Preparation and electrochemical performances of carbon sphere@ZnO core-shell nanocomposites for supercapacitor applications

Electrocatalysis of Oxygen Evolution Reaction Promoted by CoNiMn Films Synthesized by Electrodeposition

Recently, efforts have been made to address the environmental damage caused by fossil-fuel-based primary energy sources. Interest in efficient technologies for converting and storing energy using renewable sources, especially sunlight, has increased, with the aim of replicating the natural photosynthesis process. However, artificial photosynthesis faces challenges with unfavorable kinetics and thermodynamics, requiring the use of stable catalysts for the hydrogen evolution (HER) and oxygen evolution (OER) reactions to generate H2 and O2, respectively. OER is the most prohibitive of the half-reactions by the highly sluggish kinetics. Mixed oxides, particularly those based on first-row transition metals, have shown promising results as catalysts for the OER. This work reports the synthesis of CoNiMn oxide via electrodeposition on fluoride tin oxide followed by electrochemical activation. This approach seeks to explore the synergistic effect between the elements and to produce a catalyst with superior efficiency and stability for the electrocatalysis of the OER compared to the monometallic and bimetallic oxides. The CoNiMn film was structurally and electrochemically characterized. The electrodeposited CoNiMn hybrid films demonstrated low overpotentials compared with standard OER electrocatalysts, with CoNiMn films outperforming all single and bimetallic oxide films. The activated CoNiMn film required an overpotential of 100 mV at 10 mA cm-2 (430 mV at 25 mA cm-2) and Tafel slope of 58 mV dec-1. The film was active for 15 h at 100 mA cm-2 and showed no significant change in morphology and structure after the chronopotentiometry, indicating that it is a promising and cost-effective alternative to enhance the OER activity using abundant elements.

Understanding the Behavior of Supercapacitor Materials via Electrochemical Impedance Spectroscopy: A Review

Energy harvesting and energy storage are two critical aspects of supporting the energy transition and sustainability. Many studies have been conducted to achieve excellent performance devices for these two purposes. As energy-storing devices, supercapacitors (SCs) have tremendous potential to be applied in several sectors. Some electrochemical characterizations define the performance of SCs. Electrochemical impedance spectroscopy (EIS) is one of the most powerful analyses to determine the performance of SCs. Some parameters obtained from this analysis include bulk resistance, charge-transfer resistance, total resistance, specific capacitance, response frequency, and response time. This work provides a holistic and comprehensive review of utilizing EIS for SC characterization. Overall, researchers can benefit from this review by gaining a comprehensive understanding of the utilization of electrochemical impedance spectroscopy (EIS) for characterizing supercapacitors (SCs), enabling them to enhance SC performance and contribute to the advancement of energy harvesting and storage technologies.

Synthesis of Zinc Oxide Nanorods from Zinc Borate Precursor and Characterization of Supercapacitor Properties

The synthesis of zinc oxide (ZnO) was accomplished from zinc borate (Zn3B2O6) minerals to be used as electrodes in supercapacitor applications. The concentrations of obtained zinc (Zn) metal after treatment with hydrochloric acid (HCl) were determined by atomic absorption spectroscopy (AAS). Direct synthesis of ZnO on a nickel (Ni) foam surface was conducted by employing the hydrothermal technique using a solution with the highest Zn content. The results showed the successful synthesis of ZnO nanorods on the surface of Ni foam with an average wall size of approximately 358 nm. Cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) measurements revealed that the synthesized electrode exhibited battery-type charge storage characteristics, reaching a maximum specific capacitance of approximately 867 mF·cm-² at a current density of 2 mA·cm-². Additionally, the energy and power densities of the electrode at a current density of 2 mA·cm-² were calculated as 19.3 mWh·cm-² and 200 mW·cm-², respectively. These results exhibited promising performance of the single-component electrode, outperforming the existing counterparts reported in the literature.

Fabrication of Robust and Stable N-Doped ZnO/Single-Walled Carbon Nanotubes: Characterization, Photocatalytic Application, Kinetics, Degradation Products, and Toxicity Analysis

The production of effective visible-light (VL) photocatalysts for the elimination of noxious organic pollutants from wastewater has attracted considerable interest owing to increasing awareness worldwide. Despite the large number of photocatalysts reported, the selectivity and activity of photocatalysts still need to be developed. The goal of this research is to eliminate toxic methylene blue (MB) dye from wastewater through a cost-effective photocatalytic process using VL illumination. A novel N-doped ZnO/carbon nanotube (NZO/CNT) nanocomposite was successfully synthesized via a facile cocrystallization method. The structural, morphological, and optical properties of the synthesized nanocomposite were systematically investigated. The as-prepared NZO/CNT composite exhibited remarkable photocatalytic performance (96.58%) within 25 min of VL irradiation. The activity was 92, 52, and 27% greater than that of photolysis, ZnO, and NZO, respectively, under identical conditions. The enhanced photocatalytic efficiency of NZO/CNT was attributed to the N atom and CNT involvement: N contributes to narrowing the band gap of ZnO, and CNT captures the electrons and maintains the electron flow in the system. The reaction kinetics of MB degradation, catalyst reusability, and stability were also investigated. In addition, the photodegradation products and their toxicity effects in our environment were analyzed using the liquid chromatography-mass spectrometry and ecological structure activity relationships programs, respectively. The findings of the current study demonstrate that the NZO/CNT nanocomposite can be utilized to remove contaminants in an environmentally acceptable manner, thereby providing a new window for practical applications.

Organoamine Templated Multifunctional Hybrid Metal Phosphonate Frameworks: Promising Candidates for Tailoring Electrochemical Behaviors and Size-Selective Efficient Heterogeneous Lewis Acid Catalysis

The successful discovery of novel multifunctional metal phosphonate framework materials that incorporate newer organoamines and their utilization as a potential electroactive material for energy storage applications (supercapacitors) and as efficient heterogeneous catalysts are the most enduring challenges at present. From this perspective, herein, four new inorganic-organic hybrid zinc organodiphosphonate materials, namely, [C₅H₁₄N₂]₂[Zn₆(hedp)₄] (I), [C₅H₁₄N₂]_0.5[Zn₃(Hhedp) (hedp)]·2H₂O (II), [C₆H₁₆N₂][Zn₃(hedp)₂] (III), and [C₁₀H₂₄N₄][Zn₆(Hhedp)₂(hedp)₂] (IV) (H₄hedp = 1-hydroxyethane 1,1-diphosphonic acid), have been synthesized through the introduction of different organoamines and then structurally analyzed using various techniques. The compounds (I-IV) possess a three-dimensional network through alternate connectivity of zinc ions and diphosphonate ligands, as confirmed using single-crystal X-ray diffraction. The investigations of electrochemical charge storage behaviors of the present compounds indicate that compound III exhibits a high specific capacitance of 190 F g^-1 (76 C g^-1) at 1 A g^-1, while compound II shows an excellent cycling stability of 90.11% even after 5000 cycles at 5 A g^-1 in the 6 M KOH solution. Further, the present materials have also been utilized as active heterogeneous Lewis acid catalysts in the ketalization reaction. The screening of various substrate scopes during the catalytic process confirms the size-selective heterogeneous catalytic nature of the framework compounds. To our utmost knowledge, such a size-selective heterogeneous Lewis acid catalytic behavior has been observed for the first time in the amine templated inorganic-organic hybrid framework family. Moreover, the excellent size-selective catalytic efficiencies with the d¹⁰ metal system and recyclability performances make the compounds (I-IV) more efficient and promising Lewis acid heterogeneous catalysts.

Fabrication and application of a novel electrochemical biosensor based on a mesoporous carbon sphere@UiO-66-NH2/Lac complex enzyme for tetracycline detection

The overuse of tetracycline results in a threat to human, poultry and livestock health. An enzymatic electrochemical biosensor is an ideal alternative method for accurate and rapid tetracycline detection, while the unstable and easily deactivated nature of the enzyme limits its development. To overcome these limitations, a highly sensitive enzymatic electrochemical biosensor for the determination of tetracycline is developed in this work based on a complex enzyme which was constructed using a mesoporous carbon sphere@UiO-66-NH2 (MCS@UiO-66-NH2) core-shell composite with embedded laccase (Lac). Compared to pure MCS and UiO-66-NH2, the MCS@UiO-66-NH2 core-shell composite has an advantageous mesoporous structure (pore diameter >8 nm), which is suitable for the immobilization of small laccase. The biosensor based on the complex enzyme exhibits a superior activity and enhanced stability as compared with that made using a pure enzyme because the mesoporous structure of the MCS@UiO-66-NH2 composite can effectively protect the laccase against inactivation and denaturation. Besides, its high specific surface area and good conductivity are beneficial to enzyme immobilization and electron transfer in the modified electrode. The biosensor based on this complex enzyme exhibits a relatively low detection limit of 8.94 × 10-7 mol L-1 and a detection range of 1.0 × 10-6-6.0 × 10-5 mol L-1 for tetracycline detection. Furthermore, the developed biosensor possesses good long-term stability, selectivity and reproducibility, indicating its potential application for tetracycline determination in actual food. This research work provides a prospective solution to resolve the stability and inactivation problems of enzymatic electrochemical biosensors in different application scenarios.

Integrated hybrid architecture of metal and biochar for high performance asymmetric supercapacitors

Two state-of-the-art electrodes were successfully synthesized and used to assemble both symmetric and asymmetric type supercapacitors. 3DFAB was fabricated by direct pyrolysis of green macroalgae in the presence of NaOH. Possible NaOH activation mechanisms are proposed, which explains the formation of oxygen functional groups through quick penetration of OH- and NaOH into the vacancies. To obtain CoTLM, the tile-like architecture of cobalt oxides was introduced to the 3D interconnected functional algal biochar (3DFAB) by a simple one-pot hydrothermal method under mild conditions. For the symmetric supercapacitors, the maximum specific capacitance of RAB, 3DFAB, and CoTLM were 158, 296, and 445 F g^-1 at the current density of 1 A g^-1. Regarding cobalt-based asymmetric systems, the maximum capacitance for the 3DFAB//CoTLM was 411 F g^-1. This asymmetric supercapacitor device also retained 100.9% of its initial capacitance after 4000 cycles at the current density of 4 A g^-1. Unbuffered aqueous electrolyte and the unique morphological structure used in this study might catapult forward commercialization of such advanced energy storage devices.

Preparation of NiO decorated CNT/ZnO core-shell hybrid nanocomposites with the aid of ultrasonication for enhancing the performance of hybrid supercapacitors

Supercapacitor (SC) electrodes fabricated with the combination of carbon nanotubes (CNTs) and metal oxides are showing remarkable advancements in the electrochemical properties. Herein, NiO decorated CNT/ZnO core-shell hybrid nanocomposites (CNT/ZnO/NiO HNCs) are facilely synthesized by a two-step solution-based technique for the utilization in hybrid supercapacitors. Benefitting from the synergistic advantages of three materials, the CNT/ZnO/NiO HNCs based electrode has evinced superior areal capacity of ~67 µAh cm-2 at a current density of 3 mA cm-2 with an exceptional cycling stability of 112% even after 3000 cycles of continuous operation. Highly conductive CNTs and electrochemically active ZnO contribute to the performance enhancement. Moreover, the decoration of NiO on the surface of CNT/ZnO core-shell increases the electro active sites and stimulates the faster redox reactions which play a vital role in augmenting the electrochemical properties. Making the use of high areal capacity and ultra-long stability, a hybrid supercapacitor (HSC) was assembled with CNT/ZnO/NiO HNCs coated nickel foam (CNT/ZnO/NiO HNCs/NF) as positive electrode and CNTs coated NF as negative electrode. The fabricated HSC delivered an areal capacitance of 287 mF cm-2 with high areal energy density (67 µWh cm-2) and power density (16.25 mW cm-2). The combination of battery type CNT/ZnO/NiO HNCs/NF and EDLC type CNT/NF helped in holding the capacity for a long period of time. Thus, the systematic assembly of CNTs and ZnO along with the NiO decoration enlarges the application window with its high rate electrochemical properties.

Multifunctional Hierarchically Architectured ZnO for Luminescence, Photocatalytic, Electrocatalytic, and Energy Storage Applications

Hierarchically ZnO nanoarchitecture synthesized through coprecipitation technique. Growth process has been analyzed by varying pH from 5.5 to 13 along with post heat treatment process through the observation of surface morphology from 2D plates, triangular, hexagonal rods, needles, and finally to hierarchical. X-ray diffraction (XRD) reveals many intermediate phases along with ZnO which has been eliminated through the proper pH and temperature. The native defects have been discussed by using Raman and positron annihilation spectroscopy. Further, multifunctional properties of synthesized material have been discussed by candle-like warm white luminescence, photocatalysis, electrocatalysis and energy storage applications. Specially hierarchically nanoarchitecture found suitable for warm white lighting along with effective for waste water treatment by visible light. The highly porous property of the same material made itself appropriate for effective oxygen evaluation reaction and hydrogen evolution reaction together with reduced overpotential and Tafel slope. The application for supercapacitor electrode (~780 F/g) also has been revealed which opened new dimension for hierarchical ZnO.

Current Research of Graphene-Based Nanocomposites and Their Application for Supercapacitors

This review acmes the latest developments of composites of metal oxides/sulfide comprising of graphene and its analogues as electrode materials in the construction of the next generation of supercapacitors (SCs). SCs have become an indispensable device of energy-storage modes. A prompt increase in the number of scientific accomplishments in this field, including publications, patents, and device fabrication, has evidenced the immense attention they have attracted from scientific communities. These efforts have resulted in rapid advancements in the field of SCs, focusing on the development of electrode materials with features of high performance, economic viability, and robustness. It has been demonstrated that carbon-based electrode materials mixed with metal oxides and sulfoxides can perform extremely well in terms of energy density, durability, and exceptional cyclic stability. Herein, the state-of-the-art technologies relevant to the fabrication, characterization, and property assessment of graphene-based SCs are discussed in detail, especially for the composite forms when mixing with metal sulfide, metal oxides, metal foams, and nanohybrids. Effective synthetic methodologies for the nanocomposite fabrications via intercalation, coating, wrapping, and covalent interactions will be reviewed. We will first introduce some fundamental aspects of SCs, and briefly highlight the impact of graphene-based nanostructures on the basic principle of SCs, and then the recent progress in graphene-based electrodes, electrolytes, and all-solid-state SCs will be covered. The important surface properties of the metal oxides/sulfides electrode materials (nickel oxide, nickel sulfide, molybdenum oxide, ruthenium oxides, stannous oxide, nickel-cobalt sulfide manganese oxides, multiferroic materials like BaMnF, core-shell materials, etc.) will be described in each section as per requirement. Finally, we will show that composites of graphene-based electrodes are promising for the construction of the next generation of high performance, robust SCs that hold the prospects for practical applications.

Synthesis of Ni2+ ion doped ZnO–MWCNTs nanocomposites using an in situ sol–gel method: an ultra sensitive non-enzymatic uric acid sensing electrode material

Nickel (Ni²⁺) ion doped zinc oxide-multi-wall carbon nanotubes (NZC) with different composition ratios of MWCNTs (from 0.01 to 0.1 wt%) are synthesized through an in situ sol–gel method. The synthesized NZC nanocomposites (NCs) are used as electrode materials with glassy carbon electrodes (GCEs) for electrochemical detection of uric acid (UA). The cyclic voltammogram of the representative NZC 0.1 modified GCE (NZC 0.1/GCE) revealed the highest electrochemical sensing activity towards the oxidation of UA at 0.37 V in 0.2 M phosphate buffer solution (PBS) having pH 7.4 ± 0.02. The limit of detection (LOD) and limit of quantification (LOQ) for the NZC 0.1/GCE are determined to be 5.72 nM and 19.00 nM (S/N = 3) respectively, which is the lowest compared to the literature values reported for enzymatic and non-enzymatic detection techniques. The synergistic effect of NZC 0.1 NCs is proposed as one of the factors for the enhanced electrochemical oxidation of UA complemented by the phase, lattice parameters, functional groups, morphology, elemental compositions, types of bonding and specific surface area with pore size ascertained using various techniques. The synthesized NZC 0.1 NCs are further proposed as selective electrode materials for the electrochemical detection of UA as authenticated further by performing interference tests with other metabolites such as ascorbic acid (AA), dopamine (DA) and d-glucose. The optimized electrochemical studies are further adopted for sensing of UA from human excretion samples using NZC 0.1 NCs.

Nickel (Ni²⁺) ion doped zinc oxide-multi-wall carbon nanotubes (NZC) with different composition ratios of MWCNTs (from 0.01 to 0.1 wt%) are synthesized through an in situ sol–gel method.

A review on ZnO nanostructured materials: energy, environmental and biological applications

Zinc oxide (ZnO) is an adaptable material that has distinctive properties, such as high-sensitivity, large specific area, non-toxicity, good compatibility and a high isoelectric point, which favours it to be considered with a few exceptions. It is the most desirable group of nanostructure as far as both structure and properties. The unique and tuneable properties of nanostructured ZnO shows excellent stability in chemically as well as thermally stable n-type semiconducting material with wide applications such as in luminescent material, supercapacitors, battery, solar cells, photocatalysis, biosensors, biomedical and biological applications in the form of bulk crystal, thin film and pellets. The nanosized materials exhibit higher dissolution rates as well as higher solubility when compared to the bulk materials. This review significantly focused on the current improvement in ZnO-based nanomaterials/composites/doped materials for the application in the field of energy storage and conversion devices and biological applications. Special deliberation has been paid on supercapacitors, Li-ion batteries, dye-sensitized solar cells, photocatalysis, biosensors, biomedical and biological applications. Finally, the benefits of ZnO-based materials for the utilizations in the field of energy and biological sciences are moreover consistently analysed.

Current progress achieved in novel materials for supercapacitor electrodes: mini review

Supercapacitors are highly attractive for a large number of emerging mobile devices for addressing energy storage and harvesting issues. This mini review presents a summary of recent developments in supercapacitor research and technology, including all kinds of supercapacitor design techniques using various electrode materials and production methods. It also covers the current progress achieved in novel materials for supercapacitor electrodes. The latest produced EDLC/hybrid/pseudo-supercapacitors have also been described. In particular, metal oxides, specifically ZnO, used as electrode materials are in focus here. Eventually, future developments, prospects, and challenges in supercapacitor research have been elaborated on.

Fly-ash-incorporated electrospun zinc oxide nanofibers: Potential material for environmental remediation

Fly ash (FA), a solid waste generated in thermal power plants, is considered an environmental pollutant. Therefore, measures must be taken to dispose of FA in an environmentally friendly manner. In this paper, an electrospinning technique was employed to incorporate FA particles onto zinc oxide nanofibers (ZnO NFs), and the product (FA/ZnO composite) was used for the removal of methylene blue (MB) from the water. Herein, ZnO NFs may serve as effective semiconductor photocatalysts and provide sufficient surface area for FA, while the FA particles serve as an effective adsorbent. The adsorption capacity and photocatalytic efficiency of the as-synthesized nanocomposite fibers were enhanced compared to those of the pristine ZnO NFs, and this result is attributed to the uniform distribution of FA on the surface of the ZnO NFs. The as-synthesized nanocomposite could have great significance in wastewater treatment.

Production, characterization and effectiveness of cellulose acetate functionalized ZnO nanocomposite adsorbent for the removal of Se (VI) ions from aqueous media

In this study, ZnO functionalized cellulose acetate nanocomposite (ZnO/CA NC) was synthesized using a simple chemical approach found to have a high surface area of 657.34 m²/g and utilized as adsorbents for the removal of Se (VI) from aqueous solutions. Investigations on X-ray diffraction (XRD) revealed that ZnO nanocomposite has a smaller crystallite size compared to ZnO nanoparticles which facilitated for reduced agglomeration confirmed by scanning electron microscopy (SEM). The ensuing properties of ZnO/CA NC displayed high maximum adsorption capacity of 160.5 mg/g for Se (VI) ions. Inner-sphere surface complexes on ZnO/CA NC under prevailing conditions for Se (VI) were discussed using FTIR spectroscopical results. In order to evaluate the removal efficiency, the effects of adsorbent dosage, pH, and temperature were thoroughly investigated. The amount of Se (VI) ions adsorbed on ZnO/CA NC was also determined by zeta potential. The fractional removal of pollutants (Se (VI)) was done using mass transfer model. In addition, prominent adsorption capacity was also tested utilizing concurrent anions (SO₄^2-, Cl^-, and F^-) with reference to Se (VI) and cost prudent regenerability of adsorbent by NaOH solution was ascertained with anti-interference and recovery steps. ZnO/CA NC was obtained by simple chemical methodology and high surface adsorption capacities supply an encouraging technique for Se (VI) removal in water treatment applications.

Effect of Time on a Hierarchical Corn Skeleton-Like Composite of CoO@ZnO as Capacitive Electrode Material for High Specific Performance Supercapacitors

CoO–ZnO-based composites have attracted considerable attention for the development of energy storage devices because of their multifunctional characterization and ease of integration with existing components. This paper reports the synthesis of CoO@ZnO (CZ) nanostructures on Ni foam by the chemical bath deposition (CBD) method for facile and eco-friendly supercapacitor applications. The formation of a CoO@ZnO electrode functioned with cobalt, zinc, nickel and oxygen groups was confirmed by X-ray diffraction (XRD) analysis, X-ray photoelectron spectroscopy (XPS), low and high-resolution scanning electron microscopy (SEM), and transmission electron microscopy (TEM) analysis. The as-synthesized hierarchical nanocorn skeleton-like structure of a CoO@ZnO-3h (CZ3h) electrode delivered a higher specific capacitance (Cs) of 1136 F/g at 3 A/g with outstanding cycling performance, showing 98.3% capacitance retention over 3000 cycles in an aqueous 2 M KOH electrolyte solution. This retention was significantly better than that of other prepared electrodes, such as CoO, ZnO, CoO@ZnO-1h (CZ1h), and CoO@ZnO-7h (CZ7h) (274 F/g, 383 F/g, 240 F/g and 537 F/g). This outstanding performance was attributed to the excellent surface morphology of CZ3h, which is responsible for the rapid electron/ion transfer between the electrolyte and the electrode surface area. The enhanced features of the CZ3h electrode highlight potential applications in high performance supercapacitors, solar cells, photocatalysis, and electrocatalysis.

Preparation and electrochemical performance of NiCo2O4@NiCo2O4 composite nanoplates for high performance supercapacitor applications

Currently, enormous attention is being paid to the difficult design and synthesis of hierarchical nanosheet structures for high-performance supercapacitors.

Graphene and activated carbon-wrapped and Co3O4-intercalated 3D sandwich nanostructure hybrid for high-performance supercapacitance

The graphene/Co₃O₄/activated carbon (GCA) 1 : 9 capacitor shows the best electrochemical properties with Co₃O₄ particles that were homogeneously dispersed between the graphene/Co₃O₄ (GC) layers.

ZnO Nanomembrane/Expanded Graphite Composite Synthesized by Atomic Layer Deposition as Binder-Free Anode for Lithium Ion Batteries

A zinc oxide (ZnO)/expanded graphite (EG) composite was successfully synthesized by using atomic layer deposition with dimethyl zinc as the zinc source and deionized water as the oxidant source. In the composite structure, EG provides a conductive channel and mechanical support to ZnO nanomembranes, which effectively avoids the electrode pulverization caused by the volume change of ZnO. The anodes made from the flexible composite films without using binder, conductive agent, and current collector show high stable capacities especially for that with a moderate ZnO concentration. The highest capacity stayed at 438 mAh g^-1 at a current rate of 200 mA g^-1 after 500 cycles. The good performance is considered to be due to the co-effects of the high capacity of ZnO and the support of the EG framework. Such composite structures may have great potential in low-cost and flexible batteries.