Designing 3D highly ordered nanoporous CuO electrodes for high-performance asymmetric supercapacitors

Strategies for Advanced Supercapacitors Based on 2D Transition Metal Dichalcogenides: From Material Design to Device Setup

Recently, the development of new materials and devices has become the main research focus in the field of energy. Supercapacitors (SCs) have attracted significant attention due to their high power density, fast charge/discharge rate, and excellent cycling stability. With a lamellar structure, 2D transition metal dichalcogenides (2D TMDs) emerge as electrode materials for SCs. Although many 2D TMDs with excellent energy storage capability have been reported, further optimization of electrode materials and devices is still needed for competitive electrochemical performance. Previous reviews have focused on the performance of 2D TMDs as electrode materials in SCs, especially on their modification. Herein, the effects of element doping, morphology, structure and phase, composite, hybrid configuration, and electrolyte are emphatically discussed on the overall performance of 2D TMDs-based SCs from the perspective of device optimization. Finally, the opportunities and challenges of 2D TMDs-based SCs in the field are highlighted, and personal perspectives on methods and ideas for high-performance energy storage devices are provided.

Surface-modified CuO nanoparticles for photocatalysis and highly efficient energy storage devices

Herein we report multifunctional surface-modified CuO nanomaterials were used to fulfill escalating needs in the electrochemical energy storage system and to achieve efficient photocatalysts for the degradation of AR88 organic dye. Due to the atom economy, ease of synthesis, high capacitance, observable electrochemical responsiveness, and low bandgap in CuO-based nanomaterials, its active surface was modified through cationic surfactant CTAB. Surface-modified nanoparticles were characterized using various characterization techniques such as XRD, DRS, FESEM, and TEM. Intriguingly the synthesized materials demonstrated a capacitance of 133 F/g with a long-term charge-discharge cycle of 2000 cycles. In addition, at pH 11, the material also exhibited a superior dye degradation performance under the UV lamp by showing 94.8% AR88 degradation at a catalyst concentration of 1.0 g/L. Hence, we believe this concept would provide novel insights into the preparation of the simplest and cheaper multifunctional materials for next-generation energy storage and photocatalytic applications.

Porous Carbon Coated on Cadmium Sulfide-Decorated Zinc Oxide Nanorod Photocathodes for Photo-accelerated Zinc Ion Capacitors

The development of devices with dual solar energy-harvesting and storage functionalities has recently gained significant traction for off-grid power supply. In their most compact embodiment, these devices rely on the same electrode to harvest and store energy; however, in this approach, the development of energy-efficient photoelectrodes with intrinsic characteristics of good optical and electrochemical activities remains challenging. Here, we propose photoelectrodes with a porous carbon coated on a zinc oxide-cadmium sulfide heterostructure as an energy-efficient photocathode for photo-accelerated zinc ion capacitors (Photo-ZICs). The Photo-ZICs harvest light energy and store charge simultaneously, resulting in efficient charge storage performance under illumination compared to dark conditions (∼99% capacity enhancement at 500 mA g^-1 under illumination compared to dark conditions). The light absorption ability and charge separation efficiency achieved by the photocathodes meet the requirements for photo-ZIC applications. Moreover, Photo-ZICs display stable charge storage capacities over long-term cycling, that is, ∼1% capacity loss after 10,000 cycles.

Structural, nonlinear optical and antimicrobial properties of sol-gel derived, Fe-doped CuO thin films

Undoped and Fe-doped CuO thin films with different weight ratios (3, 6, and 9 wt.% of Fe) were deposited onto glass substrates using the sol-gel spin coating technique. X-ray diffraction analysis of these samples indicated that all the films were polycrystalline, and crystallite size decreased with doping concentration. As revealed by scanning electron microscopy, Fe doping increased average particle size and improved size distribution in films. The bandgap of undoped CuO thin film was tuned from 3.48 to 2.79 by the addition of 9 wt.% Fe, and reasonable explanations have been presented. Optical parameters, such as refractive index, extinction coefficient, dielectric constant, and optical conductivity, were calculated for optoelectronic applications. Finally, antimicrobial properties were measured for their possibility to be used as disinfectants, and the antifungal activity of Fe-doped CuO thin films was shown to be more effective.

Fabrication of Zn-Cu-Ni Ternary Oxides in Nanoarrays for Photo-Enhanced Pseudocapacitive Charge Storage

To meet the increasing demands of energy consumption, sustainable energy sources such as solar energy should be better employed to promote electrochemical energy storage. Herein, we fabricated a bifunctional photoelectrode composed of copper foam (CF)-supported zinc-nickel-copper ternary oxides in nanoarrays (CF@ZnCuNiOx NAs) to promote photo-enhanced pseudocapacitive charge storage. The as-fabricated CF@ZnCuNiOx NAs have shown both photosensitive and pseudocapacitive characteristics, demonstrating a synergistic effect on efficient solar energy harvest and conversion. As a result, a high areal specific capacitance of 2741 mF cm−2 (namely 418 μAh cm−2) under light illumination can be calculated at 5 mA cm−2, which delivered photo-enhancement of 38.3% compared to that obtained without light. In addition, the photoelectric and photothermal effects of the light energy on pseudocapacitive charge storage have been preliminarily studied and compared. This work may provide some evidence on the different mechanisms of photoelectric/thermal conversion for developing solar-driven energy storage devices.

CuxO-Modified Nanoporous Cu Foil as a Self-Supporting Electrode for Supercapacitor and Oxygen Evolution Reaction

Designing and modifying nanoporous metal foils to make them suitable for supercapacitor and catalysis is significant but challenging. In this work, Cu_xO nanoflakes have been successfully in situ grown on nanoporous Cu foil via a facile electrooxidation method. A Ga-assisted surface Ga-Cu alloying–dealloying is adopted to realize the formation of a nanoporous Cu layer on the flexible Cu foil. The following electrooxidation, at a constant potential, modifies the nanoporous Cu layer with Cu_xO nanoflakes. The optimum Cu_xO/Cu electrode (O-Cu-2h) delivers the maximum areal capacitance of 0.745 F cm⁻² (410.27 F g⁻¹) at 0.2 mA cm⁻² and maintains 94.71% of the capacitance after 12,000 cycles. The supercapacitor consisted of the O-Cu-2h as the positive electrode and activated carbon as the negative electrode has an energy density of 24.20 Wh kg⁻¹ and power density of 0.65 kW kg⁻¹. The potential of using the electrode as oxygen evolution reaction catalysts is also investigated. The overpotential of O-Cu-2h at 10 mA cm⁻² is 394 mV; however, the long-term stability still needs further improvement.

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, 80CF_hs-20rGO_sp, 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 (rGO_sp) 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.

Facile Fabrication of Polyaniline/Pbs Nanocomposite for High-Performance Supercapacitor Application

In this work, a polyaniline/lead sulfide (PANI/PbS) nanocomposite was prepared by combining the in situ oxidation polymerization method and the surface adsorption process. This nanocomposite was applied as a supercapacitor electrode. The crystal structure, nanomorphology, and optical analysis of PANI and PANI/PbS were investigated. The electrochemical performance of the designed PANI/PbS electrode-based supercapacitor was tested by using cyclic voltammetry (CV), chronopotentiometry (CP), and AC impedance techniques in HCl and Na₂SO₄ electrolytes. The average crystallite size of the PANI/PbS nanocomposite is about 43 nm. PANI/PbS possesses an agglomerated network related to PANI with additional spherical shapes from PbS nanoparticles. After the PANI/PbS nanocomposite formation, there are enhancements in their absorption intensities. At a current density of 0.4 A g⁻¹, the specific capacitance of PANI/PbS in Na₂SO₄ and HCl was found to be 303 and 625 F g⁻¹, respectively. In HCl (625 F g⁻¹ and 1500 mF cm⁻²), the gravimetric and areal capacitances of the PANI/PbS electrode are nearly double those of the Na₂SO₄ electrolyte. Also, the average specific energy and specific power density values for the PANI/PbS electrode in HCl are 4.168 Wh kg⁻¹ and 196.03 W kg⁻¹, respectively. After 5000 cycles, the capacitance loses only 4.5% of its initial value. The results refer to the high stability and good performance of the designed PANI/PbS as a supercapacitor electrode.

Construction of a Cu-Based Metal-Organic Framework by Employing a Mixed-Ligand Strategy and Its Facile Conversion into Nanofibrous CuO for Electrochemical Energy Storage Applications

Recently, metal-organic frameworks (MOFs) have been widely employed as a sacrificial template for the construction of nanostructured materials for a range of applications including energy storage. Herein, we report a facile mixed-ligand strategy for the synthesis of a Cu-MOF, [Cu₃(Azopy)₃(BTTC)₃(H₂O)₃·2H₂O]_n (where BTTC = 1,2,4,5-benzenetetracarboxylic acid and Azopy = 4,4'-azopyridine), via a slow-diffusion method at room temperature. X-ray analysis authenticates the two-dimensional (2D)-layered framework of Cu-MOF. Topologically, this 2D-layered structure is assigned as a 4-connected unimodal net with sql topology. Further, nanostructured CuO is obtained via a simple precipitation method by employing Cu-MOF as a precursor. After analysis of their physicochemical properties through various techniques, both materials are used as surface modifiers of glassy carbon electrodes for a comparative electrochemical study. The results reveal a superior charge storage performance of CuO (244.2 F g^-1 at a current density of 0.8 A g^-1) with a high rate capability compared to Cu-MOF. This observation paves the pathway for the strategic design of high-performing supercapacitor electrode materials.

Gum mediated synthesis and characterization of CuO nanoparticles towards infectious disease-causing antimicrobial resistance microbial pathogens

BACKGROUND

In this work biologically active CuO nanoparticle were discussed. The literature suggests that CuO shows very good antibacterial activity on both Gram positive and Gram-negative bacterial strains. Further, it is used in antibacterial coatings on various substrates to prevent various kinds of medical equipment's. Here CuO NPs was prepared via greener approach and almond gum is used as a reducing agent. Almond gum is nontoxic and contains huge amount of polysaccharides. Hence, the gum mediated CuO NPs can be used to treat urinary tract infection (UTI).

METHOD

The CuO NPs were characterized using UV, FTIR, XRD and HESEM with EDX analysis. The antibacterial (both Gram positive and Gram negative) effects of CuO NPs were determined with agar well diffusion method.

RESULTS

The CuO NPs were characterized by X-ray diffraction pattern result indicates that the monoclinic structure with average crystallite size about 12.91 nm. Straight line model in Scherrer method results found to be crystallite size. The crystallite size and microstrain were estimated in W-H analysis. Lorentz polarization factor, size-strain plot (SSP), morphological index (M-I) and dislocation density were calculated based on x-ray diffraction data. The FTIR analysis confirms presence of Cu and O band. From the absorption spectrum of CuO NPs, it was found to be cutoff wavelength of 230 nm and direct bandgap was found to be 4.97 eV. Morphology analysis shows that the synthesized of CuO NPs reveals agglomerated and spherical in shape. It was found to be 16 nm-25 nm. Energy dispersive spectroscopy (EDX) result indicates percentages of Cu and O element present in the sample. Antimicrobial studies reveal zone of inhibition of CuO NPs. This was used in different pathogens such as gram-positive and Gram-negative bacteria. This study shows exhibit excellent antimicrobial effects of CuO NPs.

CONCLUSION

Hence, in this article the novel and cost-effective method to prepare CuO NPs was discussed. The prepared CuO NPs can be used as an antifungal and antibacterial reagent.

Formation of Copper Oxide Nanotextures on Porous Calcium Carbonate Templates for Water Treatment

The necessity of providing clean water sources increases the demand to develop catalytic systems for water treatment. Good pollutants adsorbers are a key ingredient, and CuO is one of the candidate materials for this task. Among the different approaches for CuO synthesis, precipitation out of aqueous solutions is a leading candidate due to the facile synthesis, high yield, sustainability, and the reported shape control by adjustment of the counter anions. We harness this effect to investigate the formation of copper oxide-based 3D structures. Specifically, the counter anion (chloride, nitrate, and acetate) affects the formation of copper-based hydroxides and the final structure following their conversion into copper oxide nanostructures over porous templates. The formation of a 3D structure is obtained when copper chloride or nitrate reacts with a Sorites scaffold (marine-based calcium carbonate template) without external hydroxide addition. The transformation into copper oxides occurs after calcination or reduction of the obtained Cu₂(OH)₃X (X = Cl⁻ or NO₃⁻) while preserving the porous morphology. Finally, the formed Sorites@CuO structure is examined for water treatment to remove heavy metal cations and degrade organic contaminant molecules.

Electrochemical Performance of Aluminum Doped Ni1−xAlxCo2O4 Hierarchical Nanostructure: Experimental and Theoretical Study

For electrochemical supercapacitors, nickel cobaltite (NiCo2O4) has emerged as a new energy storage material. The electrocapacitive performance of metal oxides is significantly influenced by their morphology and electrical characteristics. The synthesis route can modulate the morphological structure, while their energy band gaps and defects can vary the electrical properties. In addition to modifying the energy band gap, doping can improve crystal stability and refine grain size, providing much-needed surface area for high specific capacitance. This study evaluates the electrochemical performance of aluminum-doped Ni1−xAlxCo2O4 (0 ≤ x ≤ 0.8) compounds. The Ni1−xAlxCo2O4 samples were synthesized through a hydrothermal method by varying the Al to Ni molar ratio. The physical, morphological, and electrochemical properties of Ni1−xAlxCo2O4 are observed to vary with Al3+ content. A morphological change from urchin-like spheres to nanoplate-like structures with a concomitant increase in the surface area, reaching up to 189 m2/g for x = 0.8, was observed with increasing Al3+ content in Ni1−xAlxCo2O4. The electrochemical performance of Ni1−xAlxCo2O4 as an electrode was assessed in a 3M KOH solution. The high specific capacitance of 512 F/g at a 2 mV/s scan rate, 268 F/g at a current density of 0.5 A/g, and energy density of 12.4 Wh/kg was observed for the x = 0.0 sample, which was reduced upon further Al3+ substitution. The as-synthesized Ni1−xAlxCo2O4 electrode exhibited a maximum energy density of 12.4 W h kg−1 with an outstanding high-power density of approximately 6316.6 W h kg−1 for x = 0.0 and an energy density of 8.7 W h kg−1 with an outstanding high-power density of approximately 6670.9 W h kg−1 for x = 0.6. The capacitance retention of 97% and 108.52% and the Coulombic efficiency of 100% and 99.24% were observed for x = 0.0 and x = 0.8, respectively. First-principles density functional theory (DFT) calculations show that the band-gap energy of Ni1−xAlxCo2O4 remained largely invariant with the Al3+ substitution for low Al3+ content. Although the capacitance performance is reduced upon Al3+ doping, overall, the Al3+ doped Ni1−xAlxCo2O4 displayed good energy, powder density, and retention performance. Thus, Al3+ could be a cost-effective alternative in replacing Ni with the performance trade off.

High-performance asymmetric supercapacitor based on CdCO3/CdO/Co3O4 composite supported on Ni foam

A CdCO₃/CdO/Co₃O₄ composite has been prepared on nickel foam through a combined hydrothermal-annealing method. An asymmetric hybrid supercapacitor (SC) device was assembled with this composite as the positive electrode and activated carbon was the negative electrode. The SC exhibited a high specific capacitance of 84 F g⁻¹ @ 1 mA cm⁻², a maximum energy density of 26.3 W h kg⁻¹, and a power density of 2290 W kg⁻¹, along with a wide potential window of 1.5 V and long cycle life (92% after 6000 cycles). SCs assembled in series powered various light-emitting diodes and moved an electrical mini-motor.

This work presents for the first time a CdCO₃/CdO/Co₃O₄@nickel foam based supercapacitor with high both specific capacitance and energy density, a widespread potential window and a long cycle life.

Hierarchical NaFePO4 nanostructures in combination with an optimized carbon-based electrode to achieve advanced aqueous Na-ion supercapacitors

Recent trends in sodium-ion-based energy storage devices have shown the potential use of hollow structures as an electrode material to improve the performance of these storage systems. It is shown that, in addition to the use of hierarchical structures, the choice of the complementary carbon electrode determines the final performance of Na-ion-based devices. Here, we present simple synthesis strategies to prepare different structured carbonaceous materials that can be upscaled to an industrial level. Individual carbon materials deliver specific capacitance ranges from 120 to 220 F g⁻¹ at a current density of 1 A g⁻¹ (with excellent capacity retention). These structures, when combined with hollow NaFePO₄ microspheres to fabricate an aqueous supercapacitor, show as high as a 1.7 V working potential window and can deliver a maximum energy density of 25.29 W h kg⁻¹ capacity retention. These values are much higher than those reported by NaFePO₄ solid particles and randomly chosen carbon structure-based supercapacitors.

An aqueous supercapacitor with hollow NaFePO₄ microsphere structures combined with rGO shows as high as a 1.7 V working potential window and can deliver a maximum energy density of 25.29 W h kg⁻¹ capacity retention.

Indium Tin Oxide Branched Nanowire and Poly(3-hexylthiophene) Hybrid Structure for a Photorechargeable Supercapacitor

We report a photorechargeable supercapacitor that can convert solar energy to chemical energy and store it. The supercapacitor is composed of indium tin oxide branched nanowires (ITO BRs) and poly(3-hexylthiophene) (P3HT) semiconducting polymers. ITO BRs showed electrical double layer capacitive characteristics that originated from the unique porous and self-connected network structure. The hybrid structure of ITO BR/P3HT exhibited spontaneous light harvesting, energy conversion, and charge storage. As a result, photocharging/discharging of ITO BR/P3HT showed an areal capacitance of 2.44 mF/cm² at a current density of 0.02 mA/cm². The proof-of-concept photorechargeable device, composed of ITO BRs, ITO BR/P3HT, and Na₂SO₄/polyvinyl acetate gel electrolyte, generated a photovoltage as high as 0.28 V and stored charge effectively for tens of seconds. The combination of dual functions in a single hybrid material may achieve breakthrough advances.

Rational design of flower-like Co-Zn LDH@Co(H2PO4)2 heterojunctions as advanced electrode materials for supercapacitors

Layered double hydroxides (LDHs) with high theoretical specific capacity have been considered as one of the most promising candidates for high-performance supercapacitors. However, the low electronic conductivity and insufficient active sites hinder the further large-scale application of bulk LDHs. Here, we successfully synthesized heterostructured Co-Zn LDH@Co(H₂PO₄)₂ nanoflowers by a simple hydrothermal method. As the amount of Co(H₂PO₄)₂ in the whole heterostructure increases, the nanosheets steadily evolve into nanoflowers with a high surface area, providing more electrochemically active sites. Moreover, the built-in electric field formed between Co-Zn LDH and Co(H₂PO₄)₂ improves the conductivity of the composite electrode. As a result, the as-prepared Co-Zn LDH@Co(H₂PO₄)₂ shows a high specific capacity of 919 C g^-1 at a current density of 1 A g^-1. A hybrid supercapacitor (HSC) with activated carbon (AC) as the negative electrode and Co-Zn LDH@Co(H₂PO₄)₂ as the positive electrode delivers an energy density of 30.4 W h kg^-1 at a power density of 400 W kg^-1, and 95.3% of the initial capacity is retained after 5000 cycles. This study provides a novel synthesis strategy for constructing heterojunctions to enhance the energy storage properties of LDH-based materials.

Construction of hierarchical sea urchin-like manganese substituted nickel cobaltite@tricobalt tetraoxide core-shell microspheres on nickel foam as binder-free electrodes for high performance supercapacitors

Construction of binder-free electrodes with hierarchical core-shell nanostructures is considered to be an effective route to promote the electrochemical performance of supercapacitors. In this work, the porous Ni_0.5Mn_0.5Co₂O₄ nanoflowers anchored on nickel foam are utilized as framework for further growing Co₃O₄ nanowires, resulting in the hierarchical sea urchin-like Ni_0.5Mn_0.5Co₂O₄@Co₃O₄ core-shell microspheres on nickel foam. Owing to the advantages brought by unique porous architecture and synergistic effect of the multi-component composites, the as-prepared electrode exhibits a high specific capacitance (931 F/g at 1 A/g), excellent rate performance (77% capacitance retention at 20 A/g) and outstanding cycle stability (92% retention over 5000 cycles at 5 A/g). Additionally, the assembled Ni_0.5Mn_0.5Co₂O₄@Co₃O₄//AC (activated carbon) asymmetric supercapacitor achieves a high energy density (50 Wh/kg at 750 W/kg) and long durability (88% retention after 5000 cycles).

Flexible Free-Standing MoO3/Ti3C2T z MXene Composite Films with High Gravimetric and Volumetric Capacities

Enhancing both the energy storage and power capabilities of electrochemical capacitors remains a challenge. Herein, Ti3C2T z MXene is mixed with MoO3 nanobelts in various mass ratios and the mixture is used to vacuum filter binder free, open, flexible, and free-standing films. The conductive Ti3C2T z flakes bridge the nanobelts, facilitating electron transfer; the randomly oriented, and interconnected, MoO3 nanobelts, in turn, prevent the restacking of the Ti3C2T z nanosheets. Benefitting from these advantages, a MoO3/Ti3C2T z film with a 8:2 mass ratio exhibits high gravimetric/volumetric capacities with good cyclability, namely, 837 C g-1 and 1836 C cm-3 at 1 A g-1 for an ≈ 10 µm thick film; and 767 C g-1 and 1664 C cm-3 at 1 A g-1 for ≈ 50 µm thick film. To further increase the energy density, hybrid capacitors are fabricated with MoO3/Ti3C2T z films as the negative electrodes and nitrogen-doped activated carbon as the positive electrodes. This device delivers maximum gravimetric/volumetric energy densities of 31.2 Wh kg-1 and 39.2 Wh L-1, respectively. The cycling stability of 94.2% retention ratio after 10 000 continuous charge/discharge cycles is also noteworthy. The high energy density achieved in this work can pave the way for practical applications of MXene-containing materials in energy storage devices.

Calcination Strategy for Scalable Synthesis of Pithecellobium-Type Hierarchical Dual-Phase Nanostructured Cu x O to Columnar Self-Assembled CuO and Its Electrochemical Performances

The search for low-cost environmentally benign promising electrode materials for high-performance electrochemical application is an urgent need for an applaudable solution for the energy crisis. For this, the present attempt has been made to develop a scalable synthetic strategy for the preparation of pure and dual-phase copper oxide self-hybrid/self-assembled materials from a copper oxalate precursor using the calcination route. The obtained samples were characterized by means of various physicochemical analytical techniques. Notably, we found that the BET surface area and pore volume of copper oxides measured by N2 adsorption-desorption decrease with the elevation of calcination temperature. From the XRD analysis, we observed the formation of a Cu2O cubic phase at low temperatures and a CuO monoclinic phase at high temperatures (i.e., 450 and 550 °C). FTIR and RAMAN spectroscopy were employed for bonding and vibrational structure analysis. The self-assembled dual-phase copper oxide particle as a pithecellobium-type hierarchical structure was observed through SEM of the sample prepared at 350 °C. The surface morphological structure for the samples obtained at 450 and 550 °C was a bundle-like structure developed though columnar self-assembling of the particles. All the above techniques confirmed the successful formation of Cu2O/CuO nanoparticles. Afterward, the electrochemical properties of the as-synthesized copper oxides reinforced by introducing carbon black (10% wt) were explored via cyclic voltammetry, electrochemical impedance spectroscopy, and galvanometric charge-discharge analysis. The Cu2O system exhibits the maximum specific capacitance performance value of 1355 F/g, whereas in the CuO system (at 450 and 550 °C), it possesses values of 903 and 724 F/g at a scan rate of 2 mV/s. This study reveals that the electrochemical properties of Cu2O are better than those of the CuO nanoparticles, which could be ascribed to the high surface area and morphology. The present assessment of the electrochemical properties of the developed material could pave the way to a low-cost electrode material for developing other high-performance hybrid electrodes for supercapacitor or battery applications.

The Optical and Electrical Performance of CuO Synthesized by Anodic Oxidation Based on Copper Foam

Metal oxide semiconductor materials have a wide range of applications in the field of solar energy conversion. In this paper, CuO was prepared directly on copper foam substrate by anodic oxidation. The effects of current density and anodizing temperature on sample preparation and performance were studied. Field emission scanning electron microscopy (FESEM) and X-ray diffractometer (XRD) had been used to determine the morphology and phase structure of the sample, and its optical and electrical properties were discussed through UV-vis spectrophotometer and electrochemical tests. In addition, the influences of experimental conditions such as current density and reaction temperature on the morphology and properties of CuO were systematically discussed. The FESEM images showed that as the anodic oxidation temperature increase, the morphology of the prepared sample changed from nanowires to leaf-like CuO nanosheets. According to the results of XRD, the structure of prepared CuO was monoclinic, and the intensity of diffraction peaks gradually increased as anodizing temperature increased. We found that the optimum current density and anodizing temperature were 20 mA cm⁻² and 60 °C, respectively. The results of electrochemical indicated that the CuO electrode based on copper foam (CuO/Cu foam) prepared at the optimum exhibited the highest specific capacitance (0.1039 F cm⁻²) when the scan rate was 2 mV s⁻¹.

In Situ Growth of 2D Ultrathin NiCo2 O4 Nanosheet Arrays on Ni Foam for High Performance and Flexible Solid-State Supercapacitors

In order to further overcome the shortage of electrodes with additive/binder and modulate the structure of NiCo₂ O₄ for supercapacitors, ultrathin NiCo₂ O₄ nanosheet arrays have been in situ grown on Ni foam by optimizing hydrothermal reactions based on crystal growth dynamics. The structure of ultrathin NiCo₂ O₄ nanosheet arrays can expose more active sites, provide abundant diffusion channels and buffer the stress caused by phase transition during charge-discharge process of supercapacitors. The optimized hydrothermal reactions can provide more ordered crystal orientations by keeping nanosheets on Ni foam completely coming from in situ growth, which will decrease the inner resistance of ultrathin NiCo₂ O₄ nanosheets and improve the efficiency and kinetics of electrons transfer. By the virtue of such remarkable features, the electrochemical results confirm the rationality of structural modulation and crystal orientations optimization with a drastically enhanced specific capacitance of 2017.8 F g^-1 , admirable rate performance of 93.2% and outstanding stability retention of 90.9% after cycling 5000 times. More impressively, the assembled flexible solid-state asymmetric supercapacitor (ASC) shows superior energy density, power density, and high stability. The modification strategy in this paper may throw light on the rational design of new generation advanced electrode materials for high-performance flexible supercapacitors.

Synthesis of nickel-copper composite with controllable nanostructure through facile solvent control as positive electrode for high-performance supercapacitors

The surface characteristics of electrodes vary depending on the solvent used. Furthermore, electrochemical performance varies depending on the surface morphology of the electrode. In this study, we grew 3D binary NiCu-based composites on Ni foam, via a binder-free hydrothermal method, for use as a cathode in high-performance supercapacitors. We employed different solvents to prepare the electrodes by adjusting the ratio of deionized water (DI water) to methanol. The electrode prepared using DI water as the solvent had the largest surface area with a nanowire structure. This morphology allowed for good electrical performance by greatly improving the electrode and electrolyte contact area and shortening the ion diffusion path. The optimized deposition of NiCu(CO₃)(OH)₂ nanowires (50 mL of DI water as solvent) showed an excellent maximum specific capacity of 758.9 mA h g^-1 at a current density of 3 A g^-1, as well as outstanding cycling performance with 87.2% retention after 5000 cycles. In this work, we focused on the large specific surface area and suitable electrochemical properties of NiCu(CO₃)(OH)₂ electrodes with various solvents. As a result, the asymmetric supercapacitor (ASC) using the NiCu(CO₃)(OH)₂ electrode prepared with 50 ml of DI water as the solvent as the positive electrode and graphene as the negative electrode, exhibited an energy density of 26.7 W h kg^-1 at a power density of 2534 W kg^-1, and excellent cycling stability with 91.3% retention after 5000 cycles. The NiCu(CO₃)(OH)₂//graphene ASC could turn on an LED light and demonstrated better electrical performance than most previously reported nickel- and copper-based carbonate hydroxide ASCs. In addition, in the present scenario where many nanoscale studies are conducted, a method of controlling the nanostructure of a material through facile solvent control will be of great help to many researchers.

Synthesis of CoO-Decorated Graphene Hollow Nanoballs for High-Performance Flexible Supercapacitors

The formation of thin and uniform capacitive layers for fully interacting with an electrolyte in a supercapacitor is a key challenge to achieve optimal capacitance. Here, we demonstrate a binder-free and flexible supercapacitor with the electrode made of cobalt oxide nanoparticle (CoO NP)-wrapped graphene hollow nanoballs (GHBs). The growth process of Co(OH)₂ NPs, which could subsequently be thermally annealed to CoO NPs, was monitored by in situ electrochemical liquid transmission electron microscopy (TEM). In the dynamic growth of Co(OH)₂ NPs on a film of GHBs, the lateral formation of fan-shaped clusters of Co(OH)₂ NPs spread over the surface of GHBs was observed by in situ TEM. This CoO-GHBs/CC electrode exhibits high specific capacitance (2238 F g^-1 at 1 A g^-1) and good rate capability (1170 F g^-1 at 15 A g^-1). The outstanding capacitive performance and good rate capability of the CoO-GHBs/CC electrode were achieved by the synergistic combination of highly pseudocapacitive CoO and electrically conductive GHBs with large surface areas. A solid-state symmetric supercapacitor (SSC), with CoO-GHBs/CCs used for both positive and negative electrodes, exhibits high power density (6000 W kg^-1 at 8.2 Wh kg^-1), high energy density (16 Wh kg^-1 at 800 W kg^-1), cycling stability (∼100% capacitance retention after 5000 cycles), and excellent mechanical flexibility at various bending positions. Finally, a serial connection of four SSC devices can efficiently power a red light-emitting diode after being charged for 20 s, demonstrating the practical application of this CoO-GHBs/CC-based SSC device for efficient energy storage.

Synthesis of Cu-Doped Mn3O4@Mn-Doped CuO Nanostructured Electrode Materials by a Solution Process for High-Performance Electrochemical Pseudocapacitors

Cu-doped Mn3O4 and Mn-doped CuO (CMO@MCO) mixed oxides with isolated phases together with pristine Mn3O4 (MO) and CuO (CO) have been synthesized by a simple solution process for applications in electrochemical supercapacitors. The crystallographic, spectroscopic, and morphological analyses revealed the formation of all of the materials with good crystallinity and purity with the creation of rhombohedral-shaped MO and CMO and a mixture of spherical and rod-shaped CO and MCO nanostructures. The ratio of CMO and MCO in the optimized CMO@MCO was 2:1 with the Cu and Mn dopants percentages of 12 and 15%, respectively. The MO-, CO-, and CMO@MCO-modified carbon cloth (CC) electrodes delivered the specific capacitance (C s) values of 541.1, 706.7, and 997.2 F/g at 5 mV/s and 413.4, 480.5, and 561.1 F/g at 1.3 A/g, respectively. This enhanced C s value of CMO@MCO with an energy density and a power density of 78.0 Wh/kg and 650.0 W/kg, respectively, could be attributed to the improvement of electrical conductivity induced by the dopants and the high percentage of oxygen vacancies. This corroborated to a decrease in the optical band gap and charge-transfer resistance (R ct) of CMO@MCO at the electrode/electrolyte interface compared to those of MO and CO. The net enhancement of the Faradaic contribution induced by the redox reaction of the dopant and improved surface area was also responsible for the better electrochemical performance of CMO@MCO. The CMO@MCO/CC electrode showed high electrochemical stability with a C s loss of only ca. 4.7%. This research could open up new possibilities for the development of doped mixed oxides for high-performance supercapacitors.

Nanochannels regulating ionic transport for boosting electrochemical energy storage and conversion: a review

Electrochemical power sources, as one of the most promising energy storage and conversion technologies, provide great opportunities for developing high energy density electrochemical devices and portable electronics. However, uncontrolled ionic transport in electrochemical energy conversion, typically undesired anion transfer, usually causes some issues degrading the performance of energy storage devices. Nanochannels offer an effective strategy to solve the ionic transport problems for boosting electrochemical energy storage and conversion. In this review, the advantages of nanochannels for electrochemical energy storage and conversion and the construction principle of nanochannels are introduced, including ion selectivity and ultrafast ion transmission of nanochannels, which are considered as two critical factors to achieve highly efficient energy conversion. Recent advances in applications of nanochannels in lithium secondary batteries (LSBs), electrokinetic energy conversion systems and concentration cells are summarized in detail. Nanochannels exist in the above systems in two typical forms: functional separator and electrode protective layer. Current research on nanochannel-based LSBs is still at the early stage, and deeper and broader applications are expected in the future. Finally, the remaining challenges of nanochannel fabrication, performance improvement, and intelligent construction are presented. It is envisioned that this paper will provide new insights for developing high-performance and versatile energy storage electronics based on nanochannels.

Snowflake-Like Dendritic CoNi Alloy-rGO Nanocomposite as a Cathode Electrode Material for an All-Solid-State Flexible Asymmetric High-Performance Supercapacitor Device

Flexible all-solid-state supercapacitors having high mechanical stability and foldable features are crucial to meet the growing demands for a large number of portable electronic devices such as wearable electronics, displays, touch screens, detectors, etc. Here, we report the fabrication of such a flexible all-solid-state asymmetric supercapacitor device by using a nanocomposite composed of a snowflake-like dendritic CoNi alloy and reduced graphene oxide ((CoNi_D)₆₀-rGO₄₀) as the positive electrode and pure rGO as the negative electrode for the first time. In this device, a polyvinyl alcohol (PVA) gel containing 3 M KOH and 0.1 M K₄[Fe(CN)₆] was used as the electrolyte cum separator. This supercapacitor device offers a high energy density value of 52.8 Wh kg^-1 at a power density of 2000 W kg^-1. The values of these two key performance parameters are superior to the many commercially available supercapacitors and reported values in the literature. In addition, this device also exhibits retention of ∼95% of its initial specific capacitance value after 4000 cycles at a current density of 2.5 A g^-1, displaying its high cycling stability. This supercapacitor is so flexible that no mechanical deformation occurs even after bending at different angles and folding up to 180°, and its specific capacitance value practically remains unaffected when the device was twisted at different bending angles. This flexible all-solid-state asymmetric supercapacitor device can power a light-emitting diode (LED) and demonstrates its promise to meet the practical applications in energy storage technology.

Energetic Cost for Being "Redox-Site-Rich" in Pseudocapacitive Energy Storage with Nickel-Aluminum Layered Double Hydroxide Materials

Defining the energetic landscape of pseudocapacitive materials such as transition metal layered double hydroxides (LDHs) upon redox-site enrichment is essential to harnessing their power for effective energy storage. Here, coupling acid solution calorimetry, in situ XRD, and in situ DRIFTS, we demonstrate that as the Ni/Al ratio increases, both as-made (hydrated) and dehydrated NiAl-LDH samples are less stable as evidenced by their enthalpies of formation. Moreover, the higher specific capacity at an intermediate Ni/Al ratio of 3 is enabled by effective water-LDH interactions, which energetically stabilize the excessive near-surface Ni redox sites, solvate intercalated carbonate ions, and fill the expanded vdW gap, paying for the "energetic cost" of being "redox-site-rich". Thus, from a thermodynamic perspective, engineering molecule/solid-LDH interactions on the nanoscale with confined guest species other than water, which energetically impose stronger stabilization, may help us to achieve their specific capacitance potential.

Simple pyrolysis of alginate-based hydrogel cross-linked by bivalent ions into highly porous carbons for energy storage

Searching for a sustainable precursor that is capable of absorbing microwave energy is crucial for its rapid conversion into porous carbon via microwave heating. Here, alginate-based hydrogel beads cross-linked by bivalent ions (Cu2+, Zn2+, and Ca2+) are converted into porous carbons (SPCs) in 10 min by applying simple microwave-assisted pyrolysis. Water wrapped in hydrogel beads and bivalent ions serve as initial microwave absorbers to convert alginate into char which acts as a good microwave absorber in the following stages. Additionally, bivalent ions also act as a gelling agent to generate hydrogel beads, as a porogen to obtain a highly porous structure, and as a metal donor to form the SPC/Cu composite. The resultant SPC has a high specific surface area of 1336 m2 g-1, a large total pore volume of 0.56 cm3 g-1, interconnected macropores, as well as a high oxygen content of up to 13.2%. These attractive characteristics give SPC a remarkable rate capability of 72% at 50 A g-1. Interestingly, the interconnected macropores in SPC offer sufficient space for Cu growth via the redox reactions of Cu2+; thus, the SPC/Cu composite without acid wash shows a specific capacitance as high as 804 F g-1 at 0.5 A g-1.

Recent Advances in Fiber Supercapacitors: Materials, Device Configurations, and Applications

Fiber supercapacitors (SCs), with their small size and weight, excellent flexibility and deformability, and high capacitance and power density, are recognized as one of the most robust power supplies available for wearable electronics. They can be woven into breathable textiles or integrated into different functional materials to fit curved surfaces for use in day-to-day life. A comprehensive review on recent important development and progress in fiber SCs is provided, with respect to the active electrode materials, device configurations, functions, integrations. Active electrode materials based on different electrochemical mechanisms and intended to improve performance including carbon-based materials, metal oxides, and hybrid composites, are first summarized. The three main types of fiber SCs, namely parallel, twist, and coaxial structures, are then discussed, followed by the exploration of some functions including stretchability and self-healing. Miniaturized integration of fiber SCs to obtain flexible energy fibers and integrated sensing systems is also discussed. Finally, a short conclusion is made, combining with comments on the current challenges and potential solutions in this field.

Formation of graphene-wrapped multi-shelled NiGa2O4 hollow spheres and graphene-wrapped yolk-shell NiFe2O4 hollow spheres derived from metal-organic frameworks for high-performance hybrid supercapacitors

To construct a supercapacitor (SC) with considerable performance, synthesis of an electrode material with a highly porous structure is necessary. Herein, an efficient metal-organic framework (MOF)-derived procedure is offered to construct a graphene wrapped multi-shelled NiGa2O4 hollow sphere (GW-MSNGOHS) positive electrode material and a graphene-wrapped yolk-shell NiFe2O4 hollow sphere (GW-YS-NFOHS) negative electrode material with a highly porous nature in SCs. The GW-MSNGOHS and GW-YS-NFOHS electrodes exhibit excellent capacities (∼411.25 mA h g-1 and 254.25 mA h g-1, respectively, at 1 A g-1), reasonable rate performances (75.85%, and 62.7%, respectively), and outstanding cyclability (98.9% and 90.9%, respectively). Benefiting from the reasonably engineered negative and positive electrodes, the fabricated asymmetric device (GW-MSNGOHS//GW-YS-NFOHS) can show an excellent energy density (ED) of 118.97 W h kg-1 at a power density (PD) of 1702 W kg-1, an exceptional robustness of 92.1%, and an excellent capacity (Cs) of 140.2 mA g-1.

Cobalt/Nickel Ions-Assisted Synthesis of Laminated CuO Nanospheres Based on Cu(OH)2 Nanorod Arrays for High-Performance Supercapacitors

The development for environmentally friendly energy conversion and storage equipment has given rise to tremendous research efforts as a result of the growing requirements for environmental friendly resources and the rapid consumption of traditional fossil fuel. Herein, a novel hierarchical CoO/NiO-Cu@CuO heterostructure is successfully devised and synthesized. Cobalt/nickel ions are used to generate novel CoO/NiO-doped laminated CuO nanospheres through the facile in situ wet oxidation combined with cation exchange and calcination strategies. As a result, the electrochemical supercapacitance of the as-prepared CoO/NiO-Cu@CuO electrode can reach 875 C cm^-2 (2035 mF cm^-2), which exhibits much better electrochemical performance compared to other precursor electrodes at a same current density of 2 mA cm^-2. Moreover, an excellent rate capacity of 1395 mF cm^-2 (50 mA cm^-2) can be achieved when measured at a relative high current density; 90.3% of the initial supercapacitance remains even after 5000 cycles. Furthermore, the as-prepared hierarchical hybrid of laminated CoO/NiO-CuO nanospheres in situ generated on three-dimensional (3D) porous Cu foam is applied to prepare a solid-state asymmetric supercapacitor equipment unit. The fabricated equipment unit shows an energy density of 69.3 W h kg^-1 at a power density of 1080 W kg^-1. Additionally, the commercially applied 2.5 V light-emitting-diode indicator with blue light can be energized for 4 min when two as-fabricated supercapacitor devices are in series connection. The unique hierarchical heterostructure of the novel laminated nanospheres combined with the 3D grid structure brings about the outstanding electrochemical capacitor performances. This strategy for the fabrication of hierarchical heterostructure electrodes could have an enormous potential for high-performance electrochemical equipment.

Metal oxide-based supercapacitors: progress and prospectives

Distinguished by particular physical and chemical properties, metal oxide materials have been a focus of research and exploitation for applications in energy storage devices. Used as supercapacitor electrode materials, metal oxides have certified attractive performances for fabricating various supercapacitor devices in a broad voltage window. In comparison with single metal oxides, bimetallic oxide materials are highly desired for overcoming the constraint of the poor electric conductivity of single metal oxide materials, achieving a high capacitance and raising the energy density at this capacitor-level power. Herein, we investigate the principal elements affecting the properties of bimetallic oxide electrodes to reveal the relevant energy storage mechanisms. Thus, the influences of the chemical constitution, structural features, electroconductivity, oxygen vacancies and various electrolytes in the electrochemical behavior are discussed. Moreover, the progress, development and improvement of multifarious devices are emphasized systematically, covering from an asymmetric to hybrid configuration, and from aqueous to non-aqueous systems. Ultimately, some obstinate and unsettled issues are summarized as well as a prospective direction has been given on the future of metal oxide-based supercapacitors.