Quinone-Decorated Onion-Like Carbon/Carbon Fiber Hybrid Electrodes for High-Rate Supercapacitor Applications

Synthesis and Applications of Nanostructured Hollow Transition Metal Chalcogenides

Nanostructures with well-defined structures and rich active sites occupy an important position for efficient energy storage and conversion. Recent studies have shown that a transition metal chalcogenide (TMC) has a unique structure, such as diverse structural morphology, excellent stability, high efficiency, etc., and is used in the fields of electrochemistry and catalysis. The nanohollow structure metal chalcogenide has broad application prospects due to the existence of a large number of active sites and a wide internal space, allowing a large number of ions and electrons to be transported. Summarizing synthetic strategies of nanostructured hollow transition metal sulfides (HTMC) and their applications in the field of energy storage and conversion is discussed here. Through some representative examples, the fabrication and properties of various hollow structures are analyzed, which prompt some emerging nanoengineering designs to be applied to transition metal chalcogenides. It is hoped that the construction of the HTMC will lead to a deeper understanding for the further exploration of energy storage and conversion.

Titanium Niobium Oxide Ti2 Nb10 O29 /Carbon Hybrid Electrodes Derived by Mechanochemically Synthesized Carbide for High-Performance Lithium-Ion Batteries

This work introduces the facile and scalable two-step synthesis of Ti₂ Nb₁₀ O₂₉ (TNO)/carbon hybrid material as a promising anode for lithium-ion batteries (LIBs). The first step consisted of a mechanically induced self-sustaining reaction via ball-milling at room temperature to produce titanium niobium carbide with a Ti and Nb stoichiometric ratio of 1 to 5. The second step involved the oxidation of as-synthesized titanium niobium carbide to produce TNO. Synthetic air yielded fully oxidized TNO, while annealing in CO₂ resulted in TNO/carbon hybrids. The electrochemical performance for the hybrid and non-hybrid electrodes was surveyed in a narrow potential window (1.0-2.5 V vs. Li/Li⁺ ) and a large potential window (0.05-2.5 V vs. Li/Li⁺ ). The best hybrid material displayed a specific capacity of 350 mAh g^-1 at a rate of 0.01 A g^-1 (144 mAh g^-1 at 1 A g^-1 ) in the large potential window regime. The electrochemical performance of hybrid materials was superior compared to non-hybrid materials for operation within the large potential window. Due to the advantage of carbon in hybrid material, the rate handling was faster than that of the non-hybrid one. The hybrid materials displayed robust cycling stability and maintained ca. 70 % of their initial capacities after 500 cycles. In contrast, only ca. 26 % of the initial capacity was maintained after the first 40 cycles for non-hybrid materials. We also applied our hybrid material as an anode in a full-cell lithium-ion battery by coupling it with commercial LiMn₂ O₄ .

Recent Progress on Organic Electrodes Materials for Rechargeable Batteries and Supercapacitors

Rechargeable batteries are essential elements for many applications, ranging from portable use up to electric vehicles. Among them, lithium-ion batteries have taken an increasing importance in the day life. However, they suffer of several limitations: safety concerns and risks of thermal runaway, cost, and high carbon footprint, starting with the extraction of the transition metals in ores with low metal content. These limitations were the motivation for an intensive research to replace the inorganic electrodes by organic electrodes. Subsequently, the disadvantages that are mentioned above are overcome, but are replaced by new ones, including the solubility of the organic molecules in the electrolytes and lower operational voltage. However, recent progress has been made. The lower voltage, even though it is partly compensated by a larger capacity density, may preclude the use of organic electrodes for electric vehicles, but the very long cycling lives and the fast kinetics reached recently suggest their use in grid storage and regulation, and possibly in hybrid electric vehicles (HEVs). The purpose of this work is to review the different results and strategies that are currently being used to obtain organic electrodes that make them competitive with lithium-ion batteries for such applications.

A Review of Supercapacitors Based on Graphene and Redox-Active Organic Materials

Supercapacitors are a highly promising class of energy storage devices due to their high power density and long life cycle. Conducting polymers (CPs) and organic molecules are potential candidates for improving supercapacitor electrodes due to their low cost, large specific pseudocapacitance and facile synthesis methods. Graphene, with its unique two-dimensional structure, shows high electrical conductivity, large specific surface area and outstanding mechanical properties, which makes it an excellent material for lithium ion batteries, fuel cells and supercapacitors. The combination of CPs and graphene as electrode material is expected to boost the properties of supercapacitors. In this review, we summarize recent reports on three different CP/graphene composites as electrode materials for supercapacitors, discussing synthesis and electrochemical performance. Novel flexible and wearable devices based on CP/graphene composites are introduced and discussed, with an eye to recent developments and challenges for future research directions.

Origins and Implications of Interfacial Capacitance Enhancements in C60-Modified Graphene Supercapacitors

Understanding and controlling the electrical response at a complex electrode-electrolyte interface is key to the development of next-generation supercapacitors and other electrochemical devices. In this work, we apply a theoretical framework based on the effective screening medium and reference interaction site model to explore the role of electrical double-layer (EDL) formation and its interplay with quantum capacitance in graphene-based supercapacitors. In addition to pristine graphene, we investigate a novel C₆₀-modified graphene supercapacitor material, which promises higher charge-storage capacity. Beyond the expected enhancement in the quantum capacitance, we find that the introduction of C₆₀ molecules significantly alters the EDL response. These changes in EDL are traced to the interplay between surface morphology and charge localization character and ultimately dominate the overall capacitive improvement in the hybrid system. Our study highlights a complex interplay among surface morphology, electronic structure, and interfacial capacitance, suggesting general improvement strategies for optimizing carbon-based supercapacitor materials.

Self-assembling graphene-anthraquinone-2-sulphonate supramolecular nanostructures with enhanced energy density for supercapacitors

Boosting the energy density of capacitive energy storage devices remains a crucial issue for facilitating applications. Herein, we report a graphene-anthraquinone supramolecular nanostructure by self-assembly for supercapacitors. The sulfonated anthraquinone exhibits high water solubility, a π-conjugated structure and redox active features, which not only serve as a spacer to interact with and stabilize graphene but also introduce extra pseudocapacitance contributions. The formed nest-like three-dimensional (3D) nanostructure with further hydrothermal treatment enhances the accessibility of ion transfer and exposes the redox-active quinone groups in the electrolytes. A fabricated all-solid-state flexible symmetric device delivers a high specific capacitance of 398.5 F g^-1 at 1 A g^-1 (1.5 times higher than graphene), superior energy density (52.24 Wh kg^-1 at about 1 kW kg^-1) and good stability (82% capacitance retention after 10 000 cycles).

Influence of carbon substrate on the electrochemical performance of carbon/manganese oxide hybrids in aqueous and organic electrolytes

The carbon substrate has an important influence on the electrochemical performance of manganese oxide/carbon supercapacitors. Stable performance further requires asymmetric cell design in organic and aqueous electrolytes.