Enhancing the Performance of a Battery-Supercapacitor Hybrid Energy Device Through Narrowing the Capacitance Difference Between Two Electrodes via the Utilization of 2D MOF-Nanosheet-Derived Ni@Nitrogen-Doped-Carbon Core-Shell Rings as Both Negative and Positive Electrodes

MOF-Based Bioelectronic Supercapacitors

Metal-organic frameworks (MOFs) represent a highly promising material class for bioelectronic supercapacitors, characterized by their adjustable structures, extensive surface areas, and superior electrochemical properties. This research explores the synthesis and incorporation of MOF-based materials into bioelectronic devices aimed at energy storage and biosensing applications. The focus is on improving the electrochemical performance of MOFs while preserving their structural integrity through functionalization with biocompatible polymers and conductive materials. The resulting MOF-based bioelectronic supercapacitors exhibit significant improvements in specific capacitance, energy density, and cycling stability. Additionally, the inclusion of bioreceptors allows for the simultaneous detection of biochemical signals alongside energy storage, thus enabling innovative applications in wearable electronics and health monitoring systems. These results suggest that MOF-based supercapacitors have the capacity to fulfill energy storage needs while also advancing bioelectronics by merging energy and sensing capabilities.

Interfacial modulation strategy using poly(3,4-ethylenedioxythiophene)-poly(4-styrenesulfonate) (PEDOT:PSS) and ultrathin two-dimensional metal-organic framework nanosheets for wearable supercapacitors: Solution engineering

Two-dimensional metal-organic frameworks (2D MOFs) hold great promise as electrochemically active materials. However, their application in MOF nanocomposite electrodes in solution engineering is limited by structural self-stacking and imperfect conductive pathways. In this study, we used meso-tetra(4-carboxyphenyl) porphine (TCPP) with off-domain π-bonds to reconstitute Zn-TCPP (ZMOF) and poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) through an interfacial modulation strategy involving electrostatic coupling and hydrogen bonding, creating a conductive composite with a nanosheet structure. The negatively charged PSS and ZMOF formed a three-dimensional interconnected conductive network with excellent interfaces. The positively charged PEDOT, fine tuned with the lamellar structure, established strong π-π stacking interactions between the porphyrin and thiophene rings. ZMOF also induced changes in the PEDOT chain structure, weakening PSS entanglement and enhancing charge-transport properties. The specific capacitance of the prepared supercapacitor was as high as 967.8 F g-1. Flexible supercapacitors produced on a large scale using dispensing printing technology exhibited an energy density of 1.85 μWh cm-2 and a power density of 7.08 μW cm-2. This interfacial modulation strategy also exhibited excellent wearable properties, with 96 % capacitance retention at a 180° bending angle and stable cycling performance. This study presented a significant advancement in the functionalization of 2D materials, highlighting their potential for device-grade capacitive architectures.

Overview of recent developments in carbon-based nanocomposites for supercapacitor applications

Energy storage devices are recognized as environmentally friendly technologies. Supercapacitors, known for their high cycle stability, have been proposed as potential alternatives to fossil fuels. Recent studies have focused on selecting suitable electrode materials to achieve energy storage systems with high stability, high specific capacity, and biocompatibility. In particular, carbon-based electrode materials, such as graphene oxide, activated carbon, carbon nanotubes, and carbon-based quantum dots, have attracted considerable attention due to their intrinsic properties, such as high conductivity and stability. However, carbon materials alone exhibit limitations, such as low energy density and low specific capacitance. To address this limitation, the synergistic effect of carbon materials has been combined with other electroactive materials to develop electrode materials with enhanced supercapacitor properties. The present study also investigates the supercapacitor performance of carbon-based nanocomposites. It examines the effect of each carbon material (AC, CNT, GO, rGO) on improving the performance of other electroactive materials, including metal oxides, metal sulfides, MXenes, MOFs, and conductive polymers. This study provides valuable insights for further studies on carbon-based electrode materials for supercapacitor applications.

Deashing Strategy on Biomass Carbon for Achieving High-Performance Full-Supercapacitor Electrodes

The porous carbon materials, namely, MC700/800, PC700/800, and SC700/800, have been prepared using several biomasses (mushroom dreg, Chinese parasol leaves, and Siraitia grosvenorii leaves) as individual precursors at 700 and 800 °C activation temperatures. Among these carbon-negative electrodes, SC700 exhibits an impressive specific capacitance, nearly 2-fold that of commercial activated carbon (169.5 F g-1). When assembled with a Ni(OH)2 positive electrode in asymmetric supercapacitors, the SC700//Ni(OH)2 device can achieve a specific capacitance of 80 F g-1 and an energy density of 32.16 Wh kg-1 at 1700 W kg-1. In contrast, the MC700 electrode can display inferior performance potentially attributed to the high ash content in the biomass. To further optimize the activated process of the MC700 product, three deashing carbon negative electrodes (denoted as MC(H2O), MC(HF), and MC(Mix)) were prepared by deashing treatment using H2O, HF, and mixed acid, and then a modified composite positive electrode (MC700@MnO2(MCM)) has been prepared by doping with MnO2. Electrochemical testing demonstrates that the deashing strategy achieves a significant capacitance enhancement compared to the primary carbon material while maintaining excellent cyclic stability. The asymmetric supercapacitors, assembled from these decorated electrode materials, exhibited a maximum energy density of 21.08 Wh kg-1 and a power density of 1150 W kg-1 under a high-voltage window of 2.2 V. Additionally, this type of full device can power 28 LEDs for approximately 5 min.

Insight into Electrochemical Performance of Nitrogen-Doped Carbon/NiCo-Alloy Active Nanocomposites

Nanocomposites containing Ni or Co or NiCo alloy and nitrogen-doped carbon with diverse ratios have been prepared and utilized as active elements in supercapacitors. The atomic contents of nitrogen, nickel, and cobalt have been adjusted by the supplement amount of Ni and Co salts. In virtue of the excellent surface groups and rich redox active sites, the NC/NiCo active materials exhibit superior electrochemical charge-storage performances. Among these as-prepared active electrode materials, the NC/NiCo1/1 electrode performs better than other bimetallic/carbon electrodes and pristine metal/carbon electrodes. Several characterization methods, kinetic analyses, and nitrogen-supplement strategies determine the specific reason for this phenomenon. As a result, the better performance can be ascribed to a combination of factors including the high surface area and nitrogen content, proper Co/Ni ratio, and relatively low average pore size. The NC/NiCo electrode delivers a maximum capacity of 300.5 C g^-1 and superior capacity retention of 92.30% after 3000 unceasing charge-discharge cycles. After assembling it into the battery-supercapacitor hybrid device, a high energy density of 26.6 Wh kg^-1 (at 412 W kg^-1 ) is achieved, comparable to the recent reports. Furthermore, this device can also power four light-emitting-diode (LED) demos, suggesting the potential practicability of these N-doped carbon compositing with bimetallic materials.

MOF-derived NiCo-LDH Nanocages on CuO Nanorod Arrays for Robust and High Energy Density Asymmetric Supercapacitors

Layered double hydroxide (LDH) is widely explored in supercapacitors on account of its high capacity, adjustable composition and easy synthesis process. Unfortunately, solitary LDH still has great limitations as an electrode material due to its shortcomings, such as poor conductivity and easy agglomeration. Herein, nanoflakes assembled NiCo-LDH hollow nanocages derived from a metal-organic framework (MOF) precursor are strung by CuO nanorods formed from etching and oxidation of copper foam (CF), forming hierarchical CuO@NiCo-LDH heterostructures. The as-synthesized CuO@NiCo-LDH/CF shows a large capacitance (5607 mF cm^-2 at 1 mA cm^-2 ), superior rate performance (88.3 % retention at 10 mA cm^-2 ) and impressive cycling durability (93.1 % capacitance is retained after 5000 cycles), which is significantly superior to control CuO/CF, CuO@ZIF-67/CF, NiCo-LDH/CF and Cu(OH)₂ @NiCo-LDH/CF electrodes. Besides, an asymmetrical supercapacitor consists of CuO@NiCo-LDH/CF and activated carbon displays a maximum energy density of 47.3 Wh kg^-1 , and its capacitance only declines by 6.8 % after 10000 cycles, demonstrating remarkable cycling durability. The advantages of highly conductive and robust CuO nanorods, MOF-derived hollow structure and the core-shell heterostructure contribute to the outstanding electrochemical performance. This synthesis strategy can be extended to design various core-shell heterostructures adopted in versatile electrochemical energy storage applications.

Effect of Electrolytic Cations on a 3D Cd-MOF for Supercapacitive Electrodes

A cadmium-based metal-organic framework (Cd-MOF) is synthesized in a facile manner at ambient temperature by an easy slow diffusion process. The three-dimensional (3D) structure of Cd-MOF is authenticated by single-crystal X-ray diffraction studies and exhibits a cuboid-shaped morphology with an average edge length of ∼1.13 μm. The prepared Cd-MOF was found to be electroactive in nature, which resulted in a specific capacitance of 647 F g^-1 at 4 A g^-1 by maintaining a retention of ∼78% over 10,000 successive cycles in the absence of any binder. Further, to distinguish the efficiency of Cd-MOF electrodes, different electrolytes (NaOH, KOH, and LiOH) were explored, wherein NaOH revealed a higher capacitive response due to its combined effect of ionic and hydrated ionic radii. To investigate the practical applicability, an asymmetric supercapacitor (ASC) device is fabricated by employing Cd-MOF as the positive electrode and activated carbon (AC) as the negative electrode, enabling it to light a commercial light-emitting diode (LED) bulb (∼1.8 V). The as-fabricated ASC device delivers comparable energy density and power density.

Tremella-like 2D Nickel-Copper Disulfide with Ultrahigh Capacity and Cyclic Retention for Hybrid Supercapacitors

Two-dimensional (2D) disulfides possess unique physical and chemical properties and are widely used in electronic and photoelectric devices. Tuning the composition and optimizing the structure of the disulfides are feasible approaches to designing target sulfides for hybrid supercapacitors. This work synthesizes the tremella-like nanosheet-connected (Cu_xNi_1-x)S₂ via solvothermal and sulfur-vapor vulcanization. The 2D (Cu_xNi_1-x)S₂ electrode performs a high reversible capacity (526.0 mA h g^-1 at 1 A g^-1), decent capacity retention (75.6%) at 10 A g^-1, and prolonged cyclic retention (94.4% over 15,000 cycles), which is higher than that of (Cu_xNi_1-x)O and monometallic sulfides of NiS₂ and CuS. The elevated electrochemical properties of (Cu_xNi_1-x)S₂ are attributed to the optimized composition with increased redox reaction, enlarged lattice distance, abundant active sites, and attractive electronic and ionic conductivity. Also, (Cu_xNi_1-x)S₂ and active carbon (AC) are assembled to form a hybrid supercapacitor (HSC). The (Cu_xNi_1-x)S₂//AC HSC demonstrates a maximum specific capacitance of 231.0 F g^-1 at 1 A g^-1 and a high energy density of 82.4 W h kg^-1 at a power density of 1.82 kW kg^-1. Outstanding cyclic retentions of 94.9 and 84.5% after 8000 and 10,000 cycles are also obtained. In conclusion, this result suggests a facile routine for preparing a novel 2D layer material of (Cu_xNi_1-x)S₂ with outstanding specific capacity and cycling performance for hybrid supercapacitors.

Stereolithography-Derived Three-Dimensional Pyrolytic Carbon/Mn3O4 Nanostructures for Free-Standing Hybrid Supercapacitor Electrodes

The development of permeable three-dimensional (3D) macroporous carbon architectures loaded with active pseudocapacitive nanomaterials offers hybrid supercapacitor (SC) materials with higher energy density, shortened diffusion length for ions, and higher charge-discharge rate capability and thereby is highly relevant for electrical energy storage (EES). Herein, structurally complex and tailorable 3D pyrolytic carbon/Mn₃O₄ hybrid SC electrode materials are synthesized through the self-assembly of MnO₂ nanoflakes and nanoflowers onto the surface of stereolithography 3D-printed architectures via a facile wet chemical deposition route, followed by a single thermal treatment. Thermal annealing of the MnO₂ nanostructures concurrent with carbonization of the polymer precursor leads to the formation of a 3D hybrid SC electrode material with unique structural integrity and uniformity. The microstructural and chemical characterization of the hybrid electrode reveals the predominant formation of crystalline hausmannite-Mn₃O₄ after the pyrolysis/annealing process, which is a favorable pseudocapacitive material for EES. With the combination of the 3D free-standing carbon architecture and self-assembled binder-free Mn₃O₄ nanostructures, electrochemical capacitive charge storage with very good rate capability, gravimetric and areal capacitances (186 F g^-1 and 968 mF cm^-2, respectively), and a long lifespan (>92% after 5000 cycles) is demonstrated. It is worth noting that the gravimetric capacitance value is obtained by considering the full mass of the electrode including the carbon current collector. When only the mass of the pseudocapacitive nanomaterial is considered, a capacitance value of 457 F g^-1 is achieved, which is comparable to state-of-the-art Mn₃O₄-based SC electrode materials.

Regulating Ni3+ contents by a cobalt doping strategy in ternary NixCo3−xAl1-LDH nanoflowers for high-performance charge storage

The Ni1Co2Al1-LDH electrode prepared by hydrothermal method delivers a high specific capacitance (728 C g−1 at 1 A g−1) and excellent capacitance retention (93.18% of initial capacitance at 30 A g−1 after 10 000 cycles).

Dual-ligand strategies to assemble S, N-containing metal organic framework nanoflowers for hybrid supercapacitors

Ni-MOF [Ni(Tdc)(Bpy)]n was successfully prepared, and the Ni-MOF//AC hybrid supercapacitor exhibited superior energy density and cycling stability.

Cu/CuxO@C nanocomposites as efficient electrodes for high-performance supercapacitor devices

A novel method, reduction followed by oxidation procedure, has been developed to fabricate the efficient electrodes derivated from metal-organic frameworks (MOFs), which were synthesized using terephthalic acid (TP) or 1,3,5-benzenetricarboxylic...

State of the art developments and prospects of metal-organic frameworks for energy applications

The progress on technologies for the cleaner and ecological transformation and storage of energy to combat effluence or pollution and the impending energy dilemma has recently attracted interest from energy research groups, particularly in the field of coordination chemistry, among inorganic chemists. Carriers for storing energy or facilitating mass and e^- transport are considered significant for energy conversion. Accordingly, considering their properties such as large surface area, low cost, customizable pore diameter, tunable topologies, low densities, and variable frameworks, MOFs (metal-organic frameworks) and their derivatives are well-suited for this purpose. MOFs are an innovative category of porous and crystalline materials, which have gained significant interest in recent years. Thus, herein, we highlight the state of the art progress on MOFs for energy-based applications, as perfect compounds and elements in compound assemblies for converting solar energy, lithium-ion arrays, fuel devices, hydrogen production, photocatalytic CO₂ reduction, proton conduction, etc. In addition, the substantial progress achieved in the production of various composites and derivatives containing MOFs with particular focus on supercapacitors and gas adsorption and storage is summarized, concentrating on the correlation between their coordination structural frameworks and applications in the field of energy. The current improved strategies, challenges, and future prospects are also presented in view of the coordination chemistry governing the structural modification of MOFs for energy applications.

Nitrogen-Doped Carbon Encapsulated Partial Zinc Stannate Nanocomposite for High-Performance Energy Storage Materials

As a bimetal oxide, partial zinc stannate (ZnSnO3) is one of the most promising next-generation lithium anode materials, which has the advantages of low operating voltage, large theoretical capacity (1,317 mA h g-1), and low cost. However, the shortcomings of large volume expansion and poor electrical conductivity hinder its practical application. The core-shell ZnSnO3@ nitrogen-doped carbon (ZSO@NC) nanocomposite was successfully obtained by coating ZnSnO3 with polypyrrole (PPy) through in situ polymerization under ice-bath conditions. Benefiting from this unique compact structure, the shell formed by PPy cannot only effectively alleviate the volume expansion effect of ZnSnO3 but also enhance the electrical conductivity, thus, greatly improving the lithium storage performance. ZSO@NC can deliver a reversible capacity of 967 mA h g-1 at 0.1 A g-1 after 300 cycles and 365 mA h g-1 at 2 A g-1 after 1,000 cycles. This work may provide a new avenue for the synthesis of bimetal oxide with a core-shell structure for high-performance energy storage materials.