Graphene / V2O5 hybrid electrode for an asymmetric supercapacitor with high energy density in an organic electrolyte

Enhanced photocatalytic activity of V3O7 / V2O5 - reduced graphene oxide nanocomposite towards methylene blue dye degradation

This work investigates the photocatalytic performance of V2O5 and V3O7 nanoparticles and their nanocomposites with rGO. The as-annealed V2O5 and V3O7 nanoparticles exhibited pure orthorhombic and monoclinic structures with an optical bandgap of 2.3 and 2.5 eV, respectively. The corresponding vibrational modes using Raman and FTIR spectroscopy analysis further confirm the form. The morphological studies reveal that V2O5 and V3O7 nanoparticles possess plate and petal-like morphology, respectively. Moreover, in the case of V2O5/V3O7-rGO nanocomposites, the plate/petal-like nanoparticles are embedded within rGO sheets. Incorporating nanoparticles within rGO sheets has quenched the green photoluminescence emission, enhancing their photocatalytic performance upon irradiation with white light of 100 mW/cm2. This is ascribed to the effective transport of interfacial electrons from vanadium oxide nanoparticles to the rGO surface, reducing the recombination of photogenerated charge carriers. These results indicate that the vanadium oxide/rGO nanocomposites have potential applications in wastewater treatment.

Carbon-Hybridized Hydroxides for Energy Conversion and Storage: Interface Chemistry and Manufacturing

Carbon-hybridized hydroxides (CHHs) have been intensively investigated for uses in the energy conversion/storage fields. Nevertheless, the intrinsic structure-activity relationships between carbon and hydroxides within CHHs are still blurry, which hinders the fine modulation of CHHs in terms of practical applications to some degree. This review aims to figure out the intrinsic role of carbon materials in CHHs with a focus on the interface chemistry and the engineering strategy in-between two components. The fundamental effects of the carbon materials in enhancing the charge/mass transfer kinetics are first analyzed, particularly the extra electron pathways for fast charge transfer and the anchoring sites for boosting the mass transfer. Subsequently, the surface-guided/confined effects of carbon materials in CHHs to modify the morphology and tailor the hydroxides, and functional heterojunction for regulating the inner electronic structure are decoupled. The methods to efficiently construct a stable yet robust solid-solid heterointerface are summarized, including oxygen functional groups engrafting, topological defective sites construction and heteroatom incorporation to activate the inert carbon surface. The smart CHHs in some typical energy applications are demonstrated. Additionally, the methodologies that can reveal the hybridization electron configuration between two components are summed up. At last, the perspective and challenges faced by the CHHs for energy-related applications are outlined.

Vanadium Oxide: Phase Diagrams, Structures, Synthesis, and Applications

Vanadium oxides with multioxidation states and various crystalline structures offer unique electrical, optical, optoelectronic and magnetic properties, which could be manipulated for various applications. For the past 30 years, significant efforts have been made to study the fundamental science and explore the potential for vanadium oxide materials in ion batteries, water splitting, smart windows, supercapacitors, sensors, and so on. This review focuses on the most recent progress in synthesis methods and applications of some thermodynamically stable and metastable vanadium oxides, including but not limited to V₂O₃, V₃O₅, VO₂, V₃O₇, V₂O₅, V₂O₂, V₆O₁₃, and V₄O₉. We begin with a tutorial on the phase diagram of the V-O system. The second part is a detailed review covering the crystal structure, the synthesis protocols, and the applications of each vanadium oxide, especially in batteries, catalysts, smart windows, and supercapacitors. We conclude with a brief perspective on how material and device improvements can address current deficiencies. This comprehensive review could accelerate the development of novel vanadium oxide structures in related applications.

Rational La-doped hematite as an anode and hydrous cobalt phosphate as a battery-type electrode for a hybrid supercapacitor

In recent years, modern appliances require high energy density with a burst power supply. Hybrid supercapacitors show high performance based on high energy density without compromising power density and stability over thousands of charge-discharge cycles. In this work, the optimized hybrid electrodes using lanthanum-doped hematite (lanthanum-doped iron oxide) noted as 7.5%La-HMT as a negative electrode and hydrous cobalt phosphate (CoPO) as a battery-type positive electrode have been successfully fabricated via a simple hydrothermal method and a facile co-precipitation method, respectively. The 7.5%La-HMT showed excellent electrochemical performance due to doping of rare-earth La³⁺ metal ions, resulting in improvised active sites and reduction in the equivalent resistance. The 7.5%La-HMT operated at a high potential window (0 to -1.2 V) with an ultra-high specific capacitance (S_p) of 1226.7 F g^-1 at 1 A g^-1 with capacitance retention of 89.3% over 1000 cycles. CoPO could be operated at a high working window (0 to 0.45 V) with a specific capacity of 121.7 mA h g^-1 at a current density of 2 A g^-1 with capacitance retention of 85.4% over 1000 cycles. The configured CoPO//KOH//10%La-HMT aqueous hybrid capacitor device (Aq-HSC) could be operated at a potential window of 1.6 V and delivered a maximum energy density (E.D) of 83.6 W h kg^-1 at a power density (P.D) of 3.2 kW kg^-1 with S_p of 235.0 F g^-1 at 2 A g^-1 and 89.0% S_p retention over 5000 cycles. The simplicity of the synthesis methods for CoPO and 7.5%La-HMT along with their superior super-capacitive properties make them suitable for advanced electrical devices and hybrid vehicles.

Recent Development in Vanadium Pentoxide and Carbon Hybrid Active Materials for Energy Storage Devices

With the increasing energy demand for portable electronics, electric vehicles, and green energy storage solutions, the development of high-performance supercapacitors has been at the forefront of energy storage and conversion research. In the past decade, many scientific publications have been dedicated to designing hybrid electrode materials composed of vanadium pentoxide (V2O5) and carbon nanomaterials to bridge the gap in energy and power of traditional batteries and capacitors. V2O5 is a promising electrode material owing to its natural abundance, nontoxicity, and high capacitive potential. However, bulk V2O5 is limited by poor conductivity, low porosity, and dissolution during charge/discharge cycles. To overcome the limitations of V2O5, many researchers have incorporated common carbon nanostructures such as reduced graphene oxides, carbon nanotubes, carbon nanofibers, and other carbon moieties into V2O5. The carbon components facilitate electron mobility and act as porous templates for V2O5 nucleation with an enhanced surface area as well as interconnected surface morphology and structural stability. This review discusses the development of various V2O5/carbon hybrid materials, focusing on the effects of different synthesis methods, V2O5/carbon compositions, and physical treatment strategies on the structure and electrochemical performance of the composite material as promising supercapacitor electrodes.

Hierarchical porous CeO2 micro rice-supported Ni foam binder-free electrode and its enhanced pseudocapacitor performance by a redox additive electrolyte

A hierarchical porous CeO₂ micro rice/NF binder free electrode was fabricated via a facile hydrothermal method and the electrochemical performances were enhanced by the addition of 0.2 M K₄[Fe(CN)₆] redox additive in a 3 M KOH electrolyte.

Oxygen-Plasma Surface Treatment of an Electrode Sheet Using Carbon from Japanese Distilled Liquor Waste for Double-layer Capacitors

Oxygen-plasma treatment was performed on an activated carbon sheet obtained from shochu (Japanese distilled liquor) waste using a high-frequency plasma generator. The capacitances of the activated carbon sheet electrode subjected to surface treatment were measured using cyclic voltammetry. The best results were obtained with a processing time of 60 min, an output power of 40 W, an interelectrode distance of 13 cm and an oxygen pressure of 40 Pa. The maximum capacitance was 247 F g−1. Investigation of the surface functional groups of the activated carbon sheet revealed that the oxygen-containing functional groups modified on the surface of the activated carbon sheet electrode contributed to the improvement in the capacitance. High-performance electric double-layer capacitors can be realized using the developed electrodes.

Boosting the energy storage performance of V2O5 nanosheets by intercalating conductive graphene quantum dots

2-Dimensional (2D) transition metal oxides are an emerging class of energy materials that offer a wide spectrum of potential applications in electrochemical energy storage. In this study, V2O5 nanosheets have been nano-engineered with 0D graphene quantum dots (GQDs) via a solvothermal treatment process, and they serve as an anode material to boost electrochemical energy storage properties. The interlayer embedded GQD endows V2O5 (VNS-GQD) with structural and compositional advantages for high-performance energy storage, including expanded interlayer distances between layers, fast electrochemical kinetics, and additional stability to buffer the volume variation. Moreover, the strong coupling effect between GQDs and VNS, an ultra-large interfacial area and enhanced electrical conductivity promote the intercalation pseudocapacitance. VNS-GQD exhibits the specific capacitance of 572 F g-1 at a current density of 1 A g-1 and retains 92% of the initial capacitance after 10 000 charge-discharge cycles. The asymmetric supercapacitor exhibits superior electrochemical performance at a voltage window of 1.5 V. The energy density is 31.25 W h kg-1 at the power density of 2.25 kW kg-1, and maintains a superior energy density of 20.62 W h kg-1 at the high power density of 14.86 kW kg-1. The results of this study can provide an avenue for fabricating nano-sandwiched composites by embedding GQDs into interlayers of 2D transition metal oxide for ultra-high performance applications of energy storage devices.

N-Doped Modified Graphene/Fe2O3 Nanocomposites as High-Performance Anode Material for Sodium Ion Storage

Sodium-ion storage devices have received widespread attention because of their abundant sodium resources, low cost and high energy density, which verges on lithium-ion storage devices. Electrochemical redox reactions of metal oxides offer a new approach to construct high-capacity anodes for sodium-ion storage devices. However, the poor rate performance, low Coulombic efficiency, and undesirable cycle stability of the redox conversion anodes remain a huge challenge for the practical application of sodium ion energy storage devices due to sluggish kinetics and irreversible structural change of most conversion anodes during cycling. Herein, a nitrogen-doping graphene/Fe₂O₃ (N-GF-300) composite material was successfully prepared as a sodium-ion storage anode for sodium ion batteries and sodium ion supercapacitors through a water bath and an annealing process, where Fe₂O₃ nanoparticles with a homogenous size of about 30 nm were uniformly anchored on the graphene nanosheets. The nitrogen-doping graphene structure enhanced the connection between Fe₂O₃ nanoparticles with graphene nanosheets to improve electrical conductivity and buffer the volume change of the material for high capacity and stable cycle performance. The N-GF-300 anode material delivered a high reversible discharge capacity of 638 mAh g⁻¹ at a current density of 0.1 A g⁻¹ and retained 428.3 mAh g⁻¹ at 0.5 A g⁻¹ after 100 cycles, indicating a strong cyclability of the SIBs. The asymmetrical N-GF-300//graphene SIC exhibited a high energy density and power density with 58 Wh kg⁻¹ at 1365 W kg⁻¹ in organic solution. The experimental results from this work clearly illustrate that the nitrogen-doping graphene/Fe₂O₃ composite material N-GF-300 is a potential feasibility for sodium-ion storage devices, which further reveals that the nitrogen doping approach is an effective technique for modifying carbon matrix composites for high reaction kinetics during cycles in sodium-ion storage devices and even other electrochemical storage devices.

Interfacial synthesis of micro-cuboid Ni0.55Co0.45C2O4 solid solution with enhanced electrochemical performance for hybrid supercapacitors

Efficient charge and energy storage relies essentially on the development of innovative electrode materials with enhanced electrochemical kinetics. Herein, Ni_0.55Co_0.45C₂O₄ solid solution was successfully synthesized by a liquid-liquid interfacial reaction. The observation of the morphologies of Ni_0.55Co_0.45C₂O₄ depicts a peculiar micro-cuboid structure composed of nanoparticles in the size range of 13 to 23 nm, benefiting the increase in the contribution of surface-controlled reactions to charge storage processes. The results from X-ray diffraction and thermogravimetric analysis demonstrate the similarity of the crystal structure and thermal decomposition behavior between Ni_0.55Co_0.45C₂O₄ and CoC₂O₄, and indicate that the CoC₂O₄ lattice plays a role as the fundamental framework in the solid solution instead of NiC₂O₄. The electrochemical measurements show that Ni_0.55Co_0.45C₂O₄ achieves a higher specific capacity of 562 C g^-1 at a current density of 1 A g^-1 than its counterpart NiC₂O₄/CoC₂O₄ hybrids, due to this the alternative arrangement of nickel and cobalt species in the solid solution expedites the diffusion process of active ions during the electrochemical reaction. Depending on the enhancement of the electrochemical stability in the solid solution, Ni_0.55Co_0.45C₂O₄ electrodes retain 87.4% of the initial capacity after 4000 cycles. The assembled Ni_0.55Co_0.45C₂O₄//AC hybrid supercapacitor attains an energy density of 38.5 W h kg^-1 at a power density of 799 W kg^-1 with a long cycling life (80% of the initial capacitance after 10 000 cycles). The excellent electrochemical performance suggests that Ni_0.55Co_0.45C₂O₄ is a promising candidate electrode material for supercapacitors.

Asymmetric supercapacitors with high energy densities

The low energy densities of supercapacitors (SCs) are generally limited by the used anodes. To develop SCs with high energy densities, Fe3+ modified V2O5@GQDs (m-V2O5@GQDs) and ZIF-67-derived nanoporous carbon loaded with Mn3O4 (C/N-Mn3O4) were synthesized. After their detailed characterization using electron microscopy, X-ray methods and electrochemical techniques, they were further utilized as the anode and the cathode, respectively, to construct asymmetric supercapacitors (ASCs). The as-synthesized m-V2O5@GQDs improve the poor conductivity of V2O5, contributing greatly to a specific capacitance of 761 F g-1 at a current density of 2 A g-1. With application of a cell voltage of 2 V, an energy density of up to 99.4 W h kg-1 is achieved at a power density of 1000 W kg-1. Such ASCs also exhibit outstanding cycling performance (95% of initial capacitance even after 10 000 charging/discharging cycles). This study thus provides a new way to design and construct ASCs with high energy densities.

Anchoring carbon layers and oxygen vacancies endow WO3−x/C electrode with high specific capacity and rate performance for supercapacitors

Herein, novel hierarchical carbon layer-anchored WO_3−x/C ultra-long nanowires were developed via a facile solvent-thermal treatment and a subsequent rapid carbonization process. The inner anchored carbon layers and abundant oxygen vacancies endowed the WO_3−x/C nanowire electrode with high conductivity, as measured with a single nanowire, which greatly enhanced the redox reaction active sites and rate performance. Surprisingly, the WO_3−x/C electrode exhibited outstanding specific capacitance of 1032.16 F g⁻¹ at the current density of 1 A g⁻¹ in a 2 M H₂SO₄ electrolyte and maintained the specific capacitance of 660 F g⁻¹ when the current density increased to 50 A g⁻¹. Significantly, the constructed WO_3−x/C//WO_3−x/C symmetric supercapacitors achieved specific capacitance of 243.84 F g⁻¹ at the current density of 0.5 A g⁻¹ and maintained the capacitance retention of 94.29% after 5000 charging/discharging cycles at the current density of 4 A g⁻¹. These excellent electrochemical performances resulted from the fascinating structure of the WO_3−x/C nanowires, showing a great potential for future energy storage applications.

A high-performance supercapacitor electrode comprising hierarchical carbon layer-anchored WO_3−x/C nanowires with inner abundant redox reaction active sites and numerous oxygen vacancies is presented.