Three-Dimensional Hierarchical Structure ZnO@C@NiO on Carbon Cloth for Asymmetric Supercapacitor with Enhanced Cycle Stability

Hierarchical nanoporous NiCoN nanoflowers with highly rough surface electrode material for high-performance asymmetric supercapacitors

This study presents a novel strategy to enhance the energy storage performance of asymmetric supercapacitors (ASCs) by utilizing nanoporous NiCoN flower structures as the positive electrode material. The NiCoN material is synthesized via a straightforward hydrothermal method, followed by calcination in a nitrogen atmosphere. The resulting electrode demonstrates exceptional electrochemical properties, including a high specific capacity of 773 C g-1 (1955 F g-1), excellent rate capability, and outstanding cycling stability. The hierarchical architecture of the NiCoN electrode, composed of interconnected porous nanosheets, facilitates efficient charge transfer and enhanced electrolyte ion diffusion. When paired with activated carbon (AC) as the negative electrode in the NiCoN//AC ASC configuration, the device achieves an impressive energy density of 36 W h kg-1 at a power density of 775 W kg-1. Moreover, the device exhibits remarkable cycling stability, retaining 85% of its initial capacitance after 5000 charge-discharge cycles. These findings underscore the potential of NiCoN as a high-performance electrode material for ASCs, offering a promising pathway for advancements in next-generation energy storage technologies.

Synergistic effects of hierarchical micro/nanostructures and PDMS/lubricant composites for superior tribological and wetting performance on aluminum

In this study, we propose a method to enhance the friction and wetting properties of aluminum surfaces with micro-/nanostructures by coating them with a PDMS/lubricant composite. Hierarchical micro/nanostructures were formed on the aluminum surface through an etching process, and coating solutions were prepared by mixing xylene and the PDMS/lubricant composites in various ratios. The surface morphology, roughness, and wettability of the coated specimens were analyzed, and their friction and wear characteristics were evaluated under dry and lubricated conditions. The results showed that the PDMS/lubricant composite coating significantly reduced friction and wear under both dry and lubricated conditions owing to the formation of a stable lubricating film. Additionally, the hierarchical micro/nanostructures formed by the etching process improved hydrophobicity and self-cleaning ability. The coated surface exhibited selective wettability towards water and oil, offering various advantages such as prevention of contamination, prevention of wear and performance degradation caused by lubricant oxidation, and enhanced corrosion resistance. The findings of this study are expected to contribute to the development of lightweight mechanical-component technologies with improved durability and wear resistance.

Recent Development on Transition Metal Oxides-Based Core-Shell Structures for Boosted Energy Density Supercapacitors

In recent years, nanomaterials exploration and synthesis have played a crucial role in advancing energy storage research, particularly in supercapacitor development. Researchers have diversified materials, including metal oxides, chalcogenides, and composites, as well as carbon materials, to enhance energy and power density. Balancing energy density with electrochemical stability remains challenging, driving intensified efforts in advancing electrode materials. This review focuses on recent progress in designing and synthesizing core-shell materials tailored for supercapacitors. The core-shell architecture offers advantages such as increased surface area, redox active sites, electrical conductivity, ion diffusion kinetics, specific capacitance, and cyclability. The review explores the impact of core and shell materials, specifically transition metal oxides (TMOs), on supercapacitor electrochemical behavior. Metal oxide choices, such as cobalt oxide as a preferred core and manganese oxide as a shell, are discussed. The review also highlights characterization techniques for assessing structural, morphological, and electrochemical properties of core-shell materials. Overall, it provides a comprehensive overview of ongoing TMOs-based core-shell material research for supercapacitors, showcasing their potential to enhance energy storage for applications ranging from gadgets to electric vehicles. The review outlines existing challenges and future opportunities in evolving TMOs-based core-shell materials for supercapacitor advancements, holding promise for high-efficiency energy storage devices.

Temperature-Dependent Electrochemical Performance of Ta-Substituted SrCoO3 Perovskite for Supercapacitors

Developing new electrode materials with good temperature-dependent electrochemical performance has become a great issue for the deployment of hybrid supercapacitors with wide temperature tolerance. In this work, a series of Ta-substituted SrCo1-x Tax O3-δ (x=0.05, 0.10, 0.15, 0.20) perovskites have been studied as positive electrodes for hybrid supercapacitors in terms of their structures, elemental valence states and electrochemical performances. Incorporating Ta into SrCoO3-δ perovskite not only stabilizes the crystallite structure but also notably improves electrochemical activities. The SrCo0.95 Ta0.05 O3-δ @CC delivers the highest specific capacity (Qsp ) of 227.91 C g-1 at 1 A g-1 , which is attributed to the highest oxygen vacancy content and the fastest oxygen diffusion kinetics. The hybrid supercapacitor SrCo0.95 Ta0.05 O3-δ @CC//AC@CC exhibits a high energy density of 22.82 Wh kg-1 @775.09 W kg-1 and a stable long-term cycle life (5000 cycles) with 90.7 % capacity retention. As temperature increases from 25 to 85 °C, the capacitance properties are improved at elevated temperatures for both electrode and device due to the increased electrolyte conductivity. The outstanding electrochemical results present that SrCo1-x Tax O3-δ perovskite holds good prospects for hybrid supercapacitors with wide temperature tolerance.

N-doped CNTs wrapped sulfur-loaded hierarchical porous carbon cathode for Li-sulfur battery studies

Lithium-sulfur (Li-S) batteries are considered promising next-generation energy storage devices due to their low cost and high energy density (2600 W h kg-1). However, the practical applicability of Li-S batteries is hindered by the insulating nature of sulfur cathodes, and the high solubility of polysulfides (Li2Sx, 3 < x ≤ 8) which are formed during the electrochemical process. Integrating sulfur into the carbon host is an effective way to enhance the conductivity of the electrode which hampers the shuttling effect of the polysulfides. Here in this study, hierarchical porous carbon structures (HPC) are prepared from spent coffee waste (SCW) by the KOH activation process and are encapsulated with sulfur (SHPC) which increases the interaction between sulfur and carbon and enhances both the electronic and ionic conductivities. Further wrapping of SHPC with N-doped multi-walled carbon nanotubes (NCNTs) gives a SHPC-NCNT composite, which alleviates the shuttling of polysulfides by trapping them and ensures the required conductivity to the sulfur cathode during the Li+ reactions. When studied as a cathode material for Li-S batteries, the prepared cathode showed 664 and 532 mA h g-1 specific capacities after 150 cycles at 0.2C and 0.5C, respectively. The stable cyclability and rate capability properties of SPHCNCNT suggest that the prepared sulfur composite is suitable as a cathode material for Li+ energy storage applications.

Magnetic Ni@C nanoadsorbents for methyl orange removal from water

In this study, Ni@C nanoparticles were produced and used as an adsorbent for removing methyl orange (MO) from an aqueous solution. The sol-gel method was utilized for the preparation of the particles. The X-ray diffraction pattern and transmission electron microscopy (TEM) were utilized to determine the phase, morphology, and size. The electron micrograph indicated the coating of carbon over Ni having size between 43 and 94 nm, and the Raman spectrum supported it. Among three, the maximum specific magnetization of the Ni@C nanocomposite was 55.78 emu/g for the N7 sample. From the BET approach, specific surface areas of 2.29 × 105, 3.66 × 105, and 5.48 × 105 cm2/g as well as average pore size of 49.30, 37.25, and 35.27 nm were observed for N5, N6, and N7, respectively. The Ni@C nanoparticles were magnetically separable and exhibited rapid adsorption of MO of different concentrations from their aqueous solutions. The N7 adsorbent displayed the highest MO adsorption capacity (~ 32 mg·g-1) along with maintaining an adsorption capacity of 81% even after 5 cycles. Adsorption isotherm and kinetic analysis gave critical inputs toward the possible adsorption mechanism.

Enhancing electrochemical nitrite sensing with a novel nanocomposite of activated carbon/carbon cloth derived from microbial biofilm

A novel approach was employed to fabricate a biofilm-derived activated carbon (BioAc) electrode on a carbon cloth (Cc) substrate for electrochemical nitrite sensing in water samples. The biofilm/Cc electrode was developed using a bioelectrochemical reactor, featuring a three-electrode system with nutrient media and microbial sources. The resultant biofilm electrode was activated at 450 °C for 2 h to eliminate impurities and enhance porosity. Morphological analysis of the BioAc/Cc electrode revealed a surface characterized by a compact film composed of numerous carbon nanoparticles. X-ray diffraction (XRD) analysis exhibited broad, highly crystalline peaks, enhancing both the electrode surface area and conductivity. Amperometry tests on the modified BioAc/Cc electrodes demonstrated a detection limit of 0.015 μM, a sensitivity of 1946.54 μA mM-1 cm-2, and a linear range spanning 0.35-478.21 μM at neutral pH conditions. Moreover, the electrodes demonstrated good stability with a RSD of 2.25% after 60 days and high reproducibility with an RSD of 1.64%. Real-time results showed 99.2 and 100.1% recovery for tap water and drinking water, respectively, highlighting the potential for commercialization in the future. These findings suggest that the BioAc/Cc electrode holds substantial potential for precise nitrite detection in environmental and wastewater applications.

Fabrication of Nitrogen-Doped Carbon-Coated NiS1.97 Quantum Dots for Advanced Magnesium-Ion Batteries

Magnesium (Mg) batteries have garnered considerable interest because of their safety characteristics and low costs. However, the practical application of Mg batteries is hindered by the slow diffusion of Mg ions in the cathode materials. In this study, we prepared NiS1.97 quantum dot composites with nitrogen doping and carbon coating (NiS1.97 QDs@NC) using a one-step sulfurization process with NiO QDs/Ni@NC as the precursor. We applied the prepared NiS1.97 QDs/Ni@NC-based cathodes to Mg batteries because of the large surface area of the quantum dot composite, which provided abundant intercalation sites. This design ensured efficient deintercalation of magnesium ions during charge-discharge processes. The fabricated NiS1.97 QDs@NC displayed a high reversible Mg storage capacity of 259.1 mAh g-1 at 100 mA g-1 and a good rate performance of 96.0 mAh g-1 at 1000 mA g-1. Quantum dot composites with large surface areas provide numerous embedded sites, which ensure effective deintercalation of Mg ions during cycling. Thus, the proposed cathode synthesis strategy is promising for Mg-ion-based energy storage systems.

Solvent-Controlled Morphology of Zinc-Cobalt Bimetallic Sulfides for Supercapacitors

Bimetallic sulfides offer high theoretical specific capacitance and good stability as electrode materials due to their diverse redox reactions, larger specific surface areas, and better conductivity. The morphology of the electrode material is an important influencing factor for the electrochemical properties. Herein, a series of ZnCoS electrode materials with different morphologies were prepared by varying the solvent in the solvothermal reaction, and the effects of different microstructures on the electrochemical properties of ZnCoS were investigated. The ratio of water and ethanol in the solvent was controlled to modulate the microstructure of the as-prepared ZnCoS materials. XRD and XPS revealed the physical and chemical structure of the ZnCoS materials. SEM and TEM observations showed that the microstructure of ZnCoS transformed from one-dimensional wires to two-dimensional sheets with increasing amounts of ethanol. The maximum specific capacitance of the as-prepared ZnCoS materials is 6.22 F cm-2 at a current density of 5 mA cm-2, which is superior to that of most previously reported bimetallic sulfides. The enhanced electrochemical performance could be ascribed to its sheet-assembled spherical structure, which not only shortens the path of ion diffusion but also increases the contact between surface active sites and the electrolyte. Moreover, the spherical structure provides numerous void spaces for buffering the volume expansion and penetration of the electrolyte, which would be favorable for electrochemical reactions. Furthermore, the ZnCoS electrodes were coupled with activated carbon (AC) electrodes to build asymmetric supercapacitors (ASCs). The ASC device exhibits a maximum energy density of 0.124 mWh cm-2 under a power density of 2.1 mW cm-2. Moreover, even under a high-power density of 21 mW cm-2, the energy density can still reach 0.055 mWh cm-2.

Zeolitic Imidazolate Framework-Derived Zn/Co-S@Ni(OH)2 Nanoarrays with Excellent Energy Storage and Electrocatalytic Performance

The design and development of high-performance electrochemical electrode materials are crucial for energy storage and conversion systems. This work reports a facile preparation of a self-supported Zn/Co-S@Ni(OH)2 array electrode in which a Zn/Co-S nanosheet is derived from a leaf-like zeolitic imidazolate framework (Zn/Co-ZIF-L). The core-shell structure provides multiple benefits such as enhanced electrical conductivity, an abundance of exposed active sites, and strong electronic interactions between Zn/Co-S and ultra-thin Ni(OH)2 nanosheets, facilitating faster charge transfer. Consequently, Zn/Co-S@Ni(OH)2 demonstrates remarkable electrochemical characteristics as an electrode material for supercapacitors with an area capacitance of 12.9 F cm-2 at a current density of 2 mA cm-2 in 2 M KOH. The assembled asymmetric supercapacitor device achieves a high energy density of 0.95 mW h cm-2, while showing excellent longevity with a retention of 90.9% over 5000 cycles. Additionally, the Zn/Co-S@Ni(OH)2 arrays demonstrate significant oxygen evolution reaction activity with an overpotential of 242 mV at 10 mA cm-2 in 1 M KOH and significant stability for more than 100 h. This work provides a valuable approach for synthesizing bifunctional electrode materials for both energy storage and electrocatalysis applications.

3D Hierarchically Structured Tin Oxide and Iron Oxide-Embedded Carbon Nanofiber with Outermost Polypyrrole Layer for High-Performance Asymmetric Supercapacitor

Herein, unique three-dimensional (3D) hierarchically structured carbon nanofiber (CNF)/metal oxide/conducting polymer composite materials were successfully synthesized by combinations of various experimental methods. Firstly, base CNFs were synthesized by carbonization of electrospun PAN/PVP fibers to attain electric double-layer capacitor (EDLC) characteristics. To further enhance the capacitance, tin oxide (SnO2) and iron oxide (Fe2O3) were coated onto the CNFs via facile hydrothermal treatment. Finally, polypyrrole (PPy) was introduced as the outermost layer by a dispersion polymerization method under static condition to obtain 3D-structured CNF/SnO2/PPy and CNF/Fe2O3/PPy materials. With each synthesis step, the morphology and dimension of materials were transformed, which also added the benign characteristic for supercapacitor application. For the practical application, as-synthesized CNF/SnO2/PPy and CNF/Fe2O3/PPy were applied as active materials for supercapacitor electrodes, and superb specific capacitances of 508.1 and 426.8 F g-1 (at 1 A g-1) were obtained (three-electrode system). Furthermore, an asymmetric supercapacitor (ASC) device was assembled using CNF/SnO2/PPy as the positive electrode and CNF/Fe2O3/PPy as the negative electrode. The resulting CNF/SnO2/PPy//CNF/Fe2O3/PPy device exhibited excellent specific capacitance of 101.2 F g-1 (at 1 A g-1). Notably, the ASC device displayed a long-term cyclability (at 2000 cycles) with a retention rate of 81.1%, compared to a CNF/SnO2//CNF/Fe2O3 device of 70.3% without an outermost PPy layer. By introducing the outermost PPy layer, metal oxide detachment from CNFs were prevented to facilitate long-term cyclability of electrodes. Accordingly, this study provides an effective method for manufacturing a high-performance and stable supercapacitor by utilizing unique 3D hierarchical materials, comprised of CNF, metal oxide, and conducting polymer.

Multilevel spatial confinement of transition metal selenides porous microcubes for efficient and stable potassium storage

Recently, potassium-ion batteries (PIBs) have been considered as one of the most promising energy storage systems; however, the slow kinetics and large volume variation induced by the large radius of potassium ions (K⁺) during chemical reactions lead to inferior structural stability and weak electrochemical activity for most potassium storage anodes. Herein, a multilevel space confinement strategy is proposed for developing zinc-cobalt bimetallic selenide (ZnSe/Co_0.85Se@NC@C@rGO) as high-efficient anodes for PIBs by in-situ carbonizing and subsequently selenizing the resorcinol-formaldehyde (RF)-coated zeolitic imidazolate framework-8/zeolitic imidazolate framework-67 (ZIF-8/ZIF-67) encapsulated into 2D graphene. The highly porous carbon microcubes derived from ZIF-8/ZIF-67 and carbon shell arising from RF provide rich channels for ion/electron transfer, present a rigid skeleton to ensure the structural stability, offer space for accommodating the volume change, and minimize the agglomeration of active material during the insertion/extraction of large-radius K⁺. In addition, the three-dimensional (3D) carbon network composed of graphene and RF-derived carbon-coated microcubes accelerates the electron/ion transfer rate and improves the electrochemical reaction kinetics of the material. As a result, the as-synthesized ZnSe/Co_0.85Se@NC@C@rGO as the anode of PIBs possesses the excellent rate capability of 203.9 mA h g^-1 at 5 A g^-1 and brilliant long-term cycling performance of 234 mA h g^-1 after 2,000 cycles at 2 A g^-1. Ex-situ X-ray diffraction (Ex-situ XRD) diffraction reveals that the intercalation/de-intercalation of K⁺ proceeds through the conversion-alloying reaction. The proposed strategy based on the spatial confinement engineering is highly effective to construct high-performance anodes for PIBs.

Optimized Fabrication of Bimetallic ZnCo Metal-Organic Framework at NiCo-Layered Double Hydroxides for Multiple Storage and Capability Synergy All-Solid-State Supercapacitors

Rational design and structural regulation of hybrid nanomaterials with superior electrochemical performance are crucial for developing sustainable energy storage platforms. Among these materials, NiCo-layered double hydroxides (NiCo-LDHs) demonstrate an exceptional charge storage capabilities owing to their tunable 2D lamellar structure, large interlayer spacing, and rich redox electrochemically active sites. However, NiCo-LDHs still suffer from sever agglomeration of their particles with limited charge transfer rates, resulting in an inadequate rate capability. In this study, bimetallic ZnCo-metal organic framework (MOF) tripods were grown on the surface of NiCo-LDH nanowires, which significantly reduced the self-agglomeration and stacking of the NiCo-LDH nanowire arrays, offering more accessible active sites for charge transfer and shortening the path for ion diffusion. The fabricated hybrid ZnCo-MOF@NiCo-LDH and its individual counterparts were tested as supercapacitor electrodes. The ZnCo-MOF@NiCo-LDH electrode demonstrated a remarkable specific capacitance of 1611 F g^-1 at 2 A g^-1 with an enhanced rate capability of 66% from 2 to 20 A g^-1. Moreover, an asymmetric all solid-state supercapacitor device was constructed using ZnCo-MOF@NiCo-LDH and palm tree-derived activated carbon (P-AC) as positive and negative poles, respectively. The constructed device can store a high specific energy of 44.5 Wh Kg^-1 and deliver a specific power of 876.7 W Kg^-1 with outstanding Columbic efficiency over 10,000 charging/discharging cycles at 15 A g^-1.

g-C3N4-wrapped nickel doped zinc oxide/carbon core-double shell microspheres for high-performance photocatalytic hydrogen production

The development of efficient heterojunctions with enhanced photocatalytic properties is considered a promising approach for photocatalytic hydrogen production. In this study, graphitic carbon nitride (g-C₃N₄)-wrapped nickel-doped zinc oxide/carbon (Ni-ZnO@C/g-C₃N₄) core-double shell heterojunctions with unique core-double shell structures were employed as efficient photocatalysts through an innovative approach. Ni doping can enhance the intensity and range of visible light absorption in ZnO, and the carbon core coupled with the hollow double-shell structure can accelerate the charge transfer rate and improve the photon utilization efficiency. Meanwhile, the construction of the Z-scheme heterojunction extended the electron-hole pair transport path. In addition, the Z-scheme charge-transfer mechanism of Ni-ZnO@C/g-C₃N₄ under simulated sunlight was verified by photoluminescence (PL) and electron spin resonance (ESR) experiments. As a result, the obtained photocatalyst acquired a high hydrogen evolution rate of 336.08 μmol g^-1h^-1, which is 36.49 times higher than that of pristine ZnO. Overall, this work may provide a pathway for the construction of highly efficient photocatalysts with unique core-double shell structures.

Interface engineered hydrangea-like ZnCo2O4/NiCoGa-layered double hydroxide@polypyrrole core-shell heterostructure for high-performance hybrid supercapacitor

Rationally constructing advanced battery-type electrodes with hierarchical core-shell heterostructure is essential for improving the energy density and cycling stability of hybrid supercapacitors. Herein, this work successfully constructs hydrangea-like ZnCo₂O₄/NiCoGa-layered double hydroxide@polypyrrole (denoted as ZCO/NCG-LDH@PPy) core-shell heterostructure. Specifically, the ZCO/NCG-LDH@PPy employs ZCO nanoneedles clusters with large open void space and rough surfaces as the core, and NCG-LDH@PPy composite as the shell, comprising hexagonal NCG-LDH nanosheets with rich active surface area, and conductive PPy films with different thicknesses. Meanwhile, density functional theory (DFT) calculations authenticate the charge redistribution at the heterointerfaces between ZCO and NCG-LDH phases. Benefiting from the abundant heterointerfaces and synergistic effect among different active components, the ZCO/NCG-LDH@PPy electrode acquires an extraordinary specific capacity of 381.4 mAh g^-1 at 1 A g^-1, along with excellent cycling stability (89.83% capacity retention) after 10,000 cycles at 20 A g^-1. Furthermore, the prepared ZCO/NCG-LDH@PPy//AC hybrid supercapacitor (HSC) exhibits a remarkable energy density (81.9 Wh kg^-1), an outstanding power density (17,003.7 W kg^-1), and superior cycling performance (a capacitance retention of 88.41% and a coulombic efficiency of 93.97%) at the end of the 10,000th cycle. Finally, two ZCO/NCG-LDH@PPy//AC HSCs in series can light up a LED lamp for 15 min, indicating its excellent application prospects.

Photo-supercapacitors based on nanoscaled ZnO

In this study, zinc oxide (ZnO) powders in two different morphologies, nanowire (NW) and nanoflower (NF), have been synthesized by the hydrothermal method. The eligibility of the pristine ZnO nanopowders as a photo-active material has been revealed by designing P-SC devices via the facile drop-casting method on both glass and plastic substrates in large-area applications. The impact of physical properties and especially defect structures on photo-supercapacitor (P-SC) performance have been explored. Although the dark Coulombic efficiency (CE%) of both NW and NF-based P-SC were very close to each other, the CE% of NW P-SC increased 3 times, while the CE% of NF P-SC increased 1.7 times under the UV-light. This is because the charge carriers produced under light excitation, extend the discharge time, and as confirmed by electron paramagnetic resonance, photoluminescence, and transmission electron microscopy analyses, the performance of P-SCs made from NF powders was relatively low compared to those produced from NW due to the high core defects in NF powders. The energy density of 78.1 mWh kg⁻¹ obtained for NF-based P-SCs is very promising, and the capacitance retention value of almost 100% for 3000 cycles showed that the P-SCs produced from these materials were entirely stable. Compared to the literature, the P-SCs we propose in this study are essential for new generation energy storage systems, thanks to their ease of design, adaptability to mass production for large-area applications, and their ability to store more energy under illumination.

3D hierarchical ZnCo2S4@Ni(OH)2 nanowire arrays with excellent flexible energy storage and electrocatalytic performance

It is essential for energy storage and conversion systems to construct electrodes and electrocatalysts with superior performance. In this work, ZnCo₂S₄@Ni(OH)₂ nanowire arrays are synthesized on nickel foam by hydrothermal methods. As a supercapacitor electrode, the ZnCo₂S₄@Ni(OH)₂ structure exhibits a specific capacitance of 1,263.0C g^-1 at 1 A g^-1. The as-fabricated ZnCo₂S₄@Ni(OH)₂//active carbon device can achieve a maximum energy density of 115.4 Wh kg^-1 at a power density of 5,400 W kg^-1. As electrocatalysts, the ZnCo₂S₄@Ni(OH)₂ structure delivers outstanding performance for oxygen evolution reaction (an overpotential of 256.3 mV at 50 mA cm^-2), hydrogen evolution reaction (141.7 mV at 10 mA cm^-2), overall water splitting (the cell voltage of 1.53 V at 50 mA cm^-2), and a high stability for 13 h.

CoFe2O4 Hollow Spheres-Decorated Three-Dimensional rGO Sponge for Highly Efficient Electrochemical Charge Storage Devices

The energy demand, the crisis of fossil fuels, and the increasing popularity of portable and wearable electronics in the global market have triggered the demand to develop high-performance flexible all-solid-state supercapacitors that are capable of delivering high energy at high power density as well as being safely entrenched in those electronics. Herein, we have designed a nanocomposite, 80CFhs-20rGOsp, which exhibits a high specific capacitance (C S) value of 1032 F g-1 at 3 A g-1. Utilizing this nanocomposite as the cathode and reduced graphene oxide sponge (rGOsp) as the anode, a flexible all-solid-state asymmetric device has been fabricated. In this device, poly(vinyl alcohol) (PVA) gel embedded with a mixture of 3 M KOH and 0.1 M K4[Fe(CN)6] was used as an electrolyte cum separator. The fabricated device showed the capability to deliver an energy density of 65.8 W h kg-1 at a power density of 1500 W kg-1 and retained its capability even after various physical deformations. The device also exhibited a long cycle life and retained ∼96% of its C S value after 5000 cycles. Moreover, the fabricated flexible all-solid-state device successfully illuminated light-emitting diodes, which proved its potential use in real-life supercapacitor applications. The obtained results revealed the excellent electrochemical performances of the fabricated device and rendered it a promising candidate in the energy sector.

Magneto-Electrodeposition of 3D Cross-Linked NiCo-LDH for Flexible High-Performance Supercapacitors

Layered double hydroxides (LDHs) with outstanding redox activity on flexible current collectors can serve as ideal cathode materials for flexible hybrid supercapacitors in wearable energy storage devices. Electrodeposition is a facile, time-saving, and economical technique to fabricate LDHs. The limited loading mass induced by insufficient mass transport and finite exposure of active sites, however, greatly hinders the improvement of areal capacity. Herein, magneto-electrodeposition (MED) under high magnetic fields up to 9 T is developed to fabricate NiCo-LDH on flexible carbon cloth (CC) as well as Ti₃ C₂ T_x functionalized CC. Owing to the magneto-hydrodynamic effect induced by magnetic-electric field coupling, the loading mass and exposure of active sites are significantly increased. Moreover, a 3D cross-linked nest-like microstructure is constructed. The MED-derived NiCo-LDH delivers an ultrahigh areal capacity of 3.12 C cm^-2 at 1 mA cm^-2 and as-fabricated flexible hybrid supercapacitors show an excellent energy density with an outstanding cycling stability. This work provides a novel route to improve electrochemical performances of layered materials through MED technique.

Fabrication of three-dimensional WO3 nanotube bundles on carbon cloth as a binder-free electrode for high-performance supercapacitors

The WO3 nanotube bundles are fabricated on carbon cloth, exhibiting high specific capacitance, low charge transfer resistance, and excellent stability.

High performance flexible asymmetric supercapacitor constructed by cobalt aluminum layered double hydroxide @ nickel cobalt layered double hydroxide heterostructure grown in-situ on carbon cloth

HYPOTHESIS

Three-dimensional layered layered double hydroxide (LDH) nanostructure materials grow in-situ on excellent conductive and flexible carbon cloth (CC) substrate not only reduce the ability of binders in resisting ions transfer, but also make them to be quasi-vertically arranged well on substrates without aggregation. This would result in enough electroactive sites, to obtain superior electrochemical performance.

EXPERIMENTS

A hierarchical CoAl-LDH@NiCo-LDH composite was prepared on a surface-modified carbon cloth by a simple two-step hydrothermal process. In this process, CoAl-LDH nanosheets (NSs)/CC acting as the inner core were wrapped up in NiCo-LDH nanoneedle arrays (NNAs) evenly. Also, a flexible quasi-solid-state supercapacitor device was constructed using CoAl-LDH@NiCo-LDH/CC and activated carbon (AC) as a positive electrode and a negative electrode, respectively.

FINDINGS

The CoAl-LDH@NiCo-LDH/CC developed had an excellent specific capacitance (2633.6F/g at 1 A/g) with remarkable cyclic performance (92.5% retention of its incipient over 5000 cycles at 4 A/g). The flexible quasi-solid-state supercapacitor device CoAl-LDH@NiCo-LDH/CC//AC/CC yielded a splendid energy density of 57.8 Wh/kg at a power density of 0.81 kW/kg and a brilliant power density of 16.09 kW/kg at 38.0 Wh/kg in a broad potential window of 1.55 V. Furthermore, the exceptional cyclic stability and excellent flexibility of the device show it can be applied in flexible energy storage systems.

Flexible free-standing Ni-Mn oxide antenna decorated CNT/nanofiber membrane for high-volumetric capacitance supercapacitors

There is growing demand for lightweight flexible supercapacitors with high electrochemical performance for wearable and portable electronics. Here, we spun nanoparticles of nickel-manganese oxides along with carbon nanotubes into carbon nanofibers and engineered a 3D networked Ni-Mn oxides/CNT@CNF free-standing membrane for flexible supercapacitor applications. The electrospinning process controlled the nanoparticle aggregation while subsequent heat treatment generates nanochannels in the fibres, resulting in a very porous tubular nanocomposite structure. The preparation process also enabled good interfacial contact between the nanoparticles and the conductive carbon network. The resulting Ni-Mn oxides/CNT@CNF membrane displays high mass loading (Ni-Mn oxides) of 855 mg cm^-3 and low CNT incorporation of ∼0.4%. The outstanding porous structure, synergy of the carbon with Ni-Mn oxides, and fast and facile faradaic reactions on the electrode were responsible for the superior volumetric capacitance of 250 F cm^-3 at 1 A cm^-3, energy density as high as 22 mW h cm^-3 and an excellent power density of 12 W cm^-3. Despite the low CNT loading, the hybrid electrode exhibits excellent cycling performance with capacitance retention of 96.4% after 10 000 cycles evidencing a well-preserved Ni-manganese oxide nanostructure throughout the cycling. The resulting outstanding electrochemical performances of the Ni-Mn oxides/CNT@CNF synergic system offer new insights into effective utilization of transition metal oxides for establishing high-performance flexible supercapacitors within a confined volume.

A Review of Supercapacitors: Materials Design, Modification, and Applications

Supercapacitors (SCs) have received much interest due to their enhanced electrochemical performance, superior cycling life, excellent specific power, and fast charging–discharging rate. The energy density of SCs is comparable to batteries; however, their power density and cyclability are higher by several orders of magnitude relative to batteries, making them a flexible and compromising energy storage alternative, provided a proper design and efficient materials are used. This review emphasizes various types of SCs, such as electrochemical double-layer capacitors, hybrid supercapacitors, and pseudo-supercapacitors. Furthermore, various synthesis strategies, including sol-gel, electro-polymerization, hydrothermal, co-precipitation, chemical vapor deposition, direct coating, vacuum filtration, de-alloying, microwave auxiliary, in situ polymerization, electro-spinning, silar, carbonization, dipping, and drying methods, are discussed. Furthermore, various functionalizations of SC electrode materials are summarized. In addition to their potential applications, brief insights into the recent advances and associated problems are provided, along with conclusions. This review is a noteworthy addition because of its simplicity and conciseness with regard to SCs, which can be helpful for researchers who are not directly involved in electrochemical energy storage.

Magnetic-Nanowaxberry-Based Simultaneous Detection of Exosome and Exosomal Proteins for the Intelligent Diagnosis of Cancer

Exosome concentration and exosomal proteins are regarded as promising cancer biomarkers. Herein, a waxberry-like magnetic bead (magnetic-nanowaxberry) which has huge surface area and strong affinity was synthesized to couple with aptamer for exosome capture and recovery. Subsequently, we developed a fluorescent assay for the sensitive, accurate, and simultaneous quantification of exosome and cancer-related exosomal proteins [epidermal growth factor receptor (EGFR) and epithelial cell adhesion molecule (EpCAM)] by using triple-colored probes to recognize EGFR and EpCAM or spontaneously anchor to the lipid bilayer. In this design, the interference of soluble proteins can be avoided due to the dual recognition strategy. Moreover, the lipid-based quantification of exosome concentration can improve the accuracy. Besides, the simultaneous detection mode can save samples and simplify the operation steps. Consequently, the assay shows high sensitivity (the limits of detection are down to 0.96 pg/mL for EGFR, 0.19 pg/mL for EpCAM, and 2.4 × 10⁴ particles/μL for exosome), high specificity, and satisfactory accuracy. More importantly, this technique is successfully used to analyze exosomes in plasma to distinguish cancer patients from healthy individuals. To improve the diagnostic efficacy, the deep learning was used to exploit the potential pattern hidden in data obtained by the proposed method. Also, the accuracy for the intelligent diagnosis of cancer can achieve 96.0%. This study provides a new avenue for developing new biosensors for exosome analysis and intelligent disease diagnosis.

Synthesis of novel Co3O4 nanocubes-NiO octahedral hybrids for electrochemical energy storage supercapacitors

Fabrication of novel metal oxide nanostructured composites is a proficient approach to develop efficient energy storage devices and development of cost-free and eco-friendly metal oxide nanostructures for supercapacitor applications received considerable attention in recent years. The Co₃O₄ nanocubes-NiO octahedral structured composite was constructed using facile and one-step calcination process. Cyclic voltammetry, charge-discharge, and electrochemical impedance spectral techniques have been employed to analyze the specific capacitance of the synthesized nanostructures and the composites. Specific capacitance and cycling stability of the composites were evaluated with the pristine Co₃O₄ and NiO nanostructures. The composite showed a specific capacitance of 832 F g^-1 at a current density of 0.25 A g^-1, which was ~1.5 and ~1.9-times higher than pristine Co₃O₄ nanocubes and NiO octahedral structure, respectively. On the other hand, electrode showed approximately 50 % capacity retention at a higher current density (5 Ag^-1) because of the uniform morphology of Co₃O₄ and NiO. The charge-discharge stability measurements of the composite showed an admirable specific capacitance retention capability, which was 94.5 % after 2000 continuous charge-discharge cycles at a current density of 5 A g^-1. The superior electrochemical performance of the nano-composite was ascribed to synergistic effects and uniform morphology. Efficient nanostructure development using facile and one-step calcination process and electrochemical performance make the synthesized composite a promising device for supercapacitor applications.

Origami and layered-shaped ZnNiFe-LDH synthesized on Cu(OH)2 nanorods array to enhance the energy storage capability

The combination of layered nanorod arrays with unique core-shell structure and transition metal layered double hydroxide (LDH) is considered as a feasible solution to improve the electrochemical performances of capacitor electrode. In this study, layered ZnNiFe-LDH@Cu(OH)₂/CF core-shell nanorod arrays, which consist of ultrathin ZnNiFe-LDHs nanosheet shells and ordered Cu(OH)₂ nanorod inner cores, are successfully designed and fabricated by a typical hydrothermal way and a simple in situ oxidation reaction. The electrode prepared using ZnNiFe-LDH@Cu(OH)₂/CF nanomaterial reveals an remarkable area capacitance of 6100 mF cm^-2 at 3 mA cm^-2 current density, which is excellently superior than those of ZnFe-LDH@Cu(OH)₂/CF, NiFe-LDH@Cu(OH)₂/CF, Cu(OH)₂/CF and CF. Additionally, the capacitance retention remains as high as 83.4% after 5000 cycles and a very small Rs (0.567 Ω) can be observed. In addition, an asymmetric supercapacitor device is successfully fabricated employing ZnNiFe-LDH@Cu(OH)₂/CF. Meanwhile, the ZnNiFe-LDH@Cu(OH)₂/CF//AC device can achieve an energy density of 44 Wh kg^-1 and a corresponding power density of 720 W kg^-1 and possess the capability to light up a multi-function monitor for 33 min just using two ASC equipments connected in series. Therefore, the prepared ZnNiFe-LDH@Cu(OH)₂/CF composite materials with unique structure has great application potential in energy storage devices.

Carbon coating on metal oxide materials for electrochemical energy storage

During the past decades, nano-structured metal oxide electrode materials have received growing attention due to their low development cost and high theoretical specific capacity, accordingly, quite a lot of metal oxide electrode materials are being used in electrochemical energy storage devices. However, the further development was limited by the relatively low electrical conductivity and the volume expansion during electrochemical reactions. Thus, many approaches have been proposed to obtain high-efficiency metal oxide electrode materials, such as designing nanomaterials with ideal morphology and high specific surface area, optimizing with carbon-based materials (such as graphene and glucose) to prepare nanocomposites, combining with conductive substrates to enhance the conductivity of electrodes, etc. Owning to the advantages of low cost and high chemical stability of carbon materials, core-shell structure formed by carbon-coated metal oxides is considered to be a promising solution to solve these problems. Therefore, this review mainly focuses on recent research advances in the field of carbon-coated metal oxides for energy storage, summarizing the advantages and disadvantages of common metal oxides and different types of carbon sources, and proposing methods to optimize the material properties in terms of structure and morphology, carbon layer thickness, coating method, specific surface area and pore size distribution, as well as improving electrical conductivity. In addition, the double or multi-layer coating strategy is also a reflection of the continuous development of carbon coating method. Hopefully, this rereview may provide a new direction for the renewal and development of future energy storage electrode materials.

When Conductive MOFs Meet MnO2: High Electrochemical Energy Storage Performance in an Aqueous Asymmetric Supercapacitor

Metal organic frameworks (MOFs) have been widely researched and applied in many fields. However, the poor electrical conductivity of many traditional MOFs greatly limits their application in electrochemistry, especially in energy storage. Benefited from the full charge delocalization in the atomical plane, conductive MOFs (c-MOFs) exhibit good electrochemical performance. Besides, unlike graphene, c-MOFs are provided with 1D cylindrical channels, which can facilitate the ion transport and enable high ion conductivity. Transition-metal oxides (TMOs) are promising materials with good electrochemical energy storage performance due to their excellent oxidation-reduction activity. When composited with TMOs, the c-MOFs can significantly improve the capacitance and rate performance. In this work, for the first time, we designed serial MnO₂@Ni-HHTP (HHTP = 2,3,6,7,10,11-hexahydroxytriphenylene) nanoarrays with different lengths and explored how the lengths influence the electrochemical energy storage performance. By taking advantage of the high redox activity of MnO₂ and the excellent electron and ion conductivity in Ni-HHTP, when assembled as the positive electrode material in an aqueous asymmetric supercapacitor, the device displays high energy density, outstanding rate performance, and superior cycle stability. We believe that the results of this work would provide a good prospect for developing other c-MOF composites as a potential class of electrode materials in energy storage and conversion.

Novel Dealloying-Fabricated NiS/NiO Nanoparticles with Superior Cycling Stability for Supercapacitors

NiS/NiO nanoparticles are successfully fabricated through a simple dealloying method and an ion-exchange process. X-ray diffraction demonstrates the existence of NiO and NiS phases, and scanning electron microscopy and transmission electron microscopy imply the nanopore distribution nature and the nanoparticle morphology of the produced material. The electrochemical behaviors are studied by cyclic voltammetry and galvanostatic charge-discharge measurements. The NiS/NiO electrode shows an enhanced specific capacitance of 1260 F g-1 at a current density of 0.5 A g-1. The NiS/NiO//AC device provides a maximum energy density of 17.42 W h kg-1, a high power density of 4000 W kg-1, and a satisfactory cycling performance of 93% capacitance retention after 30,000 cycles.

Metal-Organic Framework-Derived ZnSe- and Co0.85Se-Filled Porous Nitrogen-Doped Carbon Nanocubes Interconnected by Reduced Graphene Oxide for Sodium-Ion Battery Anodes

Transition-metal selenides have been considered as one of the most promising anode materials for sodium-ion batteries (SIBs) due to their high theoretical capacity and excellent rate performance. However, rapid capacity decay and poor cycling stability limit their practical application as the anode for SIBs. Carbon coating is one of the most effective ways to solve the above problems, but the thickness and uniformity of the coating layer are difficult to control. Herein, we successfully synthesize metal-organic framework (MOF)-derived porous N-doped carbon nanocubes homogeneously filled with ZnSe and Co_0.85Se and interconnected by reduced graphene oxide (ZCS@NC@rGO). ZCS@NC@rGO with more active sites and the synergistic effect of the ZnSe and Co_0.85Se heterojunction can enhance the sodium storage performance. The porous carbon nanocubes effectively prevent the agglomeration of active particles, and the rGO acting as a carbon network can significantly buffer the inevitable volume changes. At the same time, carbon nanocubes and the rGO are interconnecting to form a conductive network to accelerate electron transfer. Based on the aforementioned advantages, the ZCS@NC@rGO electrode shows an excellent sodium storage performance. Our investigation opens up a new horizon for the rational design of transition-metal selenide anodes for SIBs with a unique structure.

Transition metal dichalcogenide (TMDs) electrodes for supercapacitors: a comprehensive review

As globally, the main focus of the researchers is to develop novel electrode materials that exhibit high energy and power density for efficient performance energy storage devices. This review covers the up-to-date progress achieved in transition metal dichalcogenides (TMDs) (e.g. MoS₂, WS₂, MoSe_2,and WSe₂) as electrode material for supercapacitors (SCs). The TMDs have remarkable properties like large surface area, high electrical conductivity with variable oxidation states. These properties enable the TMDs as the most promising candidates to store electrical energy via hybrid charge storage mechanisms. Consequently, this review article provides a detailed study of TMDs structure, properties, and evolution. The characteristics technique and electrochemical performances of all the efficient TMDs are highlighted meticulously. In brief, the present review article shines a light on the structural and electrochemical properties of TMD electrodes. Furthermore, the latest fabricated TMDs based symmetric/asymmetric SCs have also been reported.

Transition Metal Oxide Electrode Materials for Supercapacitors: A Review of Recent Developments

In the past decades, the energy consumption of nonrenewable fossil fuels has been increasing, which severely threatens human life. Thus, it is very urgent to develop renewable and reliable energy storage devices with features of environmental harmlessness and low cost. High power density, excellent cycle stability, and a fast charge/discharge process make supercapacitors a promising energy device. However, the energy density of supercapacitors is still less than that of ordinary batteries. As is known to all, the electrochemical performance of supercapacitors is largely dependent on electrode materials. In this review, we firstly introduced six typical transition metal oxides (TMOs) for supercapacitor electrodes, including RuO₂, Co₃O₄, MnO₂, ZnO, XCo₂O₄ (X = Mn, Cu, Ni), and AMoO₄ (A = Co, Mn, Ni, Zn). Secondly, the problems of these TMOs in practical application are presented and the corresponding feasible solutions are clarified. Then, we summarize the latest developments of the six TMOs for supercapacitor electrodes. Finally, we discuss the developing trend of supercapacitors and give some recommendations for the future of supercapacitors.

Enhancing electrochemical performance of electrode material via combining defect and heterojunction engineering for supercapacitors

The poor conductivity and deficient active sites of transition metal oxides lead to low energy density of supercapacitors, which limits their wide application. In this work, double transition metal oxide heterojunctions with oxygen vacancy (V_o-ZnO/CoO) nanowires are prepared by effective hydrothermal and thermal treatments. The formation of the heterojunction results in the redistribution of interface charge between ZnO and CoO, generating an internal electric field to accelerate the electron transport. Meanwhile, oxygen vacancies can enhance the redox reaction activity to further improve the electrochemical kinetics of the electrode material. Therefore, the prepared V_o-ZnO/CoO can provide a superior specific capacity of 845 C g^-1 (1 A g^-1). An asymmetric supercapacitor with the V_o-ZnO/CoO as positive electrode shows a higher energy density of 51.6 Wh kg^-1 when the power density reaches 799.9 W kg^-1. This work proposes a synergistic combination of defect and heterojunction engineering to improve the electrochemical properties of materials, providing an important guidance for material design in energy-storage field.