs, better electrochemical characteristics were observed than for CuOx/MWCNTs, in which the interfacial interaction is determined only by bonding through Cu-O-C bonds. The electrochemical properties of CuOx/MWCNTs and NiOx/MWCNTs were studied to demonstrate the effect of interfacial interaction on their efficiency as electrode materials for supercapacitor applications.

Chemical synthesis and super capacitance performance of novel CuO@Cu4O3/rGO/PANI nanocomposite electrode

Copper oxide-based nanocomposites are promising electrode materials for high-performance supercapacitors due to their unique properties that aid electrolyte access and ion diffusion to the electrode surface. Herein, a facile and low-cost synthesis in situ strategy based on co-precipitation and incorporation processes of reduced graphene oxide (rGO), followed by in situ oxidative polymerization of aniline monomer has been reported. CuO@Cu4O3/rGO/PANI nanocomposite revealed the good distribution of CuO@Cu4O3 and rGO within the polymer matrix which allows improved electron transport and ion diffusion process. Galvanostatic charge-discharge (GCD) results displayed a higher specific capacitance value of 508 F g-1 for CuO@Cu4O3/rGO/PANI at 1.0 A g-1 in comparison to the pure CuO@Cu4O3 278 F g-1. CuO@Cu4O3/rGO/PANI displays an energy density of 23.95 W h kg-1 and power density of 374 W kg-1 at the current density of 1 A g-1 which is 1.8 times higher than that of CuO@Cu4O3 (13.125 W h kg-1) at the same current density. The retention of the electrode was 93% of its initial capacitance up to 5000 cycles at a scan rate of 100 mV s-1. The higher capacitance of the CuO@Cu4O3/rGO/PANI electrode was credited to the formation of a fibrous network structure and rapid ion diffusion paths through the nanocomposite matrix that resulted in enhanced surface-dependent electrochemical properties.

Engineering functionalization and properties of graphene quantum dots (GQDs) with controllable synthesis for energy and display applications

Graphene quantum dots (GQDs), a new type of 0D nanomaterial, are composed of a graphene lattice with sp2 bonding carbon core and characterized by their abundant edges and wide surface area. This unique structure imparts excellent electrical properties and exceptional physicochemical adsorption capabilities to GQDs. Additionally, the reduction in dimensionality of graphene leads to an open band gap in GQDs, resulting in their unique optical properties. The functional groups and dopants in GQDs are key factors that allow the modulation of these characteristics. So, controlling the functionalization level of GQDs is crucial for understanding their characteristics and further application. This review provides an overview of the properties and structure of GQDs and summarizes recent developments in research that focus on their controllable synthesis, involving functional groups and doping. Additionally, we provide a comprehensive and focused explanation of how GQDs have been advantageously applied in recent years, particularly in the fields of energy storage devices and displays.

Optimum iron-pyrophosphate electronic coupling to improve electrochemical water splitting and charge storage

Tuning the electronic properties of transition metals using pyrophosphate (P2O7) ligand moieties can be a promising approach to improving the electrochemical performance of water electrolyzers and supercapacitors, although such a material's configuration is rarely exposed. Herein, we grow NiP2O7, CoP2O7, and FeP2O7 nanoparticles on conductive Ni-foam using a hydrothermal procedure. The results indicated that, among all the prepared samples, FeP2O7 exhibited outstanding oxygen evolution reaction and hydrogen evolution reaction with the least overpotential of 220 and 241 mV to draw a current density of 10 mA/cm2. Theoretical studies indicate that the optimal electronic coupling of the Fe site with pyrophosphate enhances the overall electronic properties of FeP2O7, thereby enhancing its electrochemical performance in water splitting. Further investigation of these materials found that NiP2O7 had the highest specific capacitance and remarkable cycle stability due to its high crystallinity as compared to FeP2O7, having a higher percentage composition of Ni on the Ni-foam, which allows more Ni to convert into its oxidation states and come back to its original oxidation state during supercapacitor testing. This work shows how to use pyrophosphate moieties to fabricate non-noble metal-based electrode materials to achieve good performance in electrocatalytic splitting water and supercapacitors.

Probing the Förster Resonance Energy Transfer Dynamics in Colloidal Donor-Acceptor Quantum Dots Assemblies

In this article, we report the synthesis of graphene quantum dots (GQDs) by hydrothermal method and surface modified CdS quantum dots (QDs) via the colloidal method and the fabrication of their dyad. The CdS QDs functionalized by mercaptoacetic acid (MAA) attach to the GQDs via electrostatic interactions. Spectral overlapping between the emission spectrum of GQDs and the absorption spectrum of CdS QDs allows efficient Förster resonance energy transfer (FRET) from GQDs to the CdS QDs in the GQDs-CdS QDs dyads. The magnitude of FRET efficiency (E) and the rate of energy transfer (kE) assessed by the photoluminescence (PL) decay kinetics are ~61.84% and ⁓3.8 × 108 s- 1, respectively. These high values of FRET efficiency and energy transfer rate can be assigned to the existence of strong electrostatic interactions between GQDs and CdS QDs, which arise due to the presence of polar functionalities on the surface of both GQDs and CdS QDs. The understanding of energy transfer in the luminescent donor-acceptor FRET system is of significant importance and the practical implications of such FRET systems could overall improve the efficiency of photovoltaics, sensing, imaging and optoelectronic devices.

Bi-Fe chalcogenides anchored carbon matrix and structured core-shell Bi-Fe-P@Ni-P nanoarchitectures with appealing performances for supercapacitors

Pseudocapacitive materials based on multi-active components are attractive platforms for future portable energy devices due to their excellent redox processes and low cost. In this study, nanostructured bismuth-iron chalcogenide anchored on multiwalled carbon nanotube framework (Bi-Fe chalcogenide/C)-based electrode materials were fabricated via a simple solvothermal protocol with enhanced electrochemical performances. The obtained Bi-Fe chalcogenide/C nanocomposites combining the improved electroconductivity of carbonic frameworks and high pseudocapacitive properties of Bi/Fe reversible redox processes were employed as negative electrodes for asymmetric supercapacitor (ASC) devices. Systematic investigation of the synthesized materials and capacitive performance indicated that the Bi-Fe-P/C electrode simultaneously achieved an intrinsically appreciable specific capacitance of 532 F g^-1 at a current density of 1 A g^-1, high-rate capability, and cyclic stability, profiting from the structural and amorphous merits as well as the collaborative effect of multiple components. Besides, we employed an effective strategy to graft Bi-Fe-P film on a self-standing nickel phosphide (Ni-P) to manufacture a cathode with superior capacitive performances. The as-prepared core-shell Bi-Fe-P@Ni-P was used as a high-performance positive electrode and displayed a large specific capacitance of 230.6 mAh g^-1 at 1 A g^-1. Additionally, we also assembled an ASC system using the core-shell Bi-Fe-P@Ni-P as a positive electrode and amorphous Bi-Fe-P/C as a negative electrode with an expanded operational potential of 1.6 V. The hybrid device delivered a high specific energy density of 81.5 Wh kg^-1 at a power density of 890.2 W kg^-1 together with good cyclic characteristics (85.6% capacitance retention after 8000 consecutive cycles). The obtained findings offer new insights into the design of advanced energy storage materials at relatively low costs and underscore the proficiency of heterostructured multicomponent electrodes as a practical option for enhancing the electrochemical performance of ASC.

An asymmetric supercapacitor with an interpenetrating crystalline Fe-MOF as the positive electrode and its congenetic derivative as the negative electrode

Interpenetrating crystalline Fe-based materials of FeSC and congenetic derivative FeSC# have been assembled into an asymmetric supercapacitor, which can offer an excellent supercapacitor performance.