Nanosheet-assembled porous MnCo2O4.5 microflowers as electrode material for hybrid supercapacitors and lithium-ion batteries

Bimetal-organic frameworks derived redox-type composite materials for high-performance energy storage

Electrodes and electroactive materials are crucial components in the development of supercapacitors due to their geometric properties. In this study, bimetal-organic frameworks (Bi-MOFs, ZIF-8@ZIF-67) were utilized as electrode materials for a high-performance hybrid supercapacitor (HSC) by designing a novel synthesis of metallic carbonate hydroxide/oxides. In particular, the Bi-MOFs function as a sacrificial precursor in the synthesis of hollow NiMn(CO3)0.5·0·.11H2O/ZnO@Co3O4 CNCs (NM-CH/ZnO@Co3O4 CNCs) cubic composite materials by a straightforward low-temperature treatment. The NM-CH/ZnO@Co3O4 CNCs exhibited exceptional electrochemical performance with high specific capacity of 196.3 ± 0.08 mAh/g, specific capacitance of 1179 ± 0.10 F g-1 at 0.5 A g-1, and outstanding cycling stability of 98% after 25,000 cycles compared to the other electrode materials. The porous and hollow structure, along with a large surface area, contributed to the enhanced electrochemical properties of the composite material. An HSC was constructed using NM-CH/ZnO@Co3O4 CNCs as the cathode and activated porous carbon (APC) as the anode, resulting in a device with a specific energy of 33 ± 0.12 Wh kg-1 and a power density of 19354 ± 0.07 W kg-1. The use of Bi-MOF electrodes presents new avenues for the development of high-performance energy storage materials, with the potential for industrial energy storage application demonstrated though the successful powering of portable lightbulbs.

Evaluation of the effect of precursor ratios on the electrochemical performances of binder-free NiMn-phosphate electrodes for supercapattery

Binary metal phosphate electrodes have been widely studied for energy storage applications due to the synergistic effects of two different transition elements that able to provide better conductivity and stability. Herein, the battery-type binder-free nickel-manganese phosphate (NiMn-phosphate) electrodes were fabricated with different Ni:Mn precursor ratios via microwave-assisted hydrothermal technique for 5 min at 90 °C. Overall, NiMn3P electrode (Ni:Mn = 1:3) showed an outstanding electrochemical performance, displaying the highest specific (areal) capacity at 3 A/g of 1262.4 C/g (0.44 C/cm2), and the smallest charge transfer resistance of 108.8 Ω. The enhanced performance of NiMn3P electrode can be ascribed to the fully grown amorphous nature and small-sized flake and flower structures of NiMn3P electrode material on the nickel foam (NF) surface. This configuration offered a higher number of active sites and a larger exposed area, facilitating efficient electrochemical reactions with the electrolyte. Consequently, the NiMn3P//AC electrode combination was chosen to further investigate its performance in supercapattery. The NiMn3P//AC supercapattery exhibited remarkable energy density of 105.4 Wh/kg and excellent cyclic stability with 84.7% retention after 3000 cycles. These findings underscored the superior electrochemical performance of the battery-type binder-free NiMn3P electrode, and highlight its potential for enhancing the overall performance of supercapattery.

Fabrication of Ni-Polyaniline/Graphene Oxide Composite Electrode with High Capacitance and Water Splitting Activity

The Ni-PANI@GO composite electrode was fabricated via cost effective electrodeposition technique. According to the XRD, FTIR, Raman, SEM, and XPS analyses revealed that the nickel doped PANI@GO composite has been fabricated on the surface of the nickel foam. Addition of nickel significantly enhanced interaction between graphene with PANI leading to higher degree of polyaniline doping though imine groups. Electrochemical investigation revelated the significant performance of the Ni-PANI@GO composite electrode, boosting an impressive capacitance of 4480 F/g at 40 A/g, surpassing previous Ni-foam-based binder-free electrodes. Notably, Ni-PANI@GO electrode displayed excellent catalytic activity in both oxygen evolution reaction (OER) and hydrogen evolution reaction (HER), generating a considerable volume of the gas bubbles at relatively modest overpotentials of 279 mV and 244 mV respectively. This event allows for the achievement of 20 mA cm-2 current density. Furthermore, in the laboratory-scale water electrolyzer, a low cell voltage of 1.72 V was achieved, facilitating a water-splitting current density of 20 mA cm-2. This study underscores the premising potential for the real-world device's application of the versatile Ni-PANI@GO composite electrode.

Development of lignin hydrogel reinforced polypyrrole rich electrode material for supercapacitor and sensing applications

The preparation of natural polymer-based highly conductive hydrogels with reliable durability for applications in supercapacitors (SCs) is still challenging. Herein, a facile method to prepare alkaline lignin (AL)-based polypyrrole (PPy)-rich, high-conductive PPy@AL/PEGDGE gel was reported, where AL was used as a dopant, polyethylene glycol diglycidyl ether (PEGDGE) as a cross-linking agent, and PPy as a conducting polymer. The PPy@AL/PEGDGE gel electrode materials with hollow structures were prepared by electrochemical deposition and chemical etching method and then assembled into sandwich-shaped SCs. Cyclic voltammetry (CV), galvanotactic charge discharge (GCD), electrochemical impedance spectroscopy (EIS) and cycling stability tests of the PPy@AL/PEGDGE SCs were performed. The results demonstrated that the SCs can achieve a conductivity of 25.9 S·m-1 and a specific capacitance of 175 F·g-1, which was 127.4 % higher compared to pure PPy (77 F·g-1) electrode. The highest energy density and power density for the SCs were obtained at 23.06 Wh·kg-1 and 5376 W·kg-1, respectively. In addition, the cycling performance was also higher than that of pure PPy assembled SCs (50 %), and the capacitance retention rate can reach 72.3 % after 1000 cycles. The electrode materials are expected to be used as sensor and SCs devices.

Porous and graphitic carbon nanosheets with controllable structure for zinc-ion hybrid capacitor

The imbalances of storage capacity and reaction kinetics between carbonaceous cathodes and zinc (Zn) anodes restrict the widespread application of Zn-ion hybrid capacitor (ZIHC). Structure optimization is a promising strategy for carbon materials to achieve sufficient Zn2+ storage sites and satisfied ion-electron kinetics. Herein, porous graphitic carbon nanosheets (PGCN) were simply synthesized using a K3[Fe(C2O4)3]- and urea-assisted foaming strategy with polyvinylpyrrolidone as carbon precursor, followed by activation and graphitization. Sufficient pores with well-matched pore sizes (0.80-1.94 nm) distributed across the carbon nanosheets can effectively shorten mass-transfer distance, promoting accessibility to active sites. A partially graphitic carbon structure with high graphitization degree can accelerate electron transfer. Furthermore, high nitrogen doping (7.2 at.%) provides additional Zn2+ storage sites to increase storage capacity. Consequently, a PGCN-based ZIHC has an exceptional specific capacity of 181 mAh g-1 at 0.5 A g-1, superb energy density of 145 Wh kg-1, and excellent cycling ability without capacity decay over 10,000 cycles. In addition, the flexible solid-state device assembled with PGCN exhibits excellent electrochemical performances even when bent at various angles. This study proposes a straightforward and economical strategy to construct porous graphitic carbon nanosheets with enhanced storage capacity and fast reaction kinetics for the high performance of ZIHC.

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.

Boosting the Electrochemical Storage Properties of Co3O4 Nanowires by the Mn Doping Strategy with Appropriate Mn Doping Concentrations

High specific capacitance, high energy density, and high power density have always been important directions for the improvement of electrode materials for supercapacitors. In this paper, Co3O4 nanowire arrays with various Mn doping concentrations (Mn:Co molar ratio = 1:11, 1:5, 1:2) directly grown on nickel foam (NF) were prepared by a simple hydrothermal method and annealing process. The influence of Mn doping on the morphology, structure, and electrochemical behaviors of Co3O4 was investigated. The results show that partial substitution of Co ions with Mn ions in the spinel structure does not change the nanowire morphology of pure Co3O4 but increases the lattice parameter and decreases the crystallinity of cobalt oxide. Electrochemical measurements showed that Mn doping in Co3O4 could effectively enhance the redox activity, especially Co3O4 with a Mn doping ratio of 1:5, which exhibits the most excellent electrochemical performance, with the maximum specific capacitance of 1210.8 F·g-1 at 1 A·g-1 and a rate capability of 33.0% at 30 A·g-1. The asymmetric supercapacitor (ASC) device assembled with the optimal Mn-Co3O4 (1:5) and activated carbon (AC) electrode performs a high specific capacitance of 105.8 F·g-1, a high energy density of 33 Wh·kg-1 at a power density of 748.1 W·kg-1, and a capacitance retention of 60.2% after 5000 cycles. This work indicates that an appropriate Mn doping concentration in the Co3O4 lattice structure will have great potential in rationalizing the design of spinel oxides for efficient electrochemical performance.

Hierarchically crystalline copper borate nanosheets as a freestanding electrode for a hybrid supercapacitor

In this study, we have suggested a straightforward approach to fabricating a binder-free electrode of hierarchically crystalline copper borate (Cu-Bi) nanosheets grown on nickel foam using the Successive Ionic Layer Adsorption Reaction (SILAR) method. The best-performing electrode shows a remarkable specific capacitance (Cs) of 2002 Fg-1 at 1 Ag-1 and Cs retention of 85 % for 10,000 GCD cycles. The assembled CB/NF-2//AC device exhibits high cycling stability and achieves a high energy of 52.2 Whkg-1 at a power density of 2622.4 Wkg-1. Remarkably, it reached 152.7 Fg-1 at 2 Ag-1, and the device still has a high capacitance retention of 85 % for 10,000 cycles. This remarkable electrochemical activity could be attributed to: (i) the inherent defects of the prepared electrode via the existence of borates, providing straightforward interaction between the electrolyte and the active species; (ii) designing the hierarchical architecture that could provide a porous nanosheet structure, which generates accessible active sites for quick ion transport, boosting the Cs; (iii) the formation of crystalline Cu-Bi nanosheets, resulting in high stability and superior electrochemical performance compared to the previous amorphous borides; and (iv) the hybridization between the B 2p state and the multiple d-orbitals of transition metals, increasing the electron flow between the atoms. The current work suggests that the growth of hierarchically crystalline Cu-Bi on Ni foam using a low-cost and simple procedure could provide a practical approach to designing hybrid supercapacitors with outstanding electrochemical performance.

Controllable synthesis of Fe3C-reinforced petal-like lignin microspheres with boosted electrochemical performance and its application in high performance supercapacitors

One more effective measure to solve the energy crisis caused by the shortage of fossil energy is to convert natural renewable resources into high-value chemical products for electrochemical energy storage. Lignin has broad application prospects in this field. In this paper, three kinds of lignin with different molecular weights were obtained by the ethanol/water grading of Kraft lignin (KL). Then, different surface morphology lignin microspheres were prepared by spray drying. Finally, petal-like microspheres were successfully prepared by mixing and grinding the above four kinds of surface morphology lignin microspheres with potassium ferrate and cyanogen chloride and carbonizing at 800 °C and were later used as electrode materials for supercapacitors. Compared with the other microspheres, LMS-F3@Fe3C has the highest specific surface area (1041.42 m2 g-1), the smallest pore size (2.36 nm) and the largest degree of graphitization (ID/IG = 1.06). At a current density of 1 A g-1, the maximum specific capacitance is 786.7 F g-1. At a power density of 1000 W kg-1, the high energy density of 83.3 Wh kg-1 is displayed. This work provides a novel approach to the modulation of surface morphology and structure of lignin microspheres.

Advances in Electrospun Materials and Methods for Li-Ion Batteries

Electronic devices commonly use rechargeable Li-ion batteries due to their potency, manufacturing effectiveness, and affordability. Electrospinning technology offers nanofibers with improved mechanical strength, quick ion transport, and ease of production, which makes it an attractive alternative to traditional methods. This review covers recent morphology-varied nanofibers and examines emerging nanofiber manufacturing methods and materials for battery tech advancement. The electrospinning technique can be used to generate nanofibers for battery separators, the electrodes with the advent of flame-resistant core-shell nanofibers. This review also identifies potential applications for recycled waste and biomass materials to increase the sustainability of the electrospinning process. Overall, this review provides insights into current developments in electrospinning for batteries and highlights the commercialization potential of the field.

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.

Coupling W18 O49 /Ti3 C2 Tx MXene Pseudocapacitive Electrodes with Redox Electrolytes to Construct High-Performance Asymmetric Supercapacitors

A pseudocapacitive electrode with a large surface area is critical for the construction of a high-performance supercapacitor. A 3D and interconnected network composed of W₁₈ O₄₉ nanoflowers and Ti₃ C₂ T_x MXene nanosheets is thus synthesized using an electrostatic attraction strategy. This composite effectively prevents the restacking of Ti₃ C₂ T_x MXene nanosheets and meanwhile sufficiently exposes electrochemically active sites of W₁₈ O₄₉ nanoflowers. Namely, this self-assembled composite owns abundant oxygen vacancies from W₁₈ O₄₉ nanoflowers and enough active sites from Ti₃ C₂ T_x MXene nanosheets. As a pseudocapacitive electrode, it shows a big specific capacitance, superior rate capability and good cycle stability. A quasi-solid-state asymmetric supercapacitor (ASC) is then fabricated using this pseudocapacitive anode and the cathode of activated carbon coupled with a redox electrolyte of FeBr₃ . This ASC displays a cell voltage of 1.8 V, a capacitance of 101 F g^-1 at a current density of 1 A g^-1 , a maximum energy density of 45.4 Wh kg^-1 at a power density of 900 W kg^-1 , and a maximum power density of 18 000 W kg^-1 at an energy density of 10.8 Wh kg^-1 . The proposed strategies are promising to synthesize different pseudocapacitive electrodes as well as to fabricate high-performance supercapacitor devices.

A Review on the Application of Cobalt-Based Nanomaterials in Supercapacitors

Among many electrode materials, cobalt-based nanomaterials are widely used in supercapacitors because of their high natural abundance, good electrical conductivity, and high specific capacitance. However, there are still some difficulties to overcome, including poor structural stability and low power density. This paper summarizes the research progress of cobalt-based nanomaterials (cobalt oxide, cobalt hydroxide, cobalt-containing ternary metal oxides, etc.) as electrode materials for supercapacitors in recent years and discusses the preparation methods and properties of the materials. Notably, the focus of this paper is on the strategies to improve the electrochemical properties of these materials. We show that the performance of cobalt-based nanomaterials can be improved by designing their morphologies and, among the many morphologies, the mesoporous structure plays a major role. This is because mesoporous structures can mitigate volume changes and improve the performance of pseudo capacitance. This review is dedicated to the study of several cobalt-based nanomaterials in supercapacitors, and we hope that future scholars will make new breakthroughs in morphology design.