Chlorine-Induced In Situ Regulation to Synthesize Graphene Frameworks with Large Specific Area for Excellent Supercapacitor Performance

Iodine intercalation-assisted alkali activation constructs coal-based porous carbon for high-performance supercapacitors

Supercapacitors have the advantages of fast charging and discharging speeds, high power density, long cycle life, and wide operating temperature range. They are widely used in portable electronic equipment, rail transit, industry, military, aerospace, and other fields. The design and preparation of low-cost, high-performance electrode materials still pose a bottleneck that hinders the development of supercapacitors. In this paper, coal was used as the raw material, and the coal-based porous carbon electrode material was constructed using the iodine intercalation-assisted activation method and used for supercapacitors. The CK-700 electrode exhibits excellent charge storage performance in a 6 M potassium hydroxide (KOH) electrolyte, with a maximum specific capacitance of 350 F/g at a current density of 0.5 A/g. In addition, it has an excellent rate performance (310 F/g at 1 A/g) and cycle stability (capacitance retention up to 91.7 % after 30000 cycles). This work provides a method for realizing high-quality, high-yield and low-cost preparation of coal-based porous carbon, and an idea for improving the performance of supercapacitors.

Surface Engineering of Anodic WO3 Layers by In Situ Doping for Light-Assisted Water Splitting

This study presents a novel approach to fabricating anodic Co-F-WO3 layers via a single-step electrochemical synthesis, utilizing cobalt fluoride as a dopant source in the electrolyte. The proposed in situ doping technique capitalizes on the high electronegativity of fluorine, ensuring the stability of CoF2 throughout the synthesis process. The nanoporous layer formation, resulting from anodic oxide dissolution in the presence of fluoride ions, is expected to facilitate the effective incorporation of cobalt compounds into the film. The research explores the impact of dopant concentration in the electrolyte, conducting a comprehensive characterization of the resulting materials, including morphology, composition, optical, electrochemical, and photoelectrochemical properties. The successful doping of WO3 was confirmed by energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Raman spectroscopy, photoluminescence measurements, X-ray photoelectron spectroscopy (XPS), and Mott-Schottky analysis. Optical studies reveal lower absorption in Co-doped materials, with a slight shift in band gap energies. Photoelectrochemical (PEC) analysis demonstrates improved PEC activity for Co-doped layers, with the observed shift in photocurrent onset potential attributed to both cobalt and fluoride ions catalytic effects. The study includes an in-depth discussion of the observed phenomena and their implications for applications in solar water splitting, emphasizing the potential of the anodic Co-F-WO3 layers as efficient photoelectrodes. In addition, the research presents a comprehensive exploration of the electrochemical synthesis and characterization of anodic Co-F-WO3, emphasizing their photocatalytic properties for the oxygen evolution reaction (OER). It was found that Co-doped WO3 materials exhibited higher PEC activity, with a maximum 5-fold enhancement compared to pristine materials. Furthermore, the studies demonstrated that these photoanodes can be effectively reused for PEC water-splitting experiments.

3D Continuously Porous Graphene for Energy Applications

Constructing bulk graphene materials with well-reserved 2D properties is essential for device and engineering applications of atomically thick graphene. In this article, the recent progress in the fabrications and applications of sterically continuous porous graphene with designable microstructures, chemistries, and properties for energy storage and conversion are reviewed. Both template-based and template-free methods have been developed to synthesize the 3D continuously porous graphene, which typically has the microstructure reminiscent of pseudo-periodic minimal surfaces. The 3D graphene can well preserve the properties of 2D graphene of being highly conductive, surface abundant, and mechanically robust, together with unique 2D electronic behaviors. Additionally, the bicontinuous porosity and large curvature offer new functionalities, such as rapid mass transport, ample open space, mechanical flexibility, and tunable electric/thermal conductivity. Particularly, the 3D curvature provides a new degree of freedom for tailoring the catalysis and transport properties of graphene. The 3D graphene with those extraordinary properties has shown great promises for a wide range of applications, especially for energy conversion and storage. This article overviews the recent advances made in addressing the challenges of developing 3D continuously porous graphene, the benefits and opportunities of the new materials for energy-related applications, and the remaining challenges that warrant future study.

More Sustainable Chemical Activation Strategies for the Production of Porous Carbons

The preparation of porous carbons attracts a great deal of attention given the importance of these materials in many emerging applications, such as hydrogen storage, CO₂ capture, and energy storage in supercapacitors and batteries. In particular, porous carbons produced by applying chemical activation methods are preferred because of the high pore development achieved. However, given the environmental risks associated with conventional activating agents such as KOH, the development of greener chemical activation methodologies is an important objective. This Review summarizes recent progress in the production of porous carbons by using more sustainable strategies based on chemical activation. The use of less-corrosive chemical agents as an alternative to KOH is thoroughly reviewed. In addition, progress achieved to date by using emerging self-activation methodologies applied to organic salts and biomass products is also discussed.

3D Graphene Materials: From Understanding to Design and Synthesis Control

Carbon materials, with their diverse allotropes, have played significant roles in our daily life and the development of material science. Following 0D C₆₀ and 1D carbon nanotube, 2D graphene materials, with their distinctively fascinating properties, have been receiving tremendous attention since 2004. To fulfill the efficient utilization of 2D graphene sheets in applications such as energy storage and conversion, electrochemical catalysis, and environmental remediation, 3D structures constructed by graphene sheets have been attempted over the past decade, giving birth to a new generation of graphene materials called 3D graphene materials. This review starts with the definition, classifications, brief history, and basic synthesis chemistries of 3D graphene materials. Then a critical discussion on the design considerations of 3D graphene materials for diverse applications is provided. Subsequently, after emphasizing the importance of normalized property characterization for the 3D structures, approaches for 3D graphene material synthesis from three major types of carbon sources (GO, hydrocarbons and inorganic carbon compounds) based on GO chemistry, hydrocarbon chemistry, and new alkali-metal chemistry, respectively, are comprehensively reviewed with a focus on their synthesis mechanisms, controllable aspects, and scalability. At last, current challenges and future perspectives for the development of 3D graphene materials are addressed.

Stable, Dual Redox Unit Organic Electrodes

The development of organic materials for electrochemical energy storage has attracted great attention because of their high natural abundance and relatively low toxicity. The bulk of these studies focus on small molecules, polymers, or porous/framework-type materials that employ one type of redox moiety. Here, we report the synthesis and testing of organic materials that incorporate two distinct types of redox units: triptycene-based quinones and perylene diimides. We examine this "dual redox" concept through the synthesis of both frameworks and small molecule model compounds with the redox units positioned at the vertices and connection points. Such a design increases the theoretical capacity of the material. It also imparts high stability because both examples are relatively rigid and highly insoluble in the electrolyte. Lithium-ion batteries consisting of the framework and the small molecule have an excellent cycling retention of 75 and 77%, respectively, over 500 cycles at 1 C. Our work emphasizes the advantages of using multiple redox units in the design of the cathodic materials and redox-active triptycene linkages to achieve high cycling stability.

Thermally reduced fluorographenes as efficient electrode materials for supercapacitors

There is an urgent need for a simple and up-scalable method for the preparation of supercapacitor electrode materials due to increasing global energy consumption worldwide. We have discovered that fluorographene exhibits great potential for the development of new kinds of supercapacitors aimed at practical applications. We have shown that time control of isothermal reduction of fluorographite at 450 °C under a hydrogen atmosphere led to the fine-tuning of fluorine content and electronic properties of the resulting fluorographene derivatives. Charge transfer resistances (R_ct) of the thermally reduced fluorographenes (TRFGs) were decreased with respect to the pristine fluorographene; however, the R_ctvs. time-of-reduction plot showed a v-shaped profile. The specific capacitance vs. time-of-reduction of TRFG followed the v-shaped trend, which could be the result of the decreasing content of sp³ carbons and increasing content of structural defects. An optimized material exhibited values of specific capacitance up to 539 F g^-1 recorded at a current density of 0.25 A g^-1 and excellent cycling durability with 100% specific capacitance retention after 1500 cycles in a three-electrode configuration and 96.7% of specific capacitance after 30 000 cycles in a two-electrode setup.

Three-Dimensional Arylene Diimide Frameworks for Highly Stable Lithium Ion Batteries

Lithium ion batteries are the best commercial technology to satisfy the energy storage needs of current and emerging applications. However, the use of transition-metal-based cathodes precludes them from being low-cost, sustainable, and environmentally benign, even with recycling programs in place. In this study, we report a highly stable organic material that can be used in place of the transition-metal cathodes. By creating a three-dimensional framework based on triptycene and perylene diimide (PDI), a cathode can be constructed that mitigates stability issues that organic electrodes typically suffer from. When a lithium ion battery is assembled using the PDI-triptycene framework (PDI-Tc) cathode, a capacity of 75.9 mAh g^-1 (78.7% of the theoretical value) is obtained. Importantly, the battery retains a near perfect Coulombic efficiency and >80% of its capacity after cycling 500 times, which is the best value reported to date for PDI-based materials.

Effects of Nanoporous Carbon Derived from Microalgae and Its CoO Composite on Capacitance

Nanoporous carbon was synthesized from microalgae as a promising electrode material for electric double layer capacitors due to its large specific surface area and controllable pore structures. The pore textural properties of the algae-derived-carbon (ADC) samples were measured by N₂ adsorption and desorption at 77 K. The performance of the activated carbon (AC) as supercapacitor electrodes was determined by the cyclic voltammetry and galvanostatic charge/discharge tests. The effect of the nanoporous carbon structure on capacitance was demonstrated by calculating the contributions of micropores and mesopores toward capacitance. Capacitance was significantly affected by both pore size and pore depth. To further increase the specific capacity, a single-pot synthesis of porous carbon supported CoO composite (CoO/ADC) electrode material was developed using microalgae as the carbon source and Co(OH)₂ as both a carbon activation agent and CoO precursor. After carbonization, CoO particles were formed and embedded in the ADC matrix. The synergic contributions from the combined CoO and ADC resulted in better supercapacitor performance as compared to that of the pure CoO electrode. The calculated specific capacities of CoO/ADC were 387 and 189 C g^-1 at 0.2 and 5 A g^-1, respectively, which were far more than the capacities of pure CoO electrode (185 C g^-1 at 0.2 A g^-1 and 77 C g^-1 at 5 A g^-1). The cycle stability of CoO/ADC also increased significantly (83% retention of the initial capacity for CoO/ADC vs 63% for pure CoO). This research had developed a viable and promising solution for producing composite electrodes in a large quantity for commercial application.

Functionalization of BaTiO3 nanoparticles with electron insulating and conducting organophosphazene-based hybrid materials

Structuring of core–shell dielectric nanoparticles.

Supramolecule-Inspired Fabrication of Carbon Nanoparticles In Situ Anchored Graphene Nanosheets Material for High-Performance Supercapacitors

The remarkable electrochemical performance of graphene-based materials has drawn a tremendous amount of attention for their application in supercapacitors. Inspired by supramolecular chemistry, the supramolecular hydrogel is prepared by linking β-cyclodextrin to graphene oxide (GO). The carbon nanoparticles-anchored graphene nanosheets are then assembled after the hydrothermal reduction and carbonization of the supramolecular hydrogels; here, the β-cyclodextrin is carbonized to carbon nanoparticles that are uniformly anchored on the graphene nanosheets. Transmission electron microscopy reveals that carbon nanoparticles with several nanometers are uniformly anchored on both sides of graphene nanosheets, and X-ray diffraction spectra demonstrate that the interlayer spacing of graphene is enlarged due to the anchored nanoparticles among the graphene nanosheets. The as-prepared carbon nanoparticles-anchored graphene nanosheets material (C/r-GO-1:3) possesses a high specific capacitance (310.8 F g^-1, 0.5 A g^-1), superior rate capability (242.5 F g^-1, 10 A g^-1), and excellent cycle stability (almost 100% after 10 000 cycles, at the scan rate of 50 mV s^-1). The outstanding electrochemical performance of the resulting C/r-GO-1:3 is mainly attributed to (i) the presence of the carbon nanoparticles, (ii) the enlarged interlayer spacing of the graphene sheets, and (iii) the accelerated ion transport rates toward the interior of the electrode material. The supramolecule-inspired approach for the synthesis of high-performance carbon nanoparticles-modified graphene sheets material is promising for future application in graphene-based energy storage devices.