The NiFe2O4/NiCo2O4/GO composites electrode material derived from dual-MOF for high performance solid-state hybrid supercapacitors

PVP-assisted MOF-derived Fe3O4/C powders for microwave absorption applications

Metal-organic framework (MOF) derived porous Fe3O4/C powders were applied for absorption of microwaves in the frequency range of 1-18 GHz. The effects of the polyvinylpyrrolidone (PVP) additive on the synthesis of MIL101-(Fe) precursor were studied by various characterization methods. By adding PVP, the impure hematite phase (α-Fe2O3) with magnetite phase (Fe3O4) was disappeared and the particular morphology was transformed to the porous rod-like, leading to the increase of specific surface area from 150 to 282 m2/g. Furthermore, the saturation magnetization (Ms) of Fe3O4/C powders reached a maximum value of 47 emu/g at a proper amount of PVP. A thin absorber (2.6 mm) made of 50 wt% Fe3O4/C powders and 50 wt % paraffine absorbed the whole of X frequency band (8-12 GHz) with a minimum reflection loss of -20 dB at a matching frequency of 10 GHz. Adjusting the permittivity and permeability parameters of the Fe3O4/C powders via adding PVP was responsible for their better microwave absorption performance.

Facile preparation of NiFe2O4 decorated chitosan-graphene oxide for efficient remediation of Co(II) and adsorption mechanism

In the background of severe water pollution, adsorption is a charming technique for heavy metal remediation. In this work, NiFe2O4 decorated chitosan-graphene oxide (NFCG) was prepared by simple hydrothermal method for Co(II) remediation application. Adsorption mechanism was elaborately elucidated based on multiple evidences extracted from adsorption fitting (isotherms, thermodynamics and kinetics), spectroscopic test (XPS, UV-Vis absorption, fluorescent emission and Raman spectra) and the hard-soft acid-base (HSAB) theory inspection. Result shows, for Co(II) with initial concentration 200 mg·L-1, NFCG with dosage 500 mg·L-1 reaches adsorption equilibrium in 24 min, rendering removal percentage and adsorption amount 96.87 % and 387.48 mg·g-1, respectively. Owing to the efficient recovery enabled by paramagnetism, NFCG keeps adsorption amount 311.01 mg·g-1 for Co(II) after six consecutive cycles. Moreover, NFCG exhibits selectivity towards Co(II) under the coexistence of common interfering substances. Adsorption fitting suggests chemical adsorption based on heterogeneous affinity. Spectroscopic analysis discloses, CO, CO, -C(=O)NH-, OH and aromatic part contribute to Co(II) adsorption via electron donation, forming CoO bond. This atomic scale adsorption mechanism was substantiated by HSAB theory calculation. In brief, this work provides basic knowledge and technical support for fabricating high efficiency magnetic bio adsorbent.

Preparation of Zirconium-Based MOF-Derived Phosphide on GO/MXene Double Substrates for High-Performance Asymmetric Supercapacitors

At present, it is very necessary to select and prepare suitable positive and negative electrode materials to fabricate high-performance asymmetric supercapacitors. Metal-organic frameworks (MOFs) have garnered significant attention in the energy storage field due to their high conductivity. As a branch, the zirconium organic framework (UIO-66) is a promising porous material due to its large specific surface area and abundant Zr centers. Graphene oxide (GO) and MXene are very suitable as substrate materials for conducting an MOF due to their abundant active sites and adjustable interlayer distance. The GO/MXene@NiZrP prepared through an in situ composite of GO and Mxene with the hydrothermal method and calcining method showed excellent electrochemical performance. Compared with the precursor UIO-66, the specific capacitance of the final product GO/MXene@NiZrP increases more than ten times, mainly because of its special layered porous structure, and GO/MXene@NiZrP has a larger specific surface area, pore volume, and surface defects caused by unstable Zr4+ than those of UIO-66. Using GO/MXene@NiZrP as the positive electrode and biochar (BC) as the negative electrode, an asymmetric supercapacitor, BC//GO/MXene@NiZrP, is assembled. After 10,000 cycles at a current density of 10 A g-1, the capacitance retention remains at 83.3%, showing excellent cycle stability.

Recent Trends in Supercapacitor Research: Sustainability in Energy and Materials

Supercapacitors (SCs) have emerged as critical components in applications ranging from transport to wearable electronics due to their rapid charge-discharge cycles, high power density, and reliability. This review offers an analysis of recent strides in supercapacitor research, emphasizing pivotal developments in sustainability, electrode materials, electrolytes, and 'smart SCs' designed for modern microelectronics with attributes such as flexibility, stretchability, and biocompatibility. Central to this discourse are two dominant electrode materials: carbon materials (CMs), primarily in electric double layer capacitors (EDLCs), and pseudocapacitive materials, involving oxides/hydroxides, chalcogenides, metal-organic frameworks, conductive polymers and metal nitrides such as MXene. Despite EDLCs' historical use, challenges such as low energy density persist, with heteroatom introduction into the carbon lattice seen as a solution. Concurrently, pseudocapacitive materials dominate recent studies, with efficiency enhancement strategies, such as the creation of hybrids based on different types of materials, surface structural engineering and doping, under exploration. Electrolyte innovation, especially the shift towards gel polymer electrolytes for flexible SCs, and the harmonization of electrode materials with SC designs are highlighted. Emphasis is given to smart SCs with novel attributes such as self-charging, self-healing, biocompatibility, and environmentally conscious designs. In summary, the article underscores the drive in sustainable supercapacitor research to achieve high energy and power density, steering towards SCs that are efficient and versatile and involving bioderived/biocompatible SC materials. This brief review is based on selected recent references, offering depth combined with an accessible overview of the SC landscape.

Manganese-cobalt hydroxide nanosheets anchored on a hollow sulfur-doped bimetallic MOF for high-performance supercapacitors and the hydrogen evolution reaction in alkaline media

Nonmetallic doping and in situ growth techniques for designing electrode materials with excellent electrocatalytic activity are effective strategies to enhance the electrochemical performance. Bifunctional electrode materials for supercapacitors (SCs) and the hydrogen evolution reaction (HER) have attracted great interest due to their potential applications in green energy storage and conversion. Herein, the bimetallic MnCo LDH is anchored on a hollow sulfur (S)-doped MnCo-MOF-74 surface, forming a poplar flower-like 3D composite which is used for SCs and the HER in alkaline media. The fabricated S-MnCo-MOF-74@MnCo LDH/NF electrode exhibits a favorable specific capacitance of 1875.4 F g-1 at 1 A g-1 and steady long-term cycling performance. Moreover, the assembled HSC using S-MnCo-MOF-7@MnCo LDH/NF as the cathode material and active carbon (AC) as the anode material shows 546.4 F g-1 capacitance (1 A g-1) with a maximum energy density of 58 W h kg-1 at 14 000 W kg-1 power density. As an electrocatalyst, S-MnCo-MOF-7@MnCo LDH/NF exhibits excellent HER properties with a small Tafel slope of 128.9 mV dec-1 a low overpotential of 197 mV at 10 mA cm-2 and durable performance for 10 hours in alkaline media. The present work provides insights into understanding and designing active electrode materials for stable hydrogen evolution and high-performing supercapacitors in an alkaline environment.

Current Trends and Promising Electrode Materials in Micro-Supercapacitor Printing

The development of scientific and technological foundations for the creation of high-performance energy storage devices is becoming increasingly important due to the rapid development of microelectronics, including flexible and wearable microelectronics. Supercapacitors are indispensable devices for the power supply of systems requiring high power, high charging-discharging rates, cyclic stability, and long service life and a wide range of operating temperatures (from -40 to 70 °C). The use of printing technologies gives an opportunity to move the production of such devices to a new level due to the possibility of the automated formation of micro-supercapacitors (including flexible, stretchable, wearable) with the required type of geometric implementation, to reduce time and labour costs for their creation, and to expand the prospects of their commercialization and widespread use. Within the framework of this review, we have focused on the consideration of the key commonly used supercapacitor electrode materials and highlighted examples of their successful printing in the process of assembling miniature energy storage devices.

A sensing platform based on Cu-MOF encapsulated Dawson-type polyoxometalate crystal material for electrochemical detection of xanthine

A promising sensing platform based on polyoxometalate-based metal-organic framework (POMOF) was established for sensitive electrochemical detection of xanthine (XA). In the unique structure of POMOF, the Dawson polyoxoanions P₂W₁₈ were encapsulated into 3D open copper-mixed ligand nanotube framework Cu-MOF, in which the cavity of the metal-organic framework provides a specific shelter to prevent the aggregation and loss of polyoxometalate in electrocatalytic reactions; meanwhile, unsaturated Cu(II) active sites of Cu-MOF can also serve as electrocatalytic active center. The POMOF-based sensor (CuMOFP₂W₁₈/XC-72R) was fabricated by using acetylene black (XC-72R) as a support material to enhance the conductivity of POMOF. The performances of the POMOF-based sensor were studied by using different electrochemical testing methods. The composite displayed remarkable electrocatalytic activity for the oxidation of XA due to the synergistic effect of polyoxometalate (POM) and metal-organic framework (MOF). The electrochemical sensor demonstrated a wide linear range (0.5 μM-240 μM), low detection limit (0.26 μM), and excellent selectivity for detecting XA. Furthermore, the composite further demonstrated excellent reproducibility and great stability. More importantly, the proposed sensor was utilized to detect XA in real samples, which may provide a new way for early disease diagnosis.

One-Step Solvothermal Synthesis of Raspberry-like NiCo-MOF for High-Performance Flexible Supercapacitors for a Wide Operation Temperature Range

As a novel electrode material for energy storage, metal-organic frameworks (MOFs) emerge with plenty of merits and certain drawbacks in the field of supercapacitors. Nevertheless, most MOFs synthesized for the moment are faced with dimension/distribution issues and dissatisfactory electrical conductivity. Hence, in this paper, NiCo-MOF was successfully fabricated by applying a one-step solvothermal method, from which NiCo-MOF-3 presents an optimal electrochemical performance compared to other NiCo-MOFs and Ni/Co-MOF. Owing to its unique three-dimensional spherical raspberry structure, NiCo-MOF-3 demonstrates an available internal resistance and electron transfer resistance to ameliorate electrical energy storage, exhibiting an excellent mass specific capacitance of 639.8 F/g at 1 A/g. Then, a flexible quasi-solid-state asymmetric supercapacitor was assembled with NiCo-MOF-3 as the positive electrode. The introduction of K₃[Fe(CN)₆] and glycerin in the gel electrolyte facilitates the maximum energy density of 66.3 Wh/kg of the device, with a corresponding power density reaching its maximum of 12,047 W/kg. The device's apparent energy density, excellent flexibility, and temperature resistance reveal that our method to prepare supercapacitor electrode material possesses more advantages than those in the former literature.

Dual-ZIF-derived "reassembling strategy" to hollow MnCoS nanospheres for aqueous asymmetric supercapacitors

Construction of delicate nanostructures with a facile, mild-condition and economical method is a key issue for building high-performance electrode materials. We demonstrate a facile and novel "reassembling strategy" to hollow MnCoS nanospheres derived from dual-ZIF for supercapacitors. The spherical shell's surface structure, thickness and Mn distribution were controlled by regulating the solvothermal reaction time. The chemical composition, phases, specific surface areas and microstructure were studied and the electrochemical performances were systematically estimated. As the unique low-crystalline and optimized hollow nanosphere structure contributes to increasing active sites, MnCoS nanospheres exhibit excellent electrochemical performance. The test results show that the specific capacitance increases with increasing solvothermal time, and the MCS with a 5 h reaction time exhibits optimal electrochemical properties with a high specific capacity of 957 C g-1 (1 A g-1). Furthermore, an MCS-5//AC asymmetric supercapacitor device delivers a specific energy as high as 36.9 W h kg-1 at a specific power of 750 W kg-1.

Metal-organic framework functionalized poly-cyclodextrin membranes confining polyaniline for charge storage

Crystals of a metal-organic framework, UiO-66, are grown on electrospun crosslinked poly-cyclodextrin (poly-CD) fibrous membranes with an ultrahigh coverage, and polyaniline (PANI) is further confined within the MOF pores. The obtained PANI@UiO-66/poly-CD membranes are used as free-standing electrodes towards use in wearable energy-storage devices.

Block copolymer-assisted synthesis of VO2 (B) microflowers for supercapacitor applications

Nanoporous metal oxides are appealing candidates for energy storage applications as they can interact with guest species from inner and outer surfaces, leading to improved energy and power density performance. We have synthesized VO₂ (B) microflowers with a stable phase and tailored porous structures utilizing block copolymers to achieve excellent supercapacitor performance.

Design of ZIF-67 MOF-derived Co3O4/NiCo2O4 nanosheets for supercapacitor electrode materials

Binary transition metal oxides exhibit improved properties including good redox potentials and electrical conductivities compared with single metal oxides as electrode materials in energy storage. Herein, ZIF-67 is prepared by a one-step method using Co2+ as the central metal ion, 2-methylimidazole as the organic ligand, and methanol as an organic solvent at room temperature. Hollow NiCo2O4 and sheet-like Co3O4/NiCo2O4 derived from bimetallic imidazolate framework precursors were synthesized by adding cobalt and nickel ions in appropriate proportions. A hollow and porous structure is achieved for the reaction between a nickel salt and ZIF-67, and this unique nanostructure provides a high active surface area, which is beneficial to the electrochemical properties. Several samples are prepared and used as electrode materials for electrochemical tests in 6 M KOH. As a result, the Co3O4/NiCo2O4 electrode with a sheet nanostructure showed a high specific capacitance of 846 F g−1 at a current density of 0.5 A g−1. This Co3O4/NiCo2O4 electrode material is promising for future studies on high-performance supercapacitors to solve emerging energy-related problems.

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Highly improved supercapacitance properties of MnFe2O4 nanoparticles by MoS2 nanosheets

Manganese ferrite (MnFe₂O₄) nanoparticles were synthesized via a hydrothermal method and combined with exfoliated MoS₂ nanosheets, and the nanocomposite was studied as a supercapacitor. X-ray diffractometry and Raman spectroscopy confirmed the crystalline structures and structural characteristics of the nanocomposite. Transmission electron microscopy images showed the uniform size distribution of MnFe₂O₄ nanoparticles (~ 13 nm) on few-layer MoS₂ nanosheets. UV-visible absorption photospectrometry indicated a decrease in the bandgap of MnFe₂O₄ by MoS₂, resulting in a higher conductivity that is suitable for capacitance. Electrochemical tests showed that the incorporation of MoS₂ nanosheets largely increased the specific capacitance of MnFe₂O₄ from 600 to 2093 F/g (with the corresponding energy density and power density of 46.51 Wh/kg and 213.64 W/kg, respectively) at 1 A/g, and led to better charge-discharge cycling stability. We also demonstrated a real-world application of the MnFe₂O₄/MoS₂ nanocomposite in a two-cell asymmetric supercapacitor setup. A density functional theory study was also performed on the MnFe₂O₄/MoS₂ interface to analyze how a MoS₂ monolayer can enhance the electronic properties of MnFe₂O₄ towards a higher specific capacitance.