A high-performance hybrid supercapacitor with NiO derived NiO@Ni-MOF composite electrodes

A comparative study on the synthesis strategies and electrochemical features of bimetallic Cu/Co-MOFs

In this work, three distinct synthetic procedures-step-by-step (CC-1), single-step (CC-2), and simple mixing (CC-3)-were utilized to investigate their effects on the formation of heterostructures in bimetallic Cu/Co-MOFs. The resulting MOF crystal structures revealed a 1 : 1 ratio of Co to Cu metal ions, and compared their electrochemical activities with a simple mixture of individual MOFs. To maximize the benefits of these synthesis approaches for supercapacitor uses, electrochemical analyses were conducted. Results revealed that the capacitance of CC-1 was 438 F g-1 at 1 A g-1, which was 1.14 times and 2.76 times higher than those of the CC-2 and CC-3 samples, respectively. This notable performance was attributed to the synergistic contributions from each 2D material component and the formation of a stable heterostructure that resulted from an optimal metal-ion loading. The best-performing CC-1 electrode was further tested in both asymmetric (AD) and symmetric (SD) coin cell devices. AD demonstrated an energy density (ED) of 40.4 W h kg-1 through a power density (PD) of 302.3 W kg-1 with 75% stability, while the SD device displayed an ED of 15.7 W h kg-1 and a PD of 346.7 W kg-1 with 88% stability.

Facile and cost-effective NiO/MgO-SiO2 composites for efficient oxygen evolution reaction and asymmetric supercapacitor systems

Biomass waste from grapefruit peel extract was used for the preparation of MgO-SiO2 composites in situ in order to develop effective electrocatalytic composites based on NiO/MgO-SiO2. The MgO-SiO2 composites were subsequently deposited with NiO using a modified hydrothermal method. The synthesized materials were analyzed to investigate their morphology, crystal structure, chemical composition, functional group, and optical band gap. The structural analysis allowed us to determine the orientation of the nanoparticles, the cubic phase of NiO and MgO, the significant loss of optical band gap, and the enriched functional groups on the surface of NiO/MgO-SiO2 composites. The electrochemical properties were investigated in the presence of an alkaline solution of KOH. To study the oxygen evolution reaction (OER) in 1 M KOH aqueous solution, different NiO/MgO-SiO2 composites were investigated. It was found that the NiO/MgO-SiO2 composite that contained the highest amount of MgO-SiO2 (sample 3) had a lower overpotential than the NiO/MgO-SiO2 composite with the lowest amount of MgO-SiO2. Sample 3 exhibited an overpotential of 230 mV at 10 mA cm-2 over a period of 40 hours with excellent stability. The superior electrochemical activity of the NiO/MgO-SiO2 composite (sample 3) was demonstrated in an energy storage device using 3 M KOH aqueous solution, and asymmetric supercapacitor devices were fabricated in 3 M KOH solution. According to the ASC's specifications, a specific capacitance of 344.12 F g-1 and an energy density of 7.31 W h kg-1 were found for the device at a fixed current density of 1.5 A g-1. After over 40 000 galvanic charge-discharge repeatable cycles at 1.5 A g-1, sample 3 of the NiO/MgO-SiO2 composite exhibited excellent cycling stability with 88.9% percent capacitance retention. During the performance evaluation of the NiO/MgO-SiO2 composites, grapefruit peel extract was confirmed as a potential biomass waste for the fabrication of high-performance energy conversion and storage devices.

Oxalate-derived porous C-doped NiO with amorphous-crystalline heterophase for supercapacitors

Constructing amorphous/crystalline heterophase structure with high porosity is a promising strategy to effectively tailor the physicochemical properties of electrode materials and further improve the electrochemical performance of supercapacitors. Here, the porous C-doped NiO (C-NiO) with amorphous/crystalline heterophase grown on NF was prepared using NF as Ni source via a self-sacrificial template method. Calcining the self-sacrificial NiC2O4 template at a suitable temperature (400 °C) was beneficial to the formation of porous heterophase structure with abundant cavities and cracks, resulting in high electrical conductivity and rich ion/electron-transport channels. The density functional theory (DFT) calculations further verified that in-situ C-doping could modulate the electronic structure and enhance the OH- adsorption capability. The unique porous amorphous/crystalline heterophase structure greatly accelerated electrons/ions transfer and Faradaic reaction kinetic, which effectively improved the charge storage. The C-NiO calcined at 400 °C (C-NiO(400)) displayed a markedly enhanced specific charge, outstanding rate property and excellent cycling stability. Furthermore, the hybrid supercapacitor assembled by C-NiO(400) and active carbon achieved a high energy density of 49.0 Wh kg-1 at 800 W kg-1 and excellent cycle stability (90.9 % retention at 5 A/g after 10 000 cycles). This work provided a new strategy for designing amorphous/crystalline heterophase electrode materials in high-performance energy storage.

The response to shock loads of Ni-MOF and NiO NPs on aerobic granular sludge and algal-bacterial aerobic granular sludge

Currently, the increasing use of nickel metal-organic frameworks (Ni-MOF) and nickel oxide nanoparticles (NiO NPs) has raised concerns regarding their potential environmental impact on wastewater treatment systems. Herein, the responses of aerobic granular sludge (AGS) and algal-bacterial aerobic granular sludge (AB-AGS) to Ni-MOF and NiO NPs were investigated. The results showed that Ni-MOF concentrations of 50, 100, and 200 mg/L significantly reduced nutrient removal in both systems, particularly affecting ammonia, nitrite, and phosphorus removal, while denitrification processes remained stable. AB-AGS exhibited greater tolerance to nickel than AGS, likely due to its higher content of extracellular polymeric substances (EPSs), in which the algae were embedded, indicating a robust bacterial-algal symbiotic system. Conversely, NiO NPs had no adverse effects on bioreactor performance, likely due to their insolubility and integration into the sludge matrix. This research provides valuable insights into the potential future applications of AGS and AB-AGS technologies for treating wastewater contaminated with nickel and other heavy metals, highlighting the superior resilience of AB-AGS to nickel exposure.

First investigation of high-performance FeS-based W18O49 asymmetric supercapacitors operating at 1.6 V

This study presents a comprehensive evaluation of FeS-W18O49 composite electrodes, revealing their exceptional performance for supercapacitor applications. Fabricated via a wet-chemical method, the FeS-W18O49 composites demonstrated a high specific capacitance of 558 F g-1 at a current density of 1 A g-1, showcasing their outstanding charge storage capabilities. The composites achieved an energy density of 89.77 W h kg-1 and a power density of 4950 W kg-1, attributed to the synergistic effect between the excellent electrical conductivity of FeS and the redox activity of W18O49, which collectively enhance the electrode's electrochemical performance. Moreover, the FeS-W18O49 electrodes exhibited remarkable cycling stability, retaining 87.6% of their capacitance after 10 000 charge-discharge cycles. These findings underscore the potential of FeS-W18O49 composites to advance supercapacitor technology by improving energy storage capacity and extending cycle life.

Phytochemical-enhanced NiO nanostructures for superior oxygen evolution and asymmetric supercapacitor applications

The development of new energy conversion and storage technologies has contributed to the widespread use of renewable energy. However, new methodologies for electrochemical energy storage systems remain to be developed. This study presents a facile, low-cost, scalable, and environmentally friendly method for the synthesis of nickel oxide (NiO) nanostructures by hydrothermal methods using lotus root extract. The different volumes of lotus root extract were tested on NiO nanostructures (sample 1, sample 2) using 1 ml and 2 ml amounts of the extract, respectively. Therefore, phytochemicals from lotus extract have influenced the surface morphology, crystal quality, optical band gap, electrical conductivity, and surface active sites of NiO nanostructures. Sample 2 of the NiO nanostructures was found to be highly active for oxygen evolution reaction (OER) and showed an overpotential of 380 mV at 10 mA cm−2 and a durability of 30 h at 10 mA cm−2. Furthermore, sample 2 of NiO has shown specific capacitance of 1503.84 F g−1 at 2 A g−1 as well as cycling stability over a period of forty thousand GCD cycles. The percentage specific capacitance retention were highly improved up to 100.6%. An asymmetric energy storage device has been constructed using NiO sample 2 as the anode electrode material, demonstrating excellent specific capacity of about 1113 C g−1 at 5 A g−1. For the asymmetric supercapacitor device, a power density of 20000 W kg−1 and an energy density of 245 Wh kg−1 were obtained. In a study of cycling stability for 40000 GCD cycles, it was observed that the asymmetric device retained 96.86% of its specific capacitance. A significant contribution was made to the electrochemical performance of sample 2 of NiO by phytochemicals derived from lotus extract.

Fabrication of composite GO/NiFe2O4-MnFe2O4-CoFe2O4 anode material: Toward high performance hybrid supercapacitors

Here, NiFe2O4, MnFe2O4, and CoFe2O4 nanoferrites are prepared by coprecipitation synthesis technique from nickel, manganese, and cobalt chloride precursors. Synthesized nanoferrites are annealed by calcination process at 800°C for 2 h. To produce a novel anode electrode material for asymmetric supercapacitors (ASCs), the composite material of GO/NiFe2O4-MnFe2O4-CoFe2O4 is fabricated. Physicochemical aspects of the synthesized nanoferrites are evaluated. X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and x-ray photoelectron spectroscopy tests are conducted, respectively. The electrochemical activities are studied by cyclic voltammetry, glavanostatic charge-discharge, and electrochemical impedance spectroscopy (EIS) in 2 M KOH as the electrolyte. In three electrode system, the novel GO/NiFe2O4-MnFe2O4-CoFe2O4 electrode displays a high specific capacity of 325 C g-1 and preserves about 99.9% of its initial specific capacity. The GO/NiFe2O4-MnFe2O4-CoFe2O4//GO ASCs device is assembled using GO/NiFe2O4-MnFe2O4-CoFe2O4, GO, and 2 M KOH solution as the positive electrode, negative electrode, and electrolyte, respectively. Significantly, the GO/NiFe2O4-MnFe2O4-CoFe2O4//GO ASCs represent an outstanding energy density of 50.5 W h kg-1 at power density of 2560 W kg-1. Through the long-term charge discharge cycling tests, this ASC device illustrates about 93.7% capacity retention after 3000 cycles. Then, the present study provides the NiFe2O4-MnFe2O4-CoFe2O4 composite nanoferrites as a novel favorable candidate for anode material. RESEARCH HIGHLIGHTS: Simple and green synthesis of magnetic NiCo2O4/NiO/rGO composite nanostructure using natural precursor. Fabricating and designing an efficient semiconductor for degradation ability. NiCo2O4/NiO/rGO nanocomposite with advanced photo elimination catalytic routine. The photocatalytic performance of NiCo2O4/NiO/rGO was surveyed for the degradation of various antibiotics below visible radiation. Efficiency was 92.9% to eliminate tetracycline. We developed a synergetic approach to prepare a novel active material composed of GO/ NiFe2O4-MnFe2O4-CoFe2O4 by a hybrid electrode material. Green synthesis method was accomplished to attain NiCo2O4/NiO/rGO nanocomposite with advanced photo elimination catalytic routine. The oxide nanobundles were prepared with a rapid and eco-friendly method. In order to investigation of the effect of natural precursor, morphology and shape of nanoproducts was compared. NiCo2O4/NiO/rGO nanobundles possess a suitable bandgap in the visible area.

Fabrication and assembly of supercapacitors based on Ni-based MOFs and their derivative materials for enhancing their electrochemical performances

Metal-organic frameworks (MOFs) are a class of porous materials that have been gradually applied in the field of supercapacitors, but they still present major challenges due to their inherent instability and poor conductivity. Herein, in order to solve these problems, Ni-based MOFs and their derivative materials with a particular spherical structure were prepared using a special calcination method. This unique structure not only improves the conductivity of the electrode, but also promotes the transport of electrons and ions during the electrochemical energy storage process. The as-prepared Ni-MOF@M-a4 has an amazing specific capacitance (637.78 F g-1) and a relatively low impedance. The fabricated asymmetric supercapacitor (ASC) consisted of Ni-MOF@M-a4 and activated carbon (AC) as positive and negative electrodes, respectively. The specific capacitance of this ASC was 18.14 F g-1. The maximum energy and power densities of the device reached 1.23 W h kg-1 and 175.00 W kg-1, showing good electrochemical performance. In this work, both an innovative strategy for the rational preparation of MOF arrays with good orientation and a special material preparation method are proposed, which have promising application potential in the field of asymmetric supercapacitors.

MOFs-Based Materials with Confined Space: Opportunities and Challenges for Energy and Catalytic Conversion

Metal-Organic Frameworks (MOFs) are a very promising material in the fields of energy and catalysis due to their rich active sites, tunable pore size, structural adaptability, and high specific surface area. The concepts of "carbon peak" and "carbon neutrality" have opened up huge development opportunities in the fields of energy storage, energy conversion, and catalysis, and have made significant progress and breakthroughs. In recent years, people have shown great interest in the development of MOFs materials and their applications in the above research fields. This review introduces the design strategies and latest progress of MOFs are included based on their structures such as core-shell, yolk-shell, multi-shelled, sandwich structures, unique crystal surface exposures, and MOF-derived nanomaterials in detail. This work comprehensively and systematically reviews the applications of MOF-based materials in energy and catalysis and reviews the research progress of MOF materials for atmospheric water harvesting, seawater uranium extraction, and triboelectric nanogenerators. Finally, this review looks forward to the challenges and opportunities of controlling the synthesis of MOFs through low-cost, improved conductivity, high-temperature heat resistance, and integration with machine learning. This review provides useful references for promoting the application of MOFs-based materials in the aforementioned fields.

Biogenic synthesis of nickel cobaltite nanoparticles via a green route for enhancing the photocatalytic and electrochemical performances

Green synthesis aligns with the global demand for eco-friendly and sustainable technologies, reducing the dependency on harmful chemicals and high-energy processes typically used in conventional synthesis techniques. This study highlights a novel green synthesis route for nickel cobaltite nanoparticles (NiCO2O4 NPs) utilizing Hyphaene thebaica extract as a natural reducing and stabilizing agent. The synthesized NiCO2O4 NPs, with sizes ranging from 20 to 30 nm, exhibited uniform diamond-like structures as confirmed by SEM and TEM imaging. XRD analysis verified the polycrystalline nature of these nanoparticles, while EDS measurements confirmed the elemental composition of Ni and Co. The presence of functional groups was subsequently verified through FT-IR analysis, and Raman spectroscopy further confirmed phase formation. Electrochemical evaluations revealed significant pseudocapacitive behavior, showing a specific capacitance of 519 F/g, demonstrating their potential for high-performance supercapacitors. To further assess the applicability of the synthesized NiCO2O4 NPs, their photocatalytic activity against methylene blue (MB) dye was investigated, resulting in a 99% degradation rate. This impressive photocatalytic efficiency highlights their potential application in environmental remediation. Overall, this work underscores the significant potential of green synthesis methods in producing high-performance nanomaterials while simultaneously reducing environmental impact and promoting sustainable development.

A MOF-derived flower-shaped CeCo-oxide as a multifunctional material for high-performance lithium-ion batteries and supercapacitors

Precursor method is a well-known technology for preparing certain functional materials. In this work, a novel 3d-4f bimetallic organic framework, denoted as 45MCeCo (45 M representing 4,5-imidazole dicarboxylic acid), was successfully synthesized via a hydrothermal technique. The compound thus obtained has the molecular formula of C10H11CeCoN4O12. By meticulously controlling the amounts of the experimental materials, it was feasible to prepare flower-like crystals possessing identical single crystal structures and significantly larger specific surface areas. As a precursor for electrode materials, this structure underwent calcination at different temperatures to prepare Co3O4/CeO2 composites with in situ composite heterostructures. Post-electrochemical tests revealed that CeO2 remains unreactive across all potentials, thereby contributing to the stabilization of the electrode material structure. In contrast, Co3O4 participated in redox reactions to provide a specific capacity to the sample. In addition, when comparing the performance of the electrode material under different calcination conditions, it became evident that the material exhibited optimal electrochemical performance when subjected to a temperature of 700 °C for 2 h.

Facile synthesis of a three-dimensional Ln-MOF@FCNT composite for the fabrication of a symmetric supercapacitor device with ultra-high energy density: overcoming the energy storage barrier

In order to quench the thirst for efficient energy storage devices, a novel praseodymium-based state-of-the-art three-dimensional metal-organic framework (MOF), {[Pr(pdc)2]Me2NH2}n (YK-1), has been synthesized by using a simple solvothermal method employing a readily available ligand. YK-1 was characterised by single-crystal XRD and crystallographic analysis. The electrochemical measurements of YK-1 show that it exhibits a specific capacitance of 363.5 F g-1 at a current density of 1.5 A g-1 with 83.8% retention after 5000 cycles. In order to enhance its electrochemical performance for practical application, two composites of YK-1 with graphene oxide (GO) and functionalised multi-walled carbon nanotubes (FCNTs), namely YK-1@GO and YK-1@FCNT, were fabricated by employing a facile ultrasonication technique. The as-synthesized MOF and the composites were characterized by PXRD, FTIR, SEM, and TEM techniques. YK-1@GO and YK-1@FCNT offer enhanced specific capacitances of 488.2 F g-1 and 730.2 F g-1 at the same current density with 93.8% and 97.7% capacity retention after 5000 cycles, respectively (at 16 A g-1). Fascinated by the outstanding results shown by YK-1@FCNT, a symmetric supercapacitor device (SSC) based on it was fabricated. The assembled SSC achieved a remarkable energy density (87.6 W h kg-1) and power density (750.2 W kg-1) at a current density of 1 A g-1, along with very good cycling stability of 91.4% even after 5000 GCD cycles. The SSC device was able to power up several LED lights and even operated a DC brushless fan for a significant amount of time. To the best of our knowledge, the assembled SSC device exhibits the highest energy density among the MOF composite-based SSCs reported so far.

Morphology regulation of conductive metal-organic frameworks in situ grown on graphene oxide for high-performance supercapacitors

In this work, nickel-catecholate (Ni-CAT) nanorods were in situ compounded on graphene oxide (GO) to form a composite Ni-CAT@GO (NCG) with a special "blanket-shape" structure, which was used as an electrode material for supercapacitors. The morphology of Ni-CATs in situ grown on GO was modulated by introducing various contents of GO. With increasing GO, the length of nanorods of Ni-CATs is obviously shortened, and the charge transfer resistance of NCG is significantly reduced as the GO content is relatively low while it increases with further addition of GO, because excessive GO in NCG results in smaller crystal sizes accompanied by smaller stacking pores. Both the over-long Ni-CAT nanorods and the smaller stacking pores can restrict the accessible surface areas for the electrolyte. Optimal nanorod sizes are crucial to achieve good electrochemical performance for electrode materials. Galvanostatic charge-discharge analysis of NCG electrodes shows that their capacity initially increases and then decreases with the addition of more and more GO, and Ni-CAT@GO-0.5 (NCG0.5) with minimal charge transfer resistance exhibits the best electrochemical performance. The results demonstrate that the NCG0.5 electrode with optimal morphology possesses an excellent capacitance of 563.8 F g-1 at 0.5 A g-1 and a good rate performance of 61.9% at 10 A g-1, indicating that Ni-CAT@GO is a new type of promising electrode material for supercapacitors based on conductive metal-organic frameworks.

Improved Electrochemical Performance of Aqueous Hybrid Supercapacitors Using CrCo2O4 Mesoporous Nanowires: An Innovative Strategy toward Sustainable Energy Devices

High-rate aqueous hybrid supercapacitors (AHSCs) have attracted relevant scientific significance owing to their expected energy density, supercapacitor-level power density, and battery-level energy density. In this work, a bimetallic nanostructured material with chromium-incorporated cobalt oxide (CCO, i.e., CoCr2O4) was prepared via a hydrothermal method to form a stable cubic obelisk structure. Compared with CCO materials prepared using traditional methods, CCO displayed a nanowire structure (50 nm diameter), suggesting an enhanced specific surface area and a large number of active sites for chemical reactions. The electrode possessed a high specific capacitance (2951 F g-1) at a current density of 1 A g-1, minimum Rct (0.135 Ω), and the highest capacitance retention (98.7%), making it an ideal electrode material for AHSCs. Ex situ analysis based on X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) showed a favorable stability of CCO after 10,000 cycles without any phase changes being detected. GGA and GGA + U methods employed in density functional theory (DFT) also highlighted the enhanced metallic properties of CCO originating from the synergistic effect of semiconducting Cr2O3 and Co3O4 materials.

Unleashing Enhanced Energy Density with PANI/NiO/Graphene Nanocomposite in a Symmetric Supercapacitor Device, Powered by the Hybrid PVA/Na2SO4 Electrolyte

In this study, a PANI/NiO/Graphene (PNG) nanocomposite was synthesized using a cost-effective wet chemical polymerization method. This nanocomposite was used to fabricate supercapacitor electrodes in a nontoxic, noncorrosive, and neutral hybrid gel polymer (PVA/Na2SO4) electrolyte. The electrodes made from the PNG material underwent analysis using electrochemical techniques, including cyclic voltammetry (CV) and electrochemical impedance spectroscopy in a three-electrode system. For a deeper exploration of the supercapacitive properties of the PNG material, galvanostatic charge-discharge was employed. A practical two-electrode symmetric device powered by the hybrid PVA/Na2SO4 electrolyte was fabricated to calculate specific capacitance, energy density, and power density. The designed PNG material demonstrates excellent electrochemical behavior, exhibiting an improved energy density of 59.41 W h/kg at 850 W/kg. Furthermore, the PNG electrode shows excellent reversibility along with enhanced energy density and retains 89% of its capacitance after 2000 cycles. These outstanding properties of the PNG material can be attributed to the synergistic effect of PANI nanofibrous, NiO, and graphene two-dimensional structures.

4-Methyl-5-vinyl thiazole modified Ni-MOF/g-C3N4/CdS composites for efficient photocatalytic hydrogen evolution without precious metal cocatalysts

The construction of heterojunction systems is an effective way to efficiently generate hydrogen by water photolysis. In this work, Ni-MOF (trimesic acid, (BTC)) and g-C3N4 (denoted as CN) were combined, and then Ni-MOF/CN was modified by 4-Methyl-5-vinyl thiazole (denoted as MVTh). Finally, CdS was loaded on the surface of Ni-MOF/CN/MVTh to prepare the photocatalyst Ni-MOF/g-C3N4/MVTh/CdS (denoted as Ni/CN/M/Cd) with a triangular closed-loop path heterojunction for the first time. As a photocatalyst without precious metal cocatalysts, Ni/CN/M/Cd displayed high H2 evolution (17.844 mmol·g-1·h-1) under an optimum CdS loading of 40 wt%. The H2 evolution rate was approximately 79 times that of Ni-MOF/CN and exceeded those of almost all catalysts based on MOF/CN in the literature. The triangular closed-loop heterojunction formed between Ni-MOF, g-C3N4, and CdS could realize the directional migration of photocarriers and significantly diminished the transfer resistance of carriers. The Ni2+ in Ni-MOF provided many cocatalytic sites for H2 evolution via g-C3N4 and CdS. Furthermore, charge carrier separation in Ni-MOF/CN/CdS improved after the innovative addition of MVTh. This study provides a reference for the construction of a closed-loop heterojunction system without precious metal cocatalysts.

Road Map for In Situ Grown Binder-Free MOFs and Their Derivatives as Freestanding Electrodes for Supercapacitors

Among several electrocatalysts for energy storage purposes including supercapacitors, metal-organic frameworks (MOFs), and their derivatives have spurred wide spread interest owing to their structural merits, multifariousness with tailor-made functionalities and tunable pore sizes. The electrochemical performance of supercapacitors can be further enhanced using in situ grown MOFs and their derivatives, eliminating the role of insulating binders whose "dead mass" contribution hampers the device capability otherwise. The expulsion of binders not only ensures better adhesion of catalyst material with the current collector but also facilitates the transport of electron and electrolyte ions and remedy cycle performance deterioration with better chemical stability. This review systematically summarizes different kinds of metal-ligand combinations for in situ grown MOFs and derivatives, preparation techniques, modification strategies, properties, and charge transport mechanisms as freestanding electrode materials in determining the performance of supercapacitors. In the end, the review also highlights potential promises, challenges, and state-of-the-art advancement in the rational design of electrodes to overcome the bottlenecks and to improve the capability of MOFs in energy storage applications.

Incorporation of α-MnO2 Nanoflowers into Zinc-Terephthalate Metal-Organic Frameworks for High-Performance Asymmetric Supercapacitors

Herein, we report the synthesis of α-MnO₂ nanoflower-incorporated zinc-terephthalate MOFs (MnO₂@Zn-MOFs) via the conventional solution phase synthesis technique as an electrode material for supercapacitor applications. The material was characterized by powder-X-ray diffraction, scanning electron microscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy techniques. The prepared electrode material exhibited a specific capacitance of 880.58 F g^-1 at 5 A g^-1, which is higher than the pure Zn-BDC (610.83 F g^-1) and pure α-MnO₂ (541.69 F g^-1). Also, it showed a 94% capacitance retention of its initial value after 10,000 cycles at 10 A g^-1. The improved performance is attributed to the increased number of reactive sites and improved redox activity due to MnO₂ inclusion. Moreover, an asymmetric supercapacitor assembled using MnO₂@Zn-MOF as the anode and carbon black as the cathode delivered a specific capacitance of 160 F g^-1 at 3 A g^-1 with a high energy density of 40.68 W h kg^-1 at a power density of 20.24 kW kg^-1 with an operating potential of 0-1.35 V. The ASC also exhibited a good cycle stability of 90% of its initial capacitance.

Exploring MOF-199 composites as redox-active materials for hybrid battery-supercapacitor devices

Metal-organic frameworks (MOFs) have emerged as intriguing porous materials with diverse potential applications. Herein, we synthesized a copper-based MOF (MOF-199) and investigated its use in energy storage applications. Methods were adapted to intensify the electrochemical characteristics of MOF-199 by preparing composites with graphene and polyaniline (PANI). The specific capacity of the synthesized MOF in a three-electrode assembly was significantly enhanced from 88 C g^-1 to 475 C g^-1 and 766 C g^-1 with the addition of graphene and polyaniline (PANI), respectively. Due to the superior performance of (MOF-199)/PANI, a hybrid supercapacitor was fabricated with the structure of (MOF-199)/PANI//activated carbon, which displayed an excellent maximum energy and power density of 64 W h kg^-1 and 7200 W kg^-1, respectively. The hybrid device exhibited an appreciable capacity retention of 92% after 1000 charge-discharge cycles. Moreover, using Dunn's model, the capacitive and diffusive contributions as well as the k ₁ and k ₂ currents of the fabricated device were calculated, validating the hybrid nature of the supercapattery device. The current studies showed that MOF-199 exhibits promising electrochemical features and can be considered as potential electrode material for hybrid energy storage devices.

Tailoring activation of CoNiO nanoparticles/porous carbon nanofibers by atomic doping for high performance supercapacitors

Metal-organic framework (MOF) materials are rich in active sites and have a high specific surface area, which make them potential electrode materials. In this work, a simple immersion method combined with a carbonization treatment process is applied to prepare MOF derived composite materials (CoNiO/PCNFs). Among them, cobalt-based MOFs (Co-MOFs) are selected as the precursor and doped with Ni atoms, and the ratio of Co and Ni is tailored to acquire a high-performance electrode. The electrochemical results show that when the ratio of Co to Ni is 2 : 2, the prepared CoNiO/PCNFs-2 electrode has high capacitance (912.4 F g^-1 at 1 A g^-1) and superior rate capability (retention is above 50% at 100 A g^-1). Additionally, it is highly stable at 20 A g^-1 (nearly no degradation after 6000 cycles). Density Functional Theory (DFT) calculations indicate that the Ni doping models present lower formation energy and better -OH group adsorption properties. Moreover, the density of electronic state (DOS) and differential charge density distribution demonstrate that Ni doping effectively enhances the charge transport during the charging and discharging processes, which is beneficial to enhance the energy storage of the electrode materials. In conclusion, this work presents a strategy to design MOF-derived composite electrodes. The experimental tests and theoretical calculations explore the energy storage process and prove that the CoNiO/PCNF electrode materials have great potential for applications.

Core-Shell Carbon Nanofibers@Ni(OH)2/NiO Composites for High-Performance Asymmetric Supercapacitors

The application of transition metal oxides/hydroxides in energy storage has long been studied by researchers. In this paper, the core-shell CNFs@Ni(OH)₂/NiO composite electrodes were prepared by calcining carbon nanofibers (CNFs) coated with Ni(OH)₂ under an N₂ atmosphere, in which NiO was generated by the thermal decomposition of Ni(OH)₂. After low-temperature carbonization at 200 °C, 250 °C and 300 °C for 1 h, Ni(OH)₂ or/and NiO existed on the surface of CNFs to form the core-shell composite CNFs@Ni(OH)₂/NiO-X (X = 200, 250, 300), in which CNFs@Ni(OH)₂/NiO-250 had the optimal electrochemical properties due to the coexistence of Ni(OH)₂ and NiO. Its specific capacitance could reach 695 F g^-1 at 1 A g^-1, and it still had 74% capacitance retention and 88% coulomb efficiency after 2000 cycles at 5 A g^-1. Additionally, the asymmetric supercapacitor (ASC) assembled from CNFs@Ni(OH)₂/NiO-250 had excellent energy storage performance with a maximum power density of 4000 W kg^-1 and a maximum functional capacity density of 16.56 Wh kg^-1.

Improved Photocatalytic Activity via n-Type ZnO/p-Type NiO Heterojunctions

The design and construct pn heterojunction to reduce the recombination rate of photogenerated electron-hole pairs can effectively improve photocatalytic activity. In this study, ZnO/NiO heterojunctions were fabricated by annealing a Zn/Ni metal organic framework precursor synthesized via coprecipitation. The effects of the precursor annealing temperature on the microstructure, morphology, and optical properties of the ZnO/NiO nanocomposites were investigated using X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and UV-vis absorption spectroscopy. The results showed that the nanocomposite was composed of hexagonal wurtzite ZnO and cubic NiO, with the former being the dominant phase. Large ZnO nanoparticles were attached to small NiO nanoparticles, and a pn heterojunction interface was formed. The photodegradation performance of the nanomaterials was evaluated by monitoring the degradation of RhB under irradiation by ultraviolet light. The ZnO/NiO nanocomposites exhibited excellent photocatalytic activity when the annealing temperature was 550 °C. The photodegradation mechanism was also analyzed in detail, revealing that the heterojunction between the n-type ZnO and the p-type NiO played an important role in impeding the recombination of photogenerated electron-hole pairs and improving the photocatalytic efficiency.

Three-dimensional Ni4O4-cubane metal-organic framework as a high-performance electrocatalyst for urea oxidation

The urea oxidation reaction (UOR) is considered to be a replacement of the sluggish anodic oxygen evolution reaction (OER) in overall water-splitting. A three-dimensional (3D) nickel-containing metal-organic framework {[NiII 2(pdaa)(OH)2(H2O)] n (MOF 1) (where, H2pdaa = 1,4-phenylene diacetic acid) was investigated as a robust and highly efficient electrocatalyst for the UOR. MOF 1 comprised 1D nickel(ii) chains crosslinked through Ni4O4 cubane units to form a 3D extended network. Dangling Ni⋯OH- groups were exposed in the MOF 1 structure, and could act as active catalytic centers for the UOR. MOF 1 required a very small onset potential of 1.18 V for urea oxidation in KOH (1 M) and urea (0.33 M) and had a low Tafel slope of 38.8 mV dec-1 (in contrast to 1.84 V for the oxygen evolution reaction). The overpotential required to attain a catalytic current density of 10 mA cm-2 was 1.24 V, which is much lower than that for many materials. Controlled potential electrolysis, powder X-ray diffraction, and X-ray photoelectron spectroscopy affirmed the physicochemical integrity of the catalyst over a 17 h test reaction. This work not only addresses the problem of urea contamination, it also helps to utilize it in an energy-conversion process.

Metal-Organic Framework Materials for Electrochemical Supercapacitors

Exploring new materials with high stability and capacity is full of challenges in sustainable energy conversion and storage systems. Metal-organic frameworks (MOFs), as a new type of porous material, show the advantages of large specific surface area, high porosity, low density, and adjustable pore size, exhibiting a broad application prospect in the field of electrocatalytic reactions, batteries, particularly in the field of supercapacitors. This comprehensive review outlines the recent progress in synthetic methods and electrochemical performances of MOF materials, as well as their applications in supercapacitors. Additionally, the superiorities of MOFs-related materials are highlighted, while major challenges or opportunities for future research on them for electrochemical supercapacitors have been discussed and displayed, along with extensive experimental experiences.

In-Built Fabrication of MOF Assimilated Porous Hollow Carbon from Pre-Hydrolysate for Supercapacitor

With the fast consumption of traditional fossil fuels and the urgent requirement for a low-carbon economy and sustainable development, supercapacitors are gaining more and more attention as a clean energy storage and conversion device. The research on electrode materials for supercapacitors has become a hot topic nowadays. An electrode material for a supercapacitor, comprising the ZIF-67 in-built carbon-based material, was prepared from a biomass pre-hydrolysate via a hydrothermal process. As a by-product of dissolving slurry, the pre-hydrolysate is rich in carbon, which is an excellent biomass resource. The utilization of pre-hydrolysate to prepare carbon energy materials could realize the high value utilization of pre-hydrolysate and the efficient energy conversion of biomass. Meanwhile, the cobalt-based MOF (such as ZIF-67), as a porous crystalline material, has the advantages of having a regular order, high specific surface area and controllable pore size, as well as good thermal and chemical stability. The addition of ZIF-67 modified the morphology and pore structure of the carbon, and the obtained samples showed outstanding electrochemical performance. One- and two-step synthetic processes generated specimens with a coral-like cross-linked structure and a new type of rough, hollow, dandelion-like structure, respectively, and the pore size was in the range of 2.0–5.0 nm, which is conducive to ion transport and charge transfer. In C2-ZIF-67, the hollow structures could effectively prevent the accumulation of the electrochemical active center, which could provide enough space for the shrinkage and expansion of particles to protect them from the interference of electrolytes and the formation of solid electrolyte interphase film layers. Additionally, the plush tentacle structure with low density and a large specific surface area could expose more active sites and a large electrolyte electrode contact area, and short electron and charge transport paths. Importantly, active, free electrons of small amounts of Co-MOF (1 wt%) could be stored and released through the redox reaction, further improving the electrical conductivity of Carbon-ZIF-67 materials in this work. Consequently, C2-ZIF-67 exhibited superior specific capacitance (400 F g⁻¹, at 0.5 A g⁻¹) and stability (90%, after 10,000 cycles).

Hierarchical nickel oxalate superstructure assembled from 1D nanorods for aqueous Nickel-Zinc battery

Hierarchical superstructures in nano/microsize can provide improved transport of ions, large surface area, and highly robust structure for electrochemical applications. Herein, a facile solution precipitation method is presented for synthesizing a hierarchical nickel oxalate (Ni-OA) superstructure composed of 1D nanorods under the control of mixed solvent and surfactant of sodium dodecyl sulfate (SDS). The growth process of the hierarchical Ni-OA superstructure was studied and indicated that the product had good stability in mixed solvent. Owing to smaller size, shorter pathway of ion diffusion, and abundant interfacial contact with electrolytes, hierarchical Ni-OA superstructure (Ni-OA-3) showed higher specific capacity than aggregated micro-cuboids (Ni-OA-1) and self-assembled micro/nanorods (Ni-OA-2). Moreover, the assembled Ni-OA-3//Zn battery showed good cyclic stability in aqueous electrolytes, and achieved a maximum energy density of 0.42 mWh cm^-2 (138.75 Wh kg^-1), and a peak power density of 5.36 mW cm^-2 (1.79 kW kg^-1). This work may provide a new idea for the investigation of hierarchical nickel oxalate-based materials for electrochemical energy storage.

NiO-Based Electronic Flexible Devices

Personal, portable, and wearable electronics have become items of extensive use in daily life. Their fabrication requires flexible electronic components with high storage capability or with continuous power supplies (such as solar cells). In addition, formerly rigid tools such as electrochromic windows find new utilizations if they are fabricated with flexible characteristics. Flexibility and performances are determined by the material composition and fabrication procedures. In this regard, low-cost, easy-to-handle materials and processes are an asset in the overall production processes and items fruition. In the present mini-review, the most recent approaches are described in the production of flexible electronic devices based on NiO as low-cost material enhancing the overall performances. In particular, flexible NiO-based all-solid-state supercapacitors, electrodes electrochromic devices, temperature devices, and ReRAM are discussed, thus showing the potential of NiO as material for future developments in opto-electronic devices.

Electrochemical deposition of ZnCo2O4/NiCo2S4 nanosheet arrays for high-performance supercapacitors

ZnCo2O4/NiCo2S4 composites were deposited on carbon cloth for high-performance supercapacitors by electrochemical deposition using a mixed solution of MOF-drived ZnCo2O4 nanoclusters and Ni, Co, S sources.

Self-templating Scheme for the Synthesis of NiCo2Se4 and BiSe Hollow Microspheres for High-energy Density Asymmetric Supercapacitors

Porous hollow structure of the electrode materials can enlarge the surface area in contact with the electrolyte, accelerating the transport of ions and electrons during redox reaction to enhance electrochemical...

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.

Hetero-architectured core-shell NiMoO4@Ni9S8/MoS2 nanorods enabling high-performance supercapacitors

ABSTRACT

An effective technique for improving electrochemical efficiency is to rationally design hierarchical nanostructures that completely optimize the advantages of single components and establish an interfacial effect between structures. In this study, core-shell NiMoO₄@Ni₉S₈/MoS₂ hetero-structured nanorods are prepared via a facile hydrothermal process followed by a direct sulfurization. The resulting hierarchical architecture with outer Ni₉S₈/MoS₂ nanoflakes shell on the inner NiMoO₄ core offers plentiful active sites and ample charge transfer pathways in continuous heterointerfaces. Ascribing to the porous core-shell configuration and synergistic effect of bimetal sulfides, the obtained NiMoO₄@Ni₉S₈/MoS₂ as electrode material presents an unsurpassed specific capacity of 373.4 F g^-1 at 10 A g^-1 and remarkable cycling performance in the 6 M KOH electrolyte. This work delivers a rational method for designing highly efficient electrodes for supercapacitors, enlightening the road of exploring low-cost materials in the energy storage domain.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1557/s43578-021-00318-y.

The intergrated nanostructure of bimetallic CoNi-based zeolitic imidazolate framework and carbon nanotubes as high-performance electrochemical supercapacitors

In this study, a series of one-dimensional (1D)/two-dimensional (2D) heterostructure hybrids were fabricated through the in situ growth of a Co and Ni bimetallic zeolitic imidazolate framework (CoNi-ZIF) around N-doped carbon nanotubes (N-CNTs). The hybrids were further exploited as effective supercapacitor materials. The N-CNTs were prepared by carbonizing a mixture of glucose and the melamine-cyanuric acid complex at a high temperature (900 °C) under N₂ atmosphere and applied as the template for the in situ synthesis of CoNi-ZIF nanosheets (NSs). The 1D N-CNTs in the hybrids can act as the high-way for charge transfer to boost the faradaic reactions. Changing the usage of metal precursors not only provided abundant redox reaction sites in 2D CoNi-ZIF NSs but also modulated the microstructures and chemical components of the hybrids. The integration of the features of N-CNTs and CoNi-ZIF NSs can result in a synergistic effect between N-CNTs and CoNi-ZIF NSs. Therefore, the obtained CoNi-ZIFs and N-CNTs hybrid (CoNi-ZIF@N-CNT) exhibited superior electrochemical capacitive performance. Comparison revealed that the CoNi-ZIF@N-CNT-2 hybrid, which was prepared with a 1:1 mass ratio of Co(NO₃)₂·6H₂O and Ni(NO₃)₂·6H₂O, displayed the largest specific capacitance of 1118F g^-1 at 1 A g^-1, which was higher than the capacitance of most reported metal-organic framework (MOF)-based supercapacitor electrodes. Moreover, the asymmetric supercapacitor based on the CoNi-ZIF@N-CNT-2 electrode exhibited a high energy density of 51.1 Wh kg^-1 at the power density of 860.1 W kg^-1 and good cycle stability. This work can provide a facile and effective way for the fabrication of heterostructured 1D/2D nanostructures based on 2D MOFs for advanced energy storage.

Plant polyphenols induced the synthesis of rich oxygen vacancies Co3O4/Co@N-doped carbon hollow nanomaterials for electrochemical energy storage and conversion

Reasonable hollow structure design and oxygen vacancy defects control play an important role in the optimization of electrochemical energy storage and electrocatalytic properties. Herein, a plant polyphenol tannic acid was used to etch Co-based zeolitic imidazolate framework (ZIF-67) followed by calcination to prepare a porous Co₃O₄@Co/NC hollow nanoparticles (Co₃O₄@Co/NC-HN) with rich oxygen vacancy defects. Owing to the metal-phenolic networks (MPNs), rich oxygen vacancy defects and the synergistic effect between Co₃O₄ and Co/NC, the box-like Co₃O₄@Co/NC-HN nanomaterials with large specific surface areas exhibit excellent supercapacitor performance and electrocatalytic activity. As expected, Co₃O₄@Co/NC-HN shows high specific capacity (273.9 mAh g^-1 at 1 A g^-1) and remarkable rate performance. Moreover, the assembled Hybrid supercapacitor (HSC, Co₃O₄@Co/NC-HN//Active carbon) device obtained a maximum energy density of 57.8 Wh kg^-1 (800 W kg^-1) and exhibited superior cycle stability of 92.6% after 4000 cycles. Notably, as an electrocatalyst, the nanocomposites exhibit small overpotential and Tafel slope. These results strongly demonstrate that both unique hollow structure and abundant oxygen vacancies designed from plant polyphenols provide superiorities for the synthesis of efficient and green multifunctional electrode materials for energy storage and conversion.

An iron based organic framework coated with nickel hydroxide for energy storage, conversion and detection

Although electrode materials based on metal organic frameworks (MOFs) were widely studied in the electrochemistry field, the origin of poor conductivity is still a bottleneck restricting their development. Herein, we constructed a conductive circuit by growing a layer of hydroxide on the surface of the Fe-MOF, and composite materials (Fe-MOF@Ni(OH)₂) are applied in the fields of supercapacitor, OER, and electrochemical sensing. Fe-MOF@Ni(OH)₂ not only maintains the intrinsic advantages of Fe-MOF, but also improves the electrical conductivity. Fe-MOF@Ni(OH)₂ exhibits a high specific capacity of 188 mAh g^-1 at 1 A g^-1 . The energy density of the asymmetric supercapacitor (Fe-MOF@Ni(OH)₂-20//AC) reaches 67.1 Wh kg^-1. During the oxygen evolution reaction, the overpotential of the material is 280 mV at 10 mA cm^-2, and the Tafel slope is 37.6 mV dec^-1. The electrochemical sensing tests showed the detection limit of BPA is 5 μM. Hence, these results provide key insights into the design of multifunctional electrode materials.

Fabrication of Nanoflower-like MCoP (M = Fe and Ni) Composites for High-Performance Supercapacitors

Elaborating the development of functional materials with excellent performance for supercapacitors is important in energy storage devices. In the present study, nanoflower-like MCoP (M = Ni and Fe) composites were successfully fabricated on Ni foam (denoted as NF@MCoP) by a cost-effective hydrothermal and low-temperature phosphating method. Simultaneously, the unique three-dimensional structure, nanoflower morphology, and the conductive substrate provide a favorable large electroactive area, shorter electron transfer distance, and rapid electron conductivity. The as-synthesized nanoflower-like MCoP composites exhibit outstanding energy density, power density, and long-term cycling stability. These results show that the developed electrode materials with excellent performance have great application prospects in the field of supercapacitor applications.