Electrochemical performance of composites made of rGO with Zn-MOF and PANI as electrodes for supercapacitors

Engineering the structures of ZnCo-MOFs via a ligand effect for enhanced supercapacitor performance

Tuning the structures, compositions and morphologies of metal-organic frameworks (MOFs) is critical to boosting their supercapacitor performances. In this study, a ligand-engineering strategy was adopted to fabricate ZnCo-bimetallic MOFs with unique properties using three different ligands (2-methylimidazole, terephthalic acid and 2-amino terephthalic acid) under the same synthesis protocol. The variation in the electron-donating ability of the three ligands gave rise to changes in their structural, morphological and electrochemical properties. Compared to other MOFs, the imidazole-based ZnCo-MOF (ZnCo-MOF-HMIM) with a dodecahedron morphology, good specific surface area and moderate pore characteristics provided considerable electron transport paths for ion migration on the electrode surface site, which guarantees a greater charge storage. Specifically, ZnCo-MOF-HMIM delivered the best specific capacity of 176.8 m h A g-1 at 1 A g-1 specific current and retains about 87.5% of its capacity at 10 A g-1 after 5000 cycles. Furthermore, the asymmetric device achieved a specific energy of 28.2 W h kg-1 at a specific power of 1025.4 W kg-1 and demonstrates remarkable coulombic efficiency and capacity retention of 98.4% and 80.0% at 10 A g-1 over 10 000 cycles respectively. The presence of an N donor atom in the imidazole ligand which imparts high hydrophobicity, and the synergistic effects of Zn and Co ions could predispose ZnCo-MOF-HMIM to have more active sites and greater stability for enhanced performance. This work provides insight into the key role of ligands in the formation mechanism of bimetallic MOFs for enhanced electrochemical energy storage.

A composite of pineapple leaf-derived porous carbon integrated with ZnCo-MOF for high-performance supercapacitors

Electrochemical energy storage heavily depends on the activity and stability of electrode materials. However, the direct use of metal-organic frameworks (MOFs) as supercapacitor electrode materials poses challenges due to their low electrical conductivity. In this study, pineapple leaf-derived biochar (PLB) was employed as a carrier for bimetallic ZnCo-MOF, resulting in the composite ZnCo-MOF@PLB-800, synthesized through in situ growth and pyrolysis at 800 °C. The highly porous structure of PLB alleviated the aggregation of ZnCo-MOF particles, thereby enhancing the electron transfer rate and improving the conductivity of the electrode material. Electrochemical testing revealed that ZnCo-MOF@PLB-800 achieved a specific capacitance of 698.5 F g-1 at a current density of 1 A g-1. The assembled asymmetric supercapacitor (ASC) demonstrated excellent specific capacitance and electrochemical stability, delivering a high energy density of 35.85 W h kg-1 at a power density of 350 W kg-1, with robust cycle stability, retaining 90.4% capacitance after 8000 cycles. This work offers an effective integration of bimetallic MOFs with waste biomass-derived porous carbon for electrode materials, supporting both energy storage applications and environmental sustainability.

Metal ion and organic ligand disubstituted bimetallic metal-organic framework nanosheets for high-performance alkaline zinc-based batteries

Herein, a disubstitution strategy of metal ions and organic ligands is employed to synthesize metal-organic framework (MOF) nanosheets with a three-dimensional (3D) porous structure and a highly active metal-sulfur (M-S, M = Co and Ni) region. The obtained MOFs//Zn batteries exhibit excellent electrochemical properties and the electrochemical reaction mechanism was elucidated through a series of ex situ characterizations.

Metal-Organic Frameworks and Their Derivatives-Based Nanostructure with Different Dimensionalities for Supercapacitors

With the urgent demand for the achievement of carbon neutrality, novel nanomaterials, and environmentally friendly nanotechnologies are constantly being explored and continue to drive the sustainable development of energy storage and conversion installations. Among various candidate materials, metal-organic frameworks (MOFs) and their derivatives with unique nanostructures have attracted increasing attention and intensive investigation for the construction of next generation electrode materials, benefitting from their unique intrinsic characteristics such as large specific surface area, high porosity, and chemical tunability as well as the interconnected channels. Nevertheless, the poor electrochemical conductivity severely limits their application prospects, hence a variety of nanocomposites with multifarious structures have been designed and proposed from different dimensionalities. In this review, recent advances based on MOFs and their derivatives in different dimensionalities ranging from 1D nanopowders to 2D nanofilms and 3D aerogels, as well as 4D self-supporting electrodes for supercapacitors are summarized and highlighted. Furthermore, the key challenges and perspectives of MOFs and their derivatives-based materials for the practical and sustainable electrochemical energy conversion and storage applications are also briefly discussed, which may be served as a guideline for the design of next-generation electrode materials from different dimensionalities.

Advances of Electroactive Metal-Organic Frameworks

The preparation of electroactive metal-organic frameworks (MOFs) for applications of supercapacitors and batteries has received much attention and remarkable progress during the past few years. MOF-based materials including pristine MOFs, hybrid MOFs or MOF composites, and MOF derivatives are well designed by a combination of organic linkers (e.g., carboxylic acids, conjugated aromatic phenols/thiols, conjugated aromatic amines, and N-heterocyclic donors) and metal salts to construct predictable structures with appropriate properties. This review will focus on construction strategies of pristine MOFs and hybrid MOFs as anodes, cathodes, separators, and electrolytes in supercapacitors and batteries. Descriptions and discussions follow categories of electrochemical double-layer capacitors (EDLCs), pseudocapacitors (PSCs), and hybrid supercapacitors (HSCs) for supercapacitors. In contrast, Li-ion batteries (LIBs), Lithium-sulfur batteries (LSBs), Lithium-oxygen batteries (LOBs), Sodium-ion batteries (SIBs), Sodium-sulfur batteries (SSBs), Zinc-ion batteries (ZIBs), Zinc-air batteries (ZABs), Aluminum-sulfur batteries (ASBs), and others (e.g., LiSe, NiZn, H⁺ , alkaline, organic, and redox flow batteries) are categorized for batteries.

In Situ Synthesis of Ni-BTC Metal-Organic Framework@Graphene Oxide Composites for High-Performance Supercapacitor Electrodes

In response to serious ecological and environmental problems worldwide, a novel graphene oxide (GO) induction method for the in situ synthesis of GO/metal organic framework (MOF) composites (Ni-BTC@GO) for supercapacitors with excellent performance is presented in this study. For the synthesis of the composites, 1,3,5-benzenetricarboxylic acid (BTC) is used as an organic ligand due to its economic advantages. The optimum amount of GO is determined by a comprehensive analysis of morphological characteristics and electrochemical tests. 3D Ni-BTC@GO composites show a similar spatial structure to that of Ni-BTC, revealing that Ni-BTC could provide an effective framework and avoid GO aggregation. The Ni-BTC@GO composites have a more stable electrolyte-electrode interface and an improved electron transfer route than pristine GO and Ni-BTC. The synergistic effects of GO dispersion and Ni-BTC framework on electrochemical behavior are determined, where Ni-BTC@GO 2 achieves the best performance in energy storage performance. Based on the results, the maximum specific capacitance is 1199 F/g at 1 A/g. Ni-BTC@GO 2 has an excellent cycling stability of 84.47% after 5000 cycles at 10 A/g. Moreover, the assembled asymmetric capacitor exhibits an energy density of 40.89 Wh/kg at 800 W/kg, and it still remains at 24.44 Wh/kg at 7998 W/kg. This material is expected to contribute to the design of excellent GO-based supercapacitor electrodes.

Recent Progress of Advanced Conductive Metal-Organic Frameworks: Precise Synthesis, Electrochemical Energy Storage Applications, and Future Challenges

Metal-organic frameworks (MOFs) with diverse composition, tunable structure, and unique physicochemical properties have emerged as promising materials in various fields. The tunable pore structure, abundant active sites, and ultrahigh specific surface area can facilitate mass transport and provide outstanding capacity, making MOFs an ideal active material for electrochemical energy storage and conversion. However, the poor electrical conductivity of pristine MOFs severely limits their applications in electrochemistry. Developing conductive MOFs has proved to be an effective solution to this problem. This review focuses on the design and synthesis of conductive MOF composites with judiciously chosen conducting materials, pristine MOFs, and assembly methods, as well as the preparation of intrinsically conductive MOFs based on building 2D π-conjugated structures, introducing mixed-valence metal ions/redox-active ligands, designing π-π stacked pathways, and constructing infinite metal-sulfur chains (-M-S-)_∞ . Furthermore, recent progress and challenges of conductive MOFs for energy storage and conversion (supercapacitors, Li-ion batteries, Li-S batteries, and electrochemical water splitting) are summarized.

Evaluation of the Synergistic Effect of Graphene Oxide Sheets and Co3O4 Wrapped with Vertically Aligned Arrays of Poly (Aniline-Co-Melamine) Nanofibers for Energy Storage Applications

In the present study, Co3O4 and graphene oxide (GO) are used as reinforcement materials in a copolymer matrix of poly(aniline-co-melamine) to synthesize ternary composites. The nanocomposite was prepared by oxidative in-situ polymerization and used as an electrode material for energy storage. The SEM images revealed the vertically aligned arrays of copolymer nanofibers, which entirely wrapped the GO sheets and Co3O4 nanoparticles. The EDX and mapping analysis confirmed the elemental composition and uniform distribution in the composite. The XRD patterns unveiled composites' phase purity and crystallinity through characteristic peaks appearing at their respective 2θ values in the XRD spectrum. The FTIR spectrums endorse the successful synthesis of composites, whereas TGA analysis revealed the higher thermal stability of composites. The cyclic voltammetry, galvanostatic charge-discharge, and electrochemical impedance spectroscopy are employed to elucidate the electrochemical features of electrodes. The ternary composite PMCoG-2 displayed the highest specific capacity of 134.36 C/g with 6 phr of GO, whereas PMCoG-1 and PMCoG-3 exhibited the specific capacities of 100.63 and 118.4 C/g having 3 phr and 12 phr GO at a scan rate of 0.003 V/s, respectively. The best electrochemical performance of PMCoG-2 is credited to the synergistic effect of constituents of the composite material.

Banana Peel and Conductive Polymers-Based Flexible Supercapacitors for Energy Harvesting and Storage

Flexible supercapacitors are highly demanding due to their wearability, washability, lightweight property and rollability. In this paper, a comprehensive review on flexible supercapacitors based on conductive polymers such as polypyrrole (PPy), polyaniline (PANI) and poly(3,4-ethylenedioxtthiophne)-polystyrene sulfonate (PEDOT:PSS). Methods of enhancing the conductivity of PEDOT:PSS polymer using various composites and chemical solutions have been reviewed in detail. Furthermore, supercapacitors based on carbonized banana peels and methods of activation have been discussed in point. This review covers the up-to-date progress achieved in conductive polymer-based materials for supercapacitor electrodes. The effect of various composites with PEDOT:PSS have been discussed. The review result indicated that flexible, stretchable, lightweight, washable, and disposable wearable electronics based on banana peel and conductive polymers are highly demanding.

A Self-Standing Binder-Free Biomimetic Cathode Based on LMO/CNT Enhanced with Graphene and PANI for Aqueous Rechargeable Batteries

The electrochemical parameters of a novel binder-free self-standing biomimetic cathode based on lithium manganese oxide (LMO) and carbon nanotubes (CNT) for rechargeable Lithium-ion aqueous batteries (ReLIAB) are improved using polyaniline (PANI) core-shell in situ polymerization and graphene (Gr). The fabricated cathode material exhibits the so-called “tectonic plate island bridge” biomimetic structure. This constitution is created by combining three components as shown by a SEM and a TEM analysis: the Gr substrates support an entangled matrix of conductive CNT which connect island of non-conductive inorganic material composed of LMO. The typical spinel structure of the LMO remains unchanged after modifying the basic structure with Gr and PANI due to a simplified hydrothermal method used for synthesis. The Gr and PANI core-shell coating improves the electric conductivity from 0.0025 S/cm up to 1 S/cm. The electrochemical performances of the LMO/CNT-Gr/PANI composite electrode are optimized up to 136 mA h g⁻¹ compared to 111 mA h g⁻¹ of the LMO/CNT. Besides that, the new electrode shows good cycling stability after 200 galvanostatic charging/discharging cycles, making this structure a future candidate for cathode materials for ReLIAB.

Electrochemical performance of composite electrodes based on rGO, Mn/Cu metal-organic frameworks, and PANI

Benzendicarboxylic acid (BDC)-based metal–organic frameworks (MOFs) have been widely utilized in various applications, including supercapacitor electrode materials. Manganese and copper have solid diamond frames formed with BDC linkers among transition metals chosen for MOF formation. They have shown the possibility to enlarge capacitance at different combinations of MOFs and polyaniline (PANI). Herein, reduced graphene oxide (rGO) was used as the matrix to fabricate electrochemical double-layer SCs. PANI and Mn/Cu-MOF's effect on the properties of electrode materials was investigated through electrochemical analysis. As a result, the highest specific capacitance of about 276 F/g at a current density of 0.5 A/g was obtained for rGO/Cu-MOF@PANI composite.