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The research focuses on enhancing the energy storage capabilities of mesoporous silica (MCM-41) for supercapacitor applications. Electrodes made solely from MCM-41 do not possess the desired energy density required for electronic devices. To address this, combining ferrites with MCM-41 has been proposed as a means to enhance the electrochemical behavior. In this study, various contents of COF were loaded on MCM-41. Different characterization methods were used to study the physical and surface properties of the as synthesized materials like XRD, FTIR, SEM, TEM, EDX and SEM-mapping. TEM images confirmed that all the as-synthesized composites retained the mesoporous structure, and the particle size of ferrites ranged from 8 to 14 nm. The cyclic voltammetry (CV) and galvanostatic charge–discharge (GCD) techniques were employed to investigate the electrochemical characteristics of the composite materials in H2SO4 electrolyte solution (1.0 M) and a potential window ranging from 0.0 to 0.8 V. The results demonstrated that the incorporation of ferrites onto MCM-41 led to an elevation in specific capacitance, with the highest value (746 F.g−1) observed at 35 COF-MCM-41 composite. However, further increasing the content of ferrites resulted in a decrease in specific capacitance. Furthermore, the prepared composites exhibited excellent cycling stability even after 5000 cycles, with MCM-41, COF, and 35 COF-MCM-41 retaining 84.4%, 89.4%, and 94.8% of their initial specific capacitance, respectively. These findings highlight the significant role played by the dispersion of cobalt ferrite nanoparticles in enhancing pseudocapacitance behavior, thus improving the overall electrochemical performance of the composites. [ABSTRACT FROM AUTHOR]

Layered double hydroxides (LDH) are regarded as attractive pseudocapacitive materials due to their impressive capacitive qualities that may be adjustable to their morphological features. However, the layered structure of LDH renders them susceptible to structural aggregation, which inhibits effective electrolyte transport and limits their practical applicability after limited exposure to active areas. Herein, we propose a simple template-free strategy to synthesize hierarchical hollow sphere NiMn-LDH material with high surface area and exposed active as anode material for supercapacitor application. The template-free approach enables the natural nucleation of Ni-Mn ions resulting in thin sheets that self-assemble into a hollow sphere, offering expended interlayer spaces and abundant redox-active active sites. The optimal NiMn-LDH-12 achieved a specific capacitance of 1010.4 F g−1 at a current density of 0.2 A g−1 with capacitance retention of 70% at 5 A g−1 after 5000 cycles with lower charge transfer impedance. When configured into an asymmetric supercapacitors (ASC) device as NiMn-LDH//AC, the material realized a specific capacitance of 192.4 F g−1 at a current density of 0.2 A g−1 with a good energy density of 47.9 Wh kg−1 and a power density of 196.8 W kg−1. The proposed morphological-tuning route is promising for designing template-free NiMn-LDHs spheres with practical pseudocapacitive characteristics. [ABSTRACT FROM AUTHOR]

The development of hydrogel electrolytes plays a critical role in high-performance flexible supercapacitor devices. Herein, a composite hydrogel electrolyte of polyacrylic acid (PAA) and graphene oxide (GO) has been successfully prepared, where the oxygen-containing functional groups of GO may crosslink and form hydrogen bonds with carboxyl on the molecular chain of PAA, thereby significantly enhancing the mechanical properties of a PAA-based gel electrolyte. The tensile strength increases from 4.0 MPa for pristine PAA gel to 6.1 MPa for PAA/GO composite gel, with the elongation at break rising from 1556% to 1950%. Meanwhile, GO promotes the transportation of electrolyte ions, which are favorable for enhancing the ionic conductivity of the PAA hydrogel. As a result, the assembled supercapacitor based on PAA/GO composite hydrogel electrolyte shows enhanced capacitance retention of 64.3% at a large current density of 20 A g−1 and excellent cycling stability over 10,000 cycles at 5 A g−1. Furthermore, the fabricated flexible supercapacitor devices could maintain outstanding electrochemical performance at various bending angles of 0–90°, indicating a promising prospect for the PAA/GO hydrogel electrolyte in flexible wearable fields. [ABSTRACT FROM AUTHOR]

2D MXenes have emerged as promising supercapacitor electrode materials due to their metallic conductivity, pseudo‐capacitive mechanism, and high density. However, layer‐restacking is a bottleneck that restrains their ionic kinetics and active site exposure. Herein, a carbon dots‐intercalated strategy is proposed to fabricate flexible MXene film electrodes with both large ion‐accessible active surfaces and high density through gelation of calcium alginate (CA) within the MXene nanosheets followed by carbonization. The formation of CA hydrogel within the MXene nanosheets accompanied by evaporative drying endow the MXene/CA film with high density. In the carbonization process, the CA‐derived carbon dots can intercalate into the MXene nanosheets, increasing the interlayer spacing and promoting the electrolytic diffusion inside the MXene film. Consequently, the carbon dots‐intercalated MXene films exhibit high volumetric capacitance (1244.6 F cm−3 at 1 A g−1), superior rate capability (662.5 F cm−3 at 1000 A g−1), and excellent cycling stability (93.5% capacitance retention after 30 000 cycles) in 3 m H2SO4. Additionally, an all‐solid‐state symmetric supercapacitor based on the carbon dots‐intercalated MXene film achieves a high volumetric energy density of 27.2 Wh L−1. This study provides a simple yet efficient strategy to construct high‐volumetric performance MXene film electrodes for advanced supercapacitors. [ABSTRACT FROM AUTHOR]

Summary: Energy storage devices (ESD) are getting significant attention regarding their ability to reduce fossil fuel usage. Batteries and electrochemical supercapacitors are two well‐known ESDs with supercapacitors preferred for their high energy discharge potential. The metal oxides (MOs) with robust redox characteristics are ideal candidates for supercapacitors, although their capacitance still lacks behind the theoretical values. Here, partial reduced or oxygen‐deficient MOs have been identified have proven promising to reach the desired capacitance. The introduction of oxygen vacancies into MOs can effectively enhance their electrochemical properties without altering the inherent characteristics of MOs. This review discusses the recent progress on new oxygen‐deficient MOs and their performance as a supercapacitor. The importance of oxygen vacancy is described, followed by the traditional synthesis route to producing MOs. The present pathways for generating oxygen vacancies and their analytical assessment are covered in‐depth, followed by a section on the most advanced analytical techniques for detecting and interpreting the creation of such vacancies. The influence of oxygen vacancies on the supercapacitive performance of the most researched MOs is provided with the challenges and prospects of oxygen‐deficient MOs in supercapacitor application. [ABSTRACT FROM AUTHOR]

A plate-like Bi/Bi 2 O 3 -C heterostructure with boosted potassium storage performances is designed through a MOF-derived structure-inheritance strategy, where the Bi and Bi 2 O 3 can form hetero-particles that are uniformly embedded within the MOF-derived carbon skeleton. [Display omitted] Bismuth-based materials are regarded as promising anode materials for potassium ion batteries (PIBs) due to their high theoretical capacity and low working potential. However, the large volume expansion and sluggish kinetics during cycling are major limitations to their practical application. Herein, a unique Bi/Bi 2 O 3 -C heterostructure was designed through a simple Bi-metal–organic framework (MOF) modulation-pyrolysis process. X-ray photoelectron spectroscopy, transmission electron microscopy, and X-ray diffraction revealed that the Bi and Bi 2 O 3 can form hetero-particles, which were uniformly embedded in a plate-like carbon skeleton, constructing a Bi/Bi 2 O 3 -C heterostructure. The carbon skeleton and the formation of numerous hetero-interfaces between Bi, Bi 2 O 3 , and carbon can effectively promote the interfacial charge transfer, shorten the K+ diffusion pathway, and alleviate the volume expansion of Bi/Bi 2 O 3 during potassiation. Consequently, the Bi/Bi 2 O 3 -C heterostructure exhibited a high reversible capacity of 426.0 mAh g−1 at 50 mA g−1, excellent cycle performance of 251.8 mAh g−1 after 350 cycles with a capacity retention of 76.6 %, and superior rate capability of 82.7 mAh g−1 at 1 A g−1, demonstrating its promising potential for the application of PIBs anode. [ABSTRACT FROM AUTHOR]