Carbon nanomaterials supported Ni(OH)2/NiO hybrid flower structure for supercapacitor

Concrete-based energy storage: exploring electrode and electrolyte enhancements

The exploration of concrete-based energy storage devices represents a demanding field of research that aligns with the emerging concept of creating multifunctional and intelligent building solutions. The increasing need to attain zero carbon emissions and harness renewable energy sources underscores the importance of advancing energy storage technologies. A recent focus has been on structural supercapacitors, which not only store electrochemical energy but also support mechanical loads, presenting a promising avenue for research. We comprehensively review concrete-based energy storage devices, focusing on their unique properties, such as durability, widespread availability, low environmental impact, and advantages. First, we elucidate how concrete and its composites revolutionize basic building blocks for the design and fabrication of intrinsically strong structural materials. Afterward, we categorized concrete into two major parts of a supercapacitor, i.e., electrode and electrolyte materials. We further describe the synthesis of concrete-based electrodes and electrolytes and highlight the main points to be addressed while synthesizing porous surface/electroactive matrices. The incorporation of carbon, polymers, metals, etc., enhances the energy density and durability of electrode materials. Furthermore, as an electrolyte, how concrete accommodates metal salts and the mode of diffusion/transport have been described. Although pure concrete electrolytes exhibit poor ionic conductivity, the addition of conducting polymers, metal/metal oxides, and carbon increases the overall performance of energy storage devices. At the end of the review, we discuss the challenges and perspectives on future research directions and provide overall conclusions.

Controlling the Cooling Rate of Hydrothermal Synthesis to Enhance the Supercapacitive Properties of β-Nickel Hydroxide Electrode Materials

The demand for power storage devices with good quality, fast charging and high energy density is becoming more and more urgent in today's electronic technology. For batteries and traditional capacitors, it is an insurmountable challenge to combine fast charging and discharging, large capacitance and long-life properties. The characteristics of supercapacitors can meet all the above requirements at the same time. In this study, a simple one-step hydrothermal method was successfully used to grow β-nickel hydroxide nanocone particles directly on the 3D foamed nickel substrate as a working electrode material for supercapacitors. After growing β-nickel hydroxide crystals on 3D foamed nickel substrate, by controlling the cooling rate, a well-crystalized β-nickel hydroxide with good capacitance characteristics can be obtained. Cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) were used to analyze the capacitance characteristics of the β-nickel hydroxide electrode. The research results show that the specific capacitance value of the β-Ni(OH)2/3D nickel foam electrode material prepared at the cooling rate of 10 °C/h can reach 539 F/g with the charge-discharge test at a current density of 3 A/g. After 1000 continuous charge and discharge cycles, the material still retains 94.1% of the specific capacitance value.

An Overview of the Emerging Technologies and Composite Materials for Supercapacitors in Energy Storage Applications

Energy storage is one of the challenges currently confronting the energy sector. However, the invention of supercapacitors has transformed the sector. This modern technology's high energy capacity, reliable supply with minimal lag time, and extended lifetime of supercapacitors have piqued the interest of scientists, and several investigations have been conducted to improve their development. However, there is room for improvement. Consequently, this review presents an up-to-date investigation of different supercapacitor technologies' components, operating techniques, potential applications, technical difficulties, benefits, and drawbacks. In addition, it thoroughly highlights the active materials used to produce supercapacitors. The significance of incorporating every component (electrode and electrolyte), their synthesis approach, and their electrochemical characteristics are outlined. The research further examines supercapacitors' potential in the next era of energy technology. Finally, concerns and new research prospects in hybrid supercapacitor-based energy applications that are envisaged to result in the development of ground-breaking devices, are highlighted.

Battery-Type-Behavior-Retention Ni(OH)2-rGO Composite for an Ultrahigh-Specific-Capacity Asymmetric Electrochemical Capacitor Electrode

Nanosized battery-type materials applied in electrochemical capacitors can effectively reduce a series of problems caused by low conductivity and large volume changes. However, this approach will lead to the charging and discharging process being dominated by capacitive behavior, resulting in a serious decline in the specific capacity of the material. By controlling the material particles to an appropriate size and a suitable number of nanosheet layers, the battery-type behavior can be retained to maintain a large capacity. Here, Ni(OH)₂, which is a typical battery-type material, is grown on the surface of reduced graphene oxide to prepare a composite electrode. By controlling the dosage of the nickel source, the composite material with an appropriate Ni(OH)₂ nanosheet size and a suitable number of layers was prepared. The high-capacity electrode material was obtained by retaining the battery-type behavior. The prepared electrode had a specific capacity of 397.22 mA h g^-1 at 2 A g^-1. After the current density was increased to 20 A g^-1, the retention rate was as high as 84%. The prepared asymmetric electrochemical capacitor had an energy density of 30.91 W h kg^-1 at a power density of 1319.86 W kg^-1 and the retention rate could reach 79% after 20,000 cycles. We advocate an optimization strategy that retains the battery-type behavior of electrode materials by increasing the size of nanosheets and the number of layers, which can significantly improve the energy density while combining the advantage of the high rate capability of the electrochemical capacitor.

Repairing of Subchondral Defect and Articular Cartilage of Knee Joint of Rabbit by Gadolinium Containing Bio-Nanocomposites

A variety of gadolinium (Gd) based nanoparticles (NPs) were synthesized due to the unique magnetic properties of Gd-containing rare earth compounds and the particularity of micro/nano-materials, which were then incorporated into hydroxyapatite (HA) to obtain inorganic-organic composite materials. Then, HA/Gd NPs containing slow-release transforming growth factor (TGF-β1) were harvested. Adipose-derived stem cells (ADSCs) were extracted from the adipose tissue of a four-month-old New Zealand white rabbit. HA/Gd NPs were attached to absorbable gelatin sponge to obtain HA/Gd NPs/gelatin sponge composite scaffold. In addition, the third generation ADSCs were taken and cultured in the composite scaffold, so that ADSCs-HA/Gd bio-nanocomposites were obtained. The in vitro culture test of osteoblast MC3T3-E1 showed that Gd-containing NPs had good biocompatibility. The prepared HA/Gd NPs loaded with TGF-β1 were spherical, with an average particle size of (9.16 ± 3.16) μm. The NPs were easy to aggregate and adherent. Enzyme-linked immunosorbent assay (ELISA) test results showed that TGF-β1 in NPs was sustained and released continuously for 29 days. HA/Gd NPs/gelatin sponge composite scaffold combined with ADSCs were co-cultured for three days, and the electron microscope showed that the HA/Gd NPs were dispersed, and the cells could adhere and grow well. Then, animal models of rabbit knee articular cartilage defects were established and were rolled into three groups (ADSCs-HA/Gd nano group, HA/Gd nano scaffold group, and blank control). The repair area of the rabbit knee of ADSCs-HA/Gd nano group was smooth and flat, the scaffold was absorbed, the toluidine blue stain was positive, and the type II collagen immunohistochemical stain was positive. In general, ADSCs-HA/Gd nanomaterials were helpful for chondrogenic cell differentiation and had certain adoption prospects in the field of tissue engineering to repair cartilage defects.

A light-fostered supercapacitor performance of multi-layered ReS2 grown on conducting substrates

The light-fostered supercapacitor performance introduces a new realm in the field of smart energy storage applications. Transition metal dichalcogenides (TMDCs) with direct band gap are intriguing candidates for developing a light-induced supercapacitor that can enhance energy storage when shined with light. Many TMDCs show a transition from a direct to indirect band gap as the layer number increases, while ReS2 possesses a direct band gap in both bulk and monolayer forms. The growth of such multi-layered 2D materials with high surface area on conducting substrates makes them suitable for smart energy storage applications with the ability to tune their performance with light irradiation. In this report, we present the growth of vertically aligned multi-layered ReS2 with large areal coverage on various conducting and non-conducting substrates, including stainless steel via chemical vapor deposition (CVD). To investigate the effect of light illumination on the charge storage performance, electrochemical measurements have been performed in dark and light conditions. Cyclic voltammetry (CV) curves showed an increase in the area enclosed by the curve, manifesting the increased charge storage capacity under light illumination as compared to dark. The volumetric capacitance value calculated from charging-discharging curves has increased from 17.9 F cm-3 to 29.8 F cm-3 with the irradiation of light for the as-grown ReS2 on a stainless steel plate. More than 1.5 times the capacitance enhancement is attributed to excess electron-hole pairs generated upon light illumination, contributing to the charge storage in the presence of light. The electrochemical impedance spectroscopy further augments these results. The high cyclic stability is attained with a capacitance retention value of 81% even after 10 000 repeated charging-discharging cycles.

One-step carbonization of a nickel-containing nitrogen-doped porous carbon material for electrochemical supercapacitors

Improving the graphitization degree of materials by Ni metal catalysis, so as to enhance the electrical properties of the material.

Preparation and Performance of Porous Carbon Nanocomposite from Renewable Phenolic Resin and Halloysite Nanotube

The growing demand for high performance from supercapacitors has inspired the development of porous nanocomposites using renewable and naturally available materials. In this work, a formaldehyde-free phenolic resin using monosaccharide-based furfural was synthesized to act as the carbon precursor. One dimensional halloysite nanotube (HNT) with high porosity and excellent cation/anion exchange capacity was mixed with the phenol-furfural resin to fabricate carbonaceous nanocomposite HNT/C. Their structure and porosity were characterized. The effects of the halloysite nanotube amount and carbonization temperature on the electrochemical properties of HNT/C were explored. HNT/C exhibited rich porosity, involving a large specific surface area 253 m²·g⁻¹ with a total pore volume of 0.27 cm³·g⁻¹. The electrochemical performance of HNT/C was characterized in the three-electrode system and showed enhanced specific capacitance of 146 F·g⁻¹ at 0.2 A g⁻¹ (68 F·g⁻¹ for pristine carbon) in electrolyte (6 mol·L⁻¹ KOH) and a good rate capability of 62% at 3 A g⁻¹. It also displayed excellent cycle performance with capacitance retention of 98.5% after 500 cycles. The symmetric supercapacitors with HNT/C-1:1.5-800 electrodes were fabricated, exhibiting a high energy density of 20.28 Wh·Kg⁻¹ at a power density of 100 W·Kg⁻¹ in 1 M Na₂SO₄ electrolyte. The present work provides a feasible method for preparing composite electrode materials with a porous structure from renewable phenol-furfural resin and HNT. The excellent supercapacitance highlights the potential applications of HNT/C in energy storage.

Temperature controlled diffusion of hydroxide ions in 1D channels of Ni-MOF-74 for its complete conformal hydrolysis to hierarchical Ni(OH)2 supercapacitor electrodes

Conformal hydrolysis of MOF precursors is a promising strategy to prepare hierarchical metal hydroxide electrode materials on a large scale with low cost and high efficiency. However, a complete transformation is challenging due to the normal "outside-in" conversion process. After studying the hydrolysis of Ni-MOF-74, which has regular 1D channels, we suggest that the transformation to Ni(OH)2 can occur simultaneously outside and within the precursor depending on the treatment temperature. Molecular dynamics simulations reveal that a higher temperature weakens the steric effects of OH- ions and facilitates the diffusion in the regular channels, and therefore, a complete transformation from Ni-MOF-74 to Ni(OH)2 is achieved. It is for the first time demonstrated that the 1D channels of MOFs are utilized for the complete conformal hydrolysis of Ni-MOF-74 to Ni(OH)2 electrode materials. Meanwhile, we also perform pioneering work illustrating that the complete conformal hydrolysis is the key to the improved supercapacitor performances of the MOF-derived Ni(OH)2 electrodes. The prepared Ni(OH)2 electrode under the optimized conditions has a specific capacity of 713.2 C g-1 at a current density of 1 A g-1, which is at least 28% larger than those of the Ni(OH)2 prepared at other temperatures. The detailed analyses based on CV and EIS of the obtained Ni(OH)2 electrodes indicate that the residual MOFs within electrodes due to incomplete hydrolysis significantly influence the diffusion length and diffusion efficiency of OH-, drastically lowering the supercapacitor performances.

Facile synthesis of Al-doped NiO nanosheet arrays for high-performance supercapacitors

Electrode material design is the key to the development of asymmetric supercapacitors with high electrochemical performances and stability. In this work, Al-doped NiO nanosheet arrays were synthesized using a facile hydrothermal method followed by a calcination process, and the synthesized arrays exhibited a superior pseudocapacitive performance, including a favourable specific capacitance of 2253 ± 105 F g-1 at a current density of 1 A g-1, larger than that of an undoped NiO electrode (1538 ± 80 F g-1). More importantly, the arrays showed a high-rate capability (75% capacitance retention at 20 A g-1) and a high cycling stability (approx. 99% maintained after 5000 cycles). The above efficient capacitive performance benefits from the large electrochemically active area and enhanced conductivity of the arrays. Furthermore, an assembled asymmetric supercapacitor based on the Al-doped NiO arrays and N-doped multiwalled carbon nanotube ones delivered a high specific capacitance of 192 ± 23 F g-1 at 0.4 A g-1 with a high-energy density of 215 ± 15 Wh kg-1 and power density of 21.6 kW kg-1. Additionally, the asymmetric device exhibited a durable cyclic stability (approx. 100% retention after 5000 cycles). This work with the proposed doping method will be beneficial to the construction of high-performance supercapacitor systems.

Atomic Layer Deposition of Nickel on ZnO Nanowire Arrays for High-Performance Supercapacitors

A novel hybrid core-shell structure of ZnO nanowires (NWs)/Ni as a pseudocapacitor electrode was successfully fabricated by atomic layer deposition of a nickel shell, and its capacitive performance was systemically investigated. Transmission electron microscopy and X-ray photoelectron spectroscopy results indicated that the NiO was formed at the interface between ZnO and Ni where the Ni was oxidized by ZnO during the ALD of the Ni layer. Electrochemical measurement results revealed that the Ti/ZnO NWs/Ni (1500 cycles) electrode with a 30 nm thick Ni-NiO shell layer had the best supercapacitor properties including ultrahigh specific capacitance (∼2440 F g^-1), good rate capability (80.5%) under high current charge-discharge conditions, and a relatively better cycling stability (86.7% of the initial value remained after 750 cycles at 10 A g^-1). These attractive capacitive behaviors are mainly attributed to the unique core-shell structure and the combined effect of ZnO NW arrays as short charge transfer pathways for ion diffusion and electron transfer as well as conductive Ni serving as channel for the fast electron transport to Ti substrate. This high-performance Ti/ZnO NWs/Ni hybrid structure is expected to be one of a promising electrodes for high-performance supercapacitor applications.

Optimizing crystallinity and porosity of hierarchical Ni(OH)2 through conformal transformation of metal–organic framework template for supercapacitor applications

Conformal hydrolysis of MOFs (metal–organic frameworks) yields high-performance supercapacitor electrodes.

Controllable synthesis of hierarchical nickel hydroxide nanotubes for high performance supercapacitors

Hierarchical Ni(OH)₂ nanotubes synthesized by a self-sacrificial template method exhibit superior capacitance and stability as electrode materials for supercapacitors.

One material, multiple functions: graphene/Ni(OH)2 thin films applied in batteries, electrochromism and sensors

Different nanocomposites between reduced graphene oxide (rGO) and Ni(OH)₂ nanoparticles were synthesized through modifications in the polyol method (starting from graphene oxide (GO) dispersion in ethylene glycol and nickel acetate), processed as thin films through the liquid-liquid interfacial route, homogeneously deposited over transparent electrodes and spectroscopically, microscopically and electrochemically characterized. The thin and transparent nanocomposite films (112 to 513 nm thickness, 62.6 to 19.9% transmittance at 550 nm) consist of α-Ni(OH)₂ nanoparticles (mean diameter of 4.9 nm) homogeneously decorating the rGO sheets. As a control sample, neat Ni(OH)₂ was prepared in the same way, consisting of porous nanoparticles with diameter ranging from 30 to 80 nm. The nanocomposite thin films present multifunctionality and they were applied as electrodes to alkaline batteries, as electrochromic material and as active component to electrochemical sensor to glycerol. In all the cases the nanocomposite films presented better performances when compared to the neat Ni(OH)₂ nanoparticles, showing energy and power of 43.7 W h kg⁻¹ and 4.8 kW kg⁻¹ (8.24 A g⁻¹) respectively, electrochromic efficiency reaching 70 cm² C⁻¹ and limit of detection as low as 15.4 ± 1.2 μmol L⁻¹.

In situ synthesis of 3D CoS nanoflake/Ni(OH)₂ nanosheet nanocomposite structure as a candidate supercapacitor electrode

A three-dimensional (3D) CoS/Ni(OH)2 nanocomposite structure based on CoS nanoflakes and two-dimensional (2D) Ni(OH)2 nanosheets were in situ synthesized on Ni foam by a whole hydrothermal reaction and electrodeposition process. The 3D CoS/Ni(OH)2 nanocomposite structures demonstrate the combined advantages of a sustained cycle stability of CoS and high specific capacitance from Ni(OH)2. The obtained CoS/Ni(OH)2 nanocomposite structures on Ni foam can directly serve as a binder-free electrode for a supercapacitor. For the 3D CoS/Ni(OH)2 nanocomposite electrode, the high specific capacitance is 1837 F g(-1) at a scan rate of 1 mV s(-1), which is obviously higher than both the bare CoS electrode and Ni(OH)2 electrode. The galvanostatic charge and discharge measurements illustrate that the 3D CoS/Ni(OH)2 nanocomposite electrode possesses excellent cycle stability, and it keeps a 95.8% retention of the initial capacity after 5000 cycles. Electrochemical impedance spectroscopy measurements also confirm that the 3D CoS/Ni(OH)2 nanocomposite electrode has better electrochemical characteristics. These remarkable performances can be attributed to the unique 3D nanoporous structure of CoS/Ni(OH)2 which leads to a large accessible surface area and a high stability during long-term operation. In addition, 2D Ni(OH)2 nanosheets in 3D nanocomposite structures can afford rapid mass transport and a strong synergistic effect of CoS and Ni(OH)2 as individual compositions contribute to the high performance of the nanocomposite structure electrode. These results may promote the design and implementation of nanocomposite structures in advanced supercapacitors.

Self-Assembled NiO/Ni(OH)2 Nanoflakes as Active Material for High-Power and High-Energy Hybrid Rechargeable Battery

Herein, a proof-of-concept of novel hybrid rechargeable battery based on electrochemical reactions of both nickel-zinc and zinc-air batteries is demonstrated using NiO/Ni(OH)2 nanoflakes self-assembled into mesoporous spheres as the active electrode material. The hybrid battery operates on two sets of fundamentally different battery reactions combined at the cell level, unlike in other hybrid systems where batteries of different reactions are simply connected through an external circuitry. As a result of combining nickel-zinc and zinc-air reactions, the hybrid battery demonstrates both remarkably high power density (volumetric, 14 000 W L(-1); gravimetric, 2700 W kg(-1)) and energy density of 980 W h kg(-1), significantly outperforming the performances of a conventional zinc-air battery. Furthermore, the hybrid battery demonstrates excellent charge rate capability up to 10 times faster than the rate of discharge without any capacity and voltage degradations, which makes it highly suited for large-scale applications such as electric vehicle propulsion and smart-grid energy storage.

Mesoporous Transition Metal Oxides for Supercapacitors

Recently, transition metal oxides, such as ruthenium oxide (RuO₂), manganese dioxide (MnO₂), nickel oxides (NiO) and cobalt oxide (Co₃O₄), have been widely investigated as electrode materials for pseudo-capacitors. In particular, these metal oxides with mesoporous structures have become very hot nanomaterials in the field of supercapacitors owing to their large specific surface areas and suitable pore size distributions. The high specific capacities of these mesoporous metal oxides are resulted from the effective contacts between electrode materials and electrolytes as well as fast transportation of ions and electrons in the bulk of electrode and at the interface of electrode and electrolyte. During the past decade, many achievements on mesoporous transition metal oxides have been made. In this mini-review, we select several typical nanomaterials, such as RuO₂, MnO₂, NiO, Co₃O₄ and nickel cobaltite (NiCo₂O₄), and briefly summarize the recent research progress of these mesoporous transition metal oxides-based electrodes in the field of supercapacitors.

Nickel hydroxide-carbon nanotube nanocomposites as supercapacitor electrodes: crystallinity dependent performances

Nickel hydroxide (Ni(OH)2) is a promising pseudocapacitive material to increase the energy storage capacity of supercapacitors. Ni(OH)2 has three common crystalline structures: amorphous (amor-), α-, and β-Ni(OH)2. There is a lack of good understanding on their pros and cons as supercapacitor electrodes. In this work, we synthesized three nanocomposites with thin layers (10-15 nm) of amor-, α-, and β-Ni(OH)2 deposited on conductive multi-walled carbon nanotubes (MWCNTs). The mass loading of Ni(OH)2 is analogous in these nanocomposites, ranging from 49.1-52.2 wt% with a comparable narrow-pore size distribution centered around 4-5 nm. They were fabricated into supercapacitor electrodes at a mass loading of 6 mg cm(-2) with a thickness of ∼250 μm, similar to the electrodes used in commercial supercapacitors. Our results show that MWCNT/amor-Ni(OH)2 has the highest specific capacitance (1495 or 2984 F g(-1), based on the mass of total active materials or Ni(OH)2 only at the scan rate of 5 mV s(-1) in 1 M KOH electrolyte). It also has the best rate capability among the three nanocomposites. Better performances can be attributed to its disordered structure, which increases its effective surface area and reduces diffusion resistance for redox reactions. However, superior performances gradually deteriorate to the same level as that of MWCNT/β-Ni(OH)2 over 3000 charge/discharge cycles, because amor- and α-Ni(OH)2 transform slowly to more ordered β-Ni(OH)2. Our results highlight that the electrochemical performances of MWCNT/Ni(OH)2 nanocomposites depend on the crystallinity of Ni(OH)2, and the performances of electrodes change upon the crystalline structure transformation of Ni(OH)2 under repeated redox reactions. Future research should focus on improving the structure stability of amor-Ni(OH)2.

NiO-Microflower Formed by Nanowire-weaving Nanosheets with Interconnected Ni-network Decoration as Supercapacitor Electrode

We propose a ‘weaving’ evolution mechanism, by systematically investigating the products obtained in controlled experiments, to demonstrate the formation of Ni-based ‘microflowers’ which consists of multiple characteristic dimensions, in which the three dimensional (3D) NiO ‘microflower’ is constructed by a two-dimensional (2D) nanosheet framework that is derived from weaving one-dimensional (1D) nanowires. We found such unique nanostructures are conducive for the generation of an electrically conductive Ni-network on the nanosheet surface after being exposed to a reducing atmosphere. Our study offers a promising strategy to address the intrinsic issue of poor electrical conductivity for NiO-based materials with significant enhancement of utilization of NiO active materials, leading to a remarkable improvement in the performance of the Ni-NiO microflower based supercapacitor. The optimized Ni-NiO microflower material showed a mass specific capacitance of 1,828 F g⁻¹, and an energy density of 15.9 Wh kg⁻¹ at a current density of 0.5 A g⁻¹. This research not only contributes to understanding the formation mechanism of such ‘microflower’ structures but also offers a promising route to advance NiO based supercapacitor given their ease of synthesis, low cost, and long-term stability.

α-NiS grown on reduced graphene oxide and single-wall carbon nanotubes as electrode materials for high-power supercapacitors

α-NiS combined with SWNTs and graphene exhibits high specific capacitance, and excellent rate performance and cycling stability.

Nanosheet-based hierarchical Ni(2)(CO(3))(OH)(2) microspheres with weak crystallinity for high-performance supercapacitor

Three-dimensionally hierarchical oxide/hydroxide materials have recently attracted increasing interest by virtue of their exciting potential in electrochemical energy conversion and storage. Herein, hierarchical Ni2(CO3)(OH)2 microspheres assembled from ultrathin nanosheets were successfully synthesized by a one-pot/one-step hydrothermal route. In this method, common nickel salts and urea were selected as raw materials. The influence of urea concentration on the final product was studied. The hierarchical Ni2(CO3)(OH)2 microspheres show weak crystallinity and contain crystalline water. It was found that they exhibit excellent rate capacity when used as supercapacitor electrode. Under current density of 0.5 and 10 A/g, the optimized Ni2(CO3)(OH)2 electrode with loading density of 5.3 mg/cm(2) exhibited specific capacitances of 1178 and 613 F/g with excellent cycling stability. The excellent electrochemical property is possibly attributed to the intrinsic nature of Ni2(CO3)(OH)2, the ultrathin thickness of nanosheet units, and the sufficient space available to interact with the electrolyte. This facile synthesis strategy and the good electrochemical properties indicate that hydroxycarbonates are promising materials for supercapacitor application. This study suggests a large library of materials for potential application in energy storage systems.

Recent development of metal hydroxides as electrode material of electrochemical capacitors

Recent research on electrochemical capacitors using transition metal hydroxides as electrode materials is reviewed.

Supercapacitor characteristics of pressurized RuO2/carbon powder as binder-free electrodes

RuO₂/carbon powder electrodes have been designed to be enclosed in a supercapacitor cell and compressed under a constant pressure (4.84 kg_f cm⁻²), which could overcome binder failure under repeated volumetric changes.