Hierarchical Mesoporous 3D Flower-like CuCo2O4/NF for High-Performance Electrochemical Energy Storage

Green light-responsive photoelectrochemical sensing nanoplatform based on copper cobaltite nanorods for ultrasensitive detection of furazolidone antibiotic residue in food samples

In this research, the preparation of copper cobaltite (CuCo2O4) nanorods and its potential application in photoelectrochemical sensing platform towards ultrasensitive detection of furazolidone are reported. X-ray diffraction, Raman spectra, scanning electron microscopy, and UV-visible spectroscopy have been performed to confirm the formation, morphology, phase composition, and optical properties of CuCo2O4 synthesized by a microwave-assisted hydrothermal method. The electrochemical characteristic parameters were calculated via electrochemical impedance spectroscopy, cyclic voltammetry, differential pulse voltammetry, and chronoamperometry techniques in the absence and presence of laser light irradiation. The CuCo2O4-based photoelectrochemical sensing platform with laser light irradiation exhibited outstanding electrochemical performance compared to without laser light irradiation with sensitivity for furazolidone detection of 1.11 μA μM-1 cm-2 within the linear ranges of 0.25 to 200 μM, and detection limit of 0.03 μM, due to CuCo2O4 nanorods having a narrow energy gap, a low recombination ratio of electron-hole pairs, and multiple valence states (Co2+/Co3+ and Cu2+/Cu3+) structure. In addition, the proposed CuCo2O4-based photoelectrochemical sensor with light assistance showed good repeatability, anti-interfering capability, long-term stability, and real applicability in honey and milk samples.

Hybrid Pd0.1Cu0.9Co2O4 nano-flakes: a novel, efficient and reusable catalyst for the one-pot heck and Suzuki couplings with simultaneous transesterification reactions under microwave irradiation

We report the fabrication of a novel spinel-type Pd₀.₁Cu₀.₉Co₂O₄ nano-flake material designed for Mizoroki-Heck and Suzuki coupling-cum-transesterification reactions. The Pd₀.₁Cu₀.₉Co₂O₄ material was synthesized using a simple co-precipitation method, and its crystalline phase and morphology were characterized through powder XRD, UV-Vis, FESEM, and EDX studies. This material demonstrated excellent catalytic activity in Mizoroki-Heck and Suzuki cross-coupling reactions, performed in the presence of a mild base (K₂CO₃), ethanol as the solvent, and microwave irradiation under ligand-free conditions. Notably, the Heck coupling of acrylic esters proceeded concurrently with transesterification using various alcohols as solvents. The catalyst exhibited remarkable stability under reaction conditions and could be recycled and reused up to ten times while maintaining its catalytic integrity.

Electron transfer enhanced catalytic activity of nitrogen doped reduced graphene oxide supported CuCo2O4 towards the fast reduction of 4-nitrophenol in water

There has been a growing interest in the design and development of graphene based composite materials with superior performances for environmental catalytic applications. But in most of the studies the synthesis conditions require elevated temperatures and expensive working setups (high temperature furnaces, autoclaves, inert atmosphere conditions etc.). In this reported work, the nitrogen doped reduced graphene oxide supported CuCo2O4 (NG/CuCo2O4) composites were prepared through a simple one pot synthesis method under mild conditions (∼95 °C and air atmosphere) and successfully employed as catalysts for the reduction of toxic 4-nitrophenol (4NP). The characterization results revealed the successful formation of NG/CuCo2O4 composites with a possible charge transfer interaction between nitrogen doped reduced graphene oxide support of CuCo2O4. The NG/CuCo2O4 hybrids exhibited robust catalytic activity in 4NP reduction with an activity factor of 261.5 min-1 g-1. A 4NP conversion percentage which is as high as 99.5% was achieved within 11 min using the NG/CuCo2O4 catalyst. The detailed kinetic analysis confirmed the Langmuir-Hinshelwood model for the NG/CuCo2O4 catalysed 4NP reduction. The nitrogen doped reduced graphene oxide support modified the electronic levels of CuCo2O4 nanoparticles through electron transfer interactions and enhanced the catalytic activity of CuCo2O4 in NG/CuCo2O4 through improved adsorption of reactant ions and effective generation of active hydrogen species. The good reusability and stability along with profound activity of NG/CuCo2O4 catalyst makes it a promising material for wide scale catalytic applications.

Enhanced Catalytic Soot Oxidation over Co-Based Metal Oxides: Effects of Transition Metal Doping

A series of Co-M (M = Fe, Cr, and Mn) catalysts were synthesized by the sol-gel method for soot oxidation in a loose contact mode. The Co-Fe catalyst exhibited the best catalytic activity among the tested samples, with the characteristic temperatures (T10, T50, and T90) of 470 °C, 557 °C, and 602 °C, respectively, which were 57 °C, 51 °C, and 51 °C lower than those of the CoOx catalyst. Catalyst characterizations of N2 adsorption-desorption, X-ray diffraction (XRD), X-ray photo-electron spectrometry (XPS), and the temperature programmed desorption of O2 (O2-TPD) were performed to gain insights into the relationships between the activity of catalytic soot oxidation and the catalyst properties. The content of Co2+ (68.6%) increased due to the interactions between Co and Fe, while the redox properties and the relative concentration of surface oxygen adsorption (51.7%) were all improved, which could significantly boost the activity of catalytic soot oxidation. The effects of NO and contact mode on soot oxidation were investigated over the Co-Fe catalyst. The addition of 1000 ppm of NO led to significant reductions in T10, T50, and T90 by 92 °C, 106 °C, and 104 °C, respectively, compared to the case without the NO addition. In the tight contact mode, the soot oxidation was accelerated over the Co-Fe catalyst, resulting in 46 °C, 50 °C, and 50 °C reductions in T10, T50, and T90 compared to the loose contact mode. The comparison between real soot and model Printex-U showed that the T50 value of real soot (455 °C) was 102 °C lower than the model Printex-U soot.

Bifunctional vanadium doped mesoporous Co3O4 on nickel foam towards highly efficient overall urea and water splitting in the alkaline electrolyte

Developing more active and stable electrode materials for oxygen evolution reaction (OER) and urea oxidation reaction (UOR) is necessary for electrocatalytic water and urea oxidation which can be used to generate hydrogen. Here, a low-cost vanadium-doped mesoporous cobalt oxide on Ni foam (V/meso-Co/NF) electrodes are obtained via the grouping of an in-situ citric acid (CA)-assisted evaporation-induced self-assembly (EISA) method and electrophoretic deposition process, and work as highly efficient and long-lasting electrocatalytic materials for OER/UOR. In particular, V/meso-Co/NF electrodes require 329 mV overpotential to maintain a 50 mA/cm2, with exceptional long-term durability of 30 h. Interestingly, V/meso-Co/NF also exhibits excellent electrocatalytic UOR performance, reaching 50 and 100 mA/cm2 versus RHE at low potentials of 1.34 and 1.35 V, respectively. By employing the V/meso-Co/NF materials as both the anode and cathode, this urea electrolysis assembly V/meso-Co/NF-5 (+,-) reaches current densities of 100 mA cm-2 at 1.62 V in KOH/urea, which is nearly 340 mV lesser than classical water electrolysis. The V/meso-Co/NF-5 electrocatalysts also exhibit remarkable durability for electrocatalytic OERs and UORs. The obtained findings revealed that the synthesized V/meso-Co/NF might be a promising electrode materials for overall urea-rich wastewater management and H2 generation from wastewater.

Exchanging Anion in CuCo-Carbonate Double Hydroxide for Faradaic Supercapacitors: A Case Study

A systematic synthetic method involving the anion exchange process was designed and developed to fabricate the superior functioning three-dimensional (3-D) urchin-architectured copper cobalt oxide (CuCo₂O₄; CCO) and copper cobalt sulfide (CuCo₂S₄; CCS) electrode materials from copper-cobalt carbonate double hydroxide [(CuCo)₂(CO₃)(OH)₂; CCH]. The effective tuning of chemical, crystalline, and morphological properties was achieved during the derivatization process of CCH, based on the anion exchange effect and phase transformation without altering the 3-D spatial assembly. Benefiting from morphological and structural advantages, CCO and CCS exhibited superior electrochemical activity with capacity values of 1508 and 2502 C g^-1 at 10 A g^-1 to CCH (1182 C g^-1 at 10 A g^-1). The thermal treatment of CCH has generated a highly porous nature in nanospikes of 3-D urchin CCO structures, which purveys betterment in electrochemical phenomena than pristine smooth-surfaced CCH. Meanwhile, the sulfurization reaction induced the anion effect to a greater extent in the CCS morphology, resulting in hierarchical 3-D urchins formed by 1-D nanospikes constituting coaxially swirled 2-D nanosheets with high exposure of active sites, specific surface areas, and 3-D electron/ion transportation channels. The asymmetric supercapacitor was constructed with a superior CCS electrode as a cathode and an activated carbon electrode as an anode, showing a high specific capacity of 287.35 C g^-1 at 7 A g^-1 and durability for 5000 cycles with 94.2% retention at a high current density of 30 A g^-1. The ultrahigh energy and power density of 135.3 W h kg^-1 (10 A g^-1) and 44.35 kW kg^-1 (30 A g^-1) were harvested during the PC device performance. Our finding proposes an idea about the importance of anions and phase transformation as a versatile tool for engineering high-functioning electrode materials and their endeavor toward overwhelming the major demerit of SCs by aggrandizing the energy density value and rate performance.

Self assembled three dimensional β-Cu2V2O7 hierarchical flower decorated porous carbon: An efficient electrocatalyst for flutamide detection in biological and environmental samples

The serious situation mandates the use of anticancer drugs, which protect people all over the world from the growth of prostate cancer. In particular, excessive dosage and erroneous discharge of flutamide concentration cause make environmental pollution on the surface of the wastewater. In this study, the highly sensitive and selective electrochemical approach based on copper vanadium oxide decorated porous carbon (denoted as β-Cu₂V₂O₇/PC) composite modified glassy carbon electrode (GCE) has been developed and it was applied for sensitive detection of anticancer drug flutamide (FTM). Moreover, using the co-precipitation method, the flower-like β-Cu₂V₂O₇ hierarchical microstructure was synthesized, and through the wet chemical process, the β-Cu₂V₂O₇/PC composite was obtained. The resultant product was characterized by XRD, FTIR, RAMAN, XPS and structural morphology established by FESEM analysis. Besides that, the electrochemical characterization and properties were analyzed by cyclic voltammetry (CV) and amperometric (i-t) techniques. The β-Cu₂V₂O₇/PC/RDGCE had two linear ranges at 0.01-2.11 μM and 2.31-30.81 μM. The lower limits of detection and sensitivity were found at 0.62 nM (S/N = 3), and 24.33 μA μM^-1 cm^-2 respectively. The practicability test was applied for the determination of FTM in urine, blood serum and environmental aquatic fluid with satisfactory recovery obtained.

Magnesium-Modified Co3O4 Catalyst with Remarkable Performance for Toluene Low Temperature Deep Oxidation

Co3O4, MgCo2O4 and MgO materials have been synthesized using a simple co-precipitation approach and systematically characterized. The total conversion of toluene to CO2 and H2O over spinel MgCo2O4 with wormlike morphology has been investigated. Compared with single metal oxides (Co3O4 and MgO), MgCo2O4 with the highest activity has exhibited almost 100% oxidation of toluene at 255 °C. The obtained results are analogous to typical precious metal supported catalysts. The activation energy of toluene over MgCo2O4 (38.5 kJ/mol) is found to be much lower than that of Co3O4 (68.9 kJ/mol) and MgO ((87.8 kJ/mol)). Compared with the single Co and Mg metal oxide, the as-prepared spinel MgCo2O4 exhibits a larger surface area, highest absorbed oxygen and more oxygen vacancies, thus highest mobility of oxygen species due to its good redox capability. Furthermore, the samples specific surface area, low-temperature reducibility and surface adsorbed oxygenated species ratio decreased as follows: MgCo2O4 > Co3O4 > MgO; which is completely in line with the catalytic performance trends and constitute the reasons for MgCo2O4 high excellent activity towards toluene total oxidation. The overall finding supported by ab initio molecular dynamics simulations of toluene oxidation on the Co3O4 and MgCo2O4 suggest that the catalytic process follows a Mars–van Krevelen mechanism.

Electrochemically active site-rich nanocomposites of two-dimensional materials as anode catalysts for direct oxidation fuel cells: new age beyond graphene

Direct oxidation fuel cell (DOFC) has been opted as a green alternative to fossil fuels and intermittent energy resources as it is economically viable, possesses good conversion efficiency, as well as exhibits high power density and superfast charging. The anode catalyst is a vital component of DOFC, which improves the oxidation of fuels; however, the development of an efficient anode catalyst is still a challenge. In this regard, 2D materials have attracted attention as DOFC anode catalysts due to their fascinating electrochemical properties such as excellent mechanical properties, large surface area, superior electron transfer, presence of active sites, and tunable electronic states. This timely review encapsulates in detail different types of fuel cells, their mechanisms, and contemporary challenges; focuses on the anode catalyst/support based on new generation 2D materials, namely, 2D transition metal carbide/nitride or carbonitride (MXene), graphitic carbon nitride, transition metal dichalcogenides, and transition metal oxides; as well as their properties and role in DOFC along with the mechanisms involved.

Metal Oxide-Related Dendritic Structures: Self-Assembly and Applications for Sensor, Catalysis, Energy Conversion and Beyond

In the past two decades, we have learned a great deal about self-assembly of dendritic metal oxide structures, partially inspired by the nanostructures mimicking the aesthetic hierarchical structures of ferns and corals. The self-assembly process involves either anisotropic polycondensation or molecular recognition mechanisms. The major driving force for research in this field is due to the wide variety of applications in addition to the unique structures and properties of these dendritic nanostructures. Our purpose of this minireview is twofold: (1) to showcase what we have learned so far about how the self-assembly process occurs; and (2) to encourage people to use this type of material for drug delivery, renewable energy conversion and storage, biomaterials, and electronic noses.

Synthesis, Characterization and Applications of Spinel Cobaltite Nanomaterials

Recently, spinel structures (AB₂O₄) Nanoparticles (NPs) having binary and ternary mixtures of metal oxides have been established as promising redox catalysts. Due to the presence of two mixed valence metal cations, transport of electrons takes place easily between multiple transition-metal cations with relatively low energy of activation. Among these, spinel cobaltite (MCo₂O₄) is very attractive due to its low cost, non-toxicity, higher stability, higher electronic conductivity and electrochemical property. To date, MCo₂O₄ has been used in the fabrication of supercapacitors, electrodes for oxygen evolution reaction, and electrochemical sensors for glucose. A variety of MMCo₂O₄materials have been synthesized, characterized, and utilized in the fabrication of super capacitors, electrodes for oxygen evolution reaction, and electrochemical sensors for glucose. The progress in the field of the spinel MCo₂O₄ materials opens the door to novel and efficient applications in the nanoscience and nanotechnology, and elctrochemistry.

Surface chemical functionality of carbon dots: influence on the structure and energy storage performance of the layered double hydroxide

As a kind of zero-dimensional material, carbon dots (CDs) have become a kind of promising novel material due to their incomparable unique physical and chemical properties. Despite the optical properties of CDs being widely studied, their surface chemical functions are rarely reported. Here we propose an interesting insight into the important role of surface chemical properties of CDs in adjusting the structure of the layered double hydroxide (LDH) and its energy storage performance. It was demonstrated that CDs with positive charge (p-CDs) not only reduce the size of the flower-like LDH through affecting the growth of LDH sheets, but also act as a structure stabilizer. After calcination, the layered double oxide (LDO) maintained the morphology of the LDH and prevented the stacking of layers. And the superiority of the composite in lithium-ion batteries (LIBs) was demonstrated. When used as an anode of LIBs, composites possess outstanding specific capacity, cycle stability and rate performance. It presents the discharge capacity of 1182 mA h g-1 and capacity retention of 94% at the current density of 100 mA g-1 after 100 cycles. Our work demonstrates the important chemical functions of CDs and expands their future applications.

Enhanced Supercapacitive Performance of Higher-Ordered 3D-Hierarchical Structures of Hydrothermally Obtained ZnCo2O4 for Energy Storage Devices

The demand for eco-friendly renewable energy resources as energy storage and management devices is increased due to their high-power density and fast charge/discharge capacity. Recently, supercapacitors have fascinated due to their fast charge-discharge capability and high-power density along with safety. Herein, the authors present the synthesis of 3D-hierarchical peony-like ZnCo2O4 structures with 2D-nanoflakes by a hydrothermal method using polyvinylpyrrolidone. The reaction time was modified to obtain two samples (ZCO-6h and ZCO-12h) and the rest of the synthesis conditions were the same. The synthesized structures were systematically studied through various techniques: their crystalline characteristics were studied through XRD analysis, their morphologies were inspected through SEM and TEM, and the elemental distribution and oxidation states were studied by X-ray photoelectron spectroscopy (XPS). ZCO-12h sample has a larger surface area (55.40 m2·g-1) and pore size (24.69 nm) than ZCO-6h, enabling high-speed transport of ions and electrons. The ZCO-12h electrode showed a high-specific capacitance of 421.05 F·g-1 (31.52 C·g-1) at 1 A·g-1 and excellent cycle performance as measured by electrochemical analysis. Moreover, the morphologic characteristics of the prepared hierarchical materials contributed significantly to the improvement of specific capacitance. The excellent capacitive outcomes recommend the 3D-ZnCo2O4 hierarchical peony-like structures composed of 2D-nanoflakes as promising materials for supercapacitors with high-performance.

Designing of Carbon Nitride Supported ZnCo2O4 Hybrid Electrode for High-Performance Energy Storage Applications

This study reports a unique graphitic-C₃N₄ supported ZnCo₂O₄ composite, synthesized through a facile hydrothermal method to enhance the electrochemical performance of the electrode. The g-C₃N₄@ZnCo₂O₄ hybrid composite based electrode exhibits a significant increase in specific surface area and maximum specific capacity of 157 mAhg⁻¹ at 4 Ag⁻¹. Moreover, g-C₃N₄@ZnCo₂O₄ electrode maintained significant capacity retention of 90% up to 2500 cycles. Utilizing this composite in the development of the symmetric device, g-C₃N₄@ZnCo₂O₄//g-C₃N₄@ZnCo₂O₄ displays a specific capacity of 121 mAhg⁻¹. The device exhibits an energy density of 39 Whkg⁻¹ with an equivalent power density of 1478 Wkg⁻¹. A good cycling stability performance with an energy efficiency of 75% and capacity retention of 71% was observed up to 10,000 cycles. The superior performance of g-C₃N₄@ZnCo₂O₄ is attributed to the support of the g-C₃N₄ which increases the surface area, electroactive sites and provides chemical stability for electrochemical performance. The outstanding performance of this exclusive device symbolizes remarkable progress in the direction of high-performance energy storage applications.

Designing positive electrodes based on 3D hierarchical CoMn2O4@NiMn-LDH nanoarray composites for high energy and power density supercapacitors

3D hierarchical CoMn₂O₄@NiMn-LDH core–shell nanowire arrays as positive electrodes for high energy and power density supercapacitors.

Reduced graphene oxide supported quasi-two-dimensional ZnCo2O4 nanosheets for lithium ion batteries with high electrochemical stability

In this work, quasi-two-dimensional spinel ZnCo2O4 (ZCO) nanosheets comprising ZCO nanoparticles of different grain size were prepared via a facile solvothermal method and followed by post-treatment. It shows that the ZCO with a small grain size can be obtained by a fast cooling post-treatment. To enhance the conductivity of ZCO, uniform and compact ZCO nanosheets were in situ grown on reduced graphene oxide (rGO), which was employed as the template. When used as an anode for lithium ion batteries (LIBs), rGO@ZCO has a highly reversible capacity of 1107.2 mAh · g-1 at 100 mA · g-1 after 100 cycles, which is the highest among all ZCO samples. Moreover, when the current density is from 50 to 500 mA · g-1, the capacity of rGO@ZCO decreased from 1046.5 to 527.6 mAh · g-1, implying superior rate ability. The electrochemical analysis, together with calculations demonstrates that the unique structure is beneficial to promote charge transport and adapt the volume change in the charge-discharge process, resulting in expected LIB performance.

Three-dimensional mesoporous sandwich-like g-C3N4-interconnected CuCo2O4 nanowires arrays as ultrastable anode for fast lithium storage

Inspite of their impressive high theoretical capacity as Lithium-ion batteries (LIBs) anodes, spinel transition-metal oxides (TMOs) suffer serious volume expansion, aggregation and the pulverization of crystal structures during lithiation/delithiation, and this process severely restrict their industrial application. Multi-dimensional morphological engineering of spinel TMO nanostructures is an effective way to solve this issue. In this work, using facile hydrothermal synthetic methods, spinel CuCo₂O₄ nanowires arrays are synthesized and supported on g-C₃N₄ nanosheets, thus forming a unique sandwich-like interconnected three-dimensional mesoporous structure containing high amount of void spaces. Addition of g-C₃N₄ nanosheets to CuCo₂O₄ nanowire arrays may shorten the Li⁺ diffusion distance and electron transfer pathway, and may also provide more active sites for Li⁺ diffusion into electrolyte and buffer for the volume expansion and aggregation of CuCo₂O₄. As a LIB anode material, CuCo₂O₄@g-C₃N₄ shows initial lithiation capacity of 840.6 mAh g^-1, and capacity retention of 641.2 mAh g^-1 after 60 cycles at the current density of 0.1 A g^-1 and 499.2 mAh g^-1 after 40 cycles at high current of 1 A g^-1, which is significantly better than value of pure CuCo₂O₄ nanowires. This work affords a new way to tackle the problem of volume expansion of high capacity spinel TMO anode materials using g-C₃N₄ nanosheets as buffering agent.

Facile Preparation of Porous Rod-like Cu x Co3-x O4/C Composites via Bimetal-Organic Framework Derivation as Superior Anodes for Lithium-Ion Batteries

To meet growing demand of energy, lithium-ion batteries (LIBs) are under enormous attention. The development of well-designed ternary transition metal oxides with high capacity and high stability is important and challengeable for using as electrode materials for LIBs. Herein, a new and highly reversible carbon-coated Cu-Co bimetal oxide composite material (Cu x Co3-x O4/C) with a one-dimensional (1D) porous rod-like structure was prepared through a bimetal-organic framework (BMOF) template strategy followed by a morphology-inherited annealing treatment. During the annealing process, carbon derived from organic frameworks in situ fully covered the synthesized bimetal oxide nanoparticles, and a large number of porous spaces were generated in the MOF-derived final samples, thus ensuring high electrical conductivity and fast ion diffusion. Benefiting from the synergetic effect of bimetals, the unique 1D porous structure, and conductive carbon network, the as-synthesized Cu x Co3-x O4/C delivers a high capacity retention up to 92.4% after 100 cycles, with a high reversible capacity still maintained at 900 mA h g-1, indicating an excellent cycling stability. Also, a good rate performance is demonstrated. These outstanding electrochemical properties show us a concept of synthesis of MOF-derived bimetal oxides combining both advantages of carbon incorporation and porous structure for progressive lithium-ion batteries.

Hexagonal CuCo₂O₄ Nanoplatelets, a Highly Active Catalyst for the Hydrolysis of Ammonia Borane for Hydrogen Production

Catalytic hydrolysis of ammonia borane (AB) has been considered as an effective and safe method to generate hydrogen. Development of highly active and low-cost catalysts is one of the key tasks for this technology. In this work, hexagonal CuCo₂O₄ nanoplatelets with a thickness of approximately 55 nm were prepared. In AB hydrolysis, those nanoplatelets exhibited ultrahigh catalytic activity with turnover frequency (TOF) of 73.4 molhydrogen min-1 molcat-1. As far as we know, this is one of the highest TOF values ever reported for non-noble metal catalysts. In addition, the effects of viscosity and different alkalis on the hydrolysis were also investigated. It is revealed that high viscosity of the reaction medium will retard the hydrolysis reaction. The presence of NaOH, KOH, and Na₂CO₃ in the reaction solution is favorable for hydrolytic process. In contrast, NH₃·H₂O will slow down the hydrolysis rate of ammonia borane. This work can provide some novel insight into the design of catalysts with both high performance and low cost. Besides, some findings in the present study can also offer us some information about how to improve the hydrolysis rates by optimizing the hydrolysis condition.

Hydrothermally Tailored Three-Dimensional Ni-V Layered Double Hydroxide Nanosheets as High-Performance Hybrid Supercapacitor Applications

Here, we report a facile and easily scalable hydrothermal synthetic strategy to synthesize Ni-V layered double hydroxide (NiV LDH) nanosheets toward high-energy and high-power-density supercapacitor applications. NiV LDH nanosheets with varying Ni-to-V ratios were prepared. Three-dimensional curved nanosheets of Ni_0.80V_0.20 LDH showed better electrochemical performance compared to other synthesized NiV LDHs. The electrode coated with Ni_0.80V_0.20 LDH nanosheets in a three-electrode cell configuration showed excellent pseudocapacitive behavior, having a high specific capacity of 711 C g^-1 (1581 F g^-1) at a current density of 1 A g^-1 in 2 M KOH. The material showed an excellent rate capability and retained the high specific capacity of 549 C g^-1 (1220 F g^-1) at a current density of 10 A g^-1 and low internal resistances. Owing to its superior performance, Ni_0.80V_0.20 LDH nanosheets were used as positive electrode and commercial activated carbon was used as negative electrode for constructing a hybrid supercapacitor (HSC) device, having a working voltage of 1.5 V. The HSC device exhibited a high specific capacitance of 98 F g^-1 at a current density of 1 A g^-1. The HSC device showed a higher energy density of 30.6 Wh kg^-1 at a power density of 0.78 kW kg^-1 and maintained a high value of 24 Wh kg^-1 when the power density was increased to 11.1 kW kg^-1. The performance of NiV LDHs nanosheets indicates their great potential as low-cost electrode material for future energy-storage devices.

Nanosheets of CuCo2O4 As a High-Performance Electrocatalyst in Urea Oxidation

The urea oxidation reaction (UOR) is a possible solution to solve the world’s energy crisis. Fuel cells have been used in the UOR to generate hydrogen with a lower potential compared to water splitting, decreasing the costs of energy production. Urea is abundantly present in agricultural waste and in industrial and human wastewater. Besides generating hydrogen, this reaction provides a pathway to eliminate urea, which is a hazard in the environment and to people’s health. In this study, nanosheets of CuCo2O4 grown on nickel foam were synthesized as an electrocatalyst for urea oxidation to generate hydrogen as a green fuel. The synthesized electrocatalyst was characterized using X-ray diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy. The electroactivity of CuCo2O4 towards the oxidation of urea in alkaline solution was evaluated using electrochemical measurements. Nanosheets of CuCo2O4 grown on nickel foam required the potential of 1.36 V in 1 M KOH with 0.33 M urea to deliver a current density of 10 mA/cm2. The CuCo2O4 electrode was electrochemically stable for over 15 h of continuous measurements. The high catalytic activities for the hydrogen evolution reaction make the CuCo2O4 electrode a bifunctional catalyst and a promising electroactive material for hydrogen production. The two-electrode electrolyzer demanded a potential of 1.45 V, which was 260 mV less than that for the urea-free counterpart. Our study suggests that the CuCo2O4 electrode can be a promising material as an efficient UOR catalyst for fuel cells to generate hydrogen at a low cost.

Sustainable fixation of CO2 into epoxides to form cyclic carbonates using hollow marigold CuCo2O4 spinel microspheres as a robust catalyst

The present work demonstrates the chemical fixation of CO₂ for the synthesis of organic carbonates using mesoporous hollow marigold CuCo₂O₄ spinel microspheres as a catalyst prepared using the solvothermal method.

An urchin-like MgCo2O4@PPy core-shell composite grown on Ni foam for a high-performance all-solid-state asymmetric supercapacitor

In recent years, the electrochemical properties of supercapacitors have been greatly improved due to continuous improvement in their composite materials. In this study, an urchin-like MgCo2O4@PPy/NF (MgCo2O4@polypyrrole/Ni foam) core-shell structure composite material was successfully developed as an electrode for supercapacitors. The MCP-2 composite material, obtained by a hydrothermal method and in situ chemical oxidative polymerization, shows a high specific capacitance of 1079.6 F g-1 at a current density of 1 A g-1, which is much higher than that of MC (783.6 F g-1) under the same conditions. Simultaneously, it has low resistance and an excellent cycling stability of 97.4% after 1000 cycles. Furthermore, an all-solid-state asymmetric supercapacitor (ASC) was assembled using MCP-2 as the positive electrode and activated carbon (AC) as the negative electrode. The MCP-2//AC ASC exhibits high specific capacitance (94 F g-1 at a current density of 0.4 A g-1), high energy density (33.4 W h kg-1 at a power density of 320 W kg-1), high volumetric energy density (17.18 mW h cm-3 at a volumetric power density of 0.16 W cm-3) and excellent cycling stability (retaining 91% of the initial value after 10 000 cycles). Simultaneously, the device has low leakage current and excellent self-discharge characteristics. All these results indicate that the MCP-2//AC ASC is a good energy storage device; it can support the function of two LEDs for 20 minutes. These results indicate that the MCP-2//AC ASC will play an important role in energy structures in the future.

Facile and cost-effective growth of a highly efficient MgCo2O4 electrocatalyst for methanol oxidation

MgCo₂O₄ nanorods show superior electrochemical performance when used as an electrocatalyst for methanol electrooxidation.

Origin of Fracture-Resistance to Large Volume Change in Cu-Substituted Co3 O4 Electrodes

The electrode materials conducive to conversion reactions undergo large volume change in cycles which restrict their further development. It has been demonstrated that incorporation of a third element into metal oxides can improve the cycling stability while the mechanism remains unknown. Here, an in situ and ex situ electron microscopy investigation of structural evolutions of Cu-substituted Co₃ O₄ supplemented by first-principles calculations is reported to reveal the mechanism. An interconnected framework of ultrathin metallic copper formed provides a high conductivity backbone and cohesive support to accommodate the volume change and has a cube-on-cube orientation relationship with Li₂ O. In charge, a portion of Cu metal is oxidized to CuO, which maintains a cube-on-cube orientation relationship with Cu. The Co metal and oxides remain as nanoclusters (less than 5 nm) thus active in subsequent cycles. This adaptive architecture accommodates the formation of Li₂ O in the discharge cycle and underpins the catalytic activity of Li₂ O decomposition in the charge cycle.

Enhanced Fenton-like catalytic performance of N-doped graphene quantum dot incorporated CuCo2O4

In the present study, a novel nanocomposite based on CuCo₂O₄ and N-doped graphene quantum dots (N-GQDs) as an iron-free heterogeneous Fenton-like catalyst was prepared by a two-step solvothermal method.

Designed fabrication of three-dimensional δ-MnO2-cladded CuCo2O4 composites as an outstanding supercapacitor electrode material

Three-dimensional δ-MnO₂-cladded CuCo₂O₄ composites on Ni foam have been designed via a hydrothermal method followed by one-pot chelation-mediated aqueous processes.

P–p heterojunction CuO/CuCo2O4 nanotubes synthesized via electrospinning technology for detecting n-propanol gas at room temperature

Composite CuO/CuCo₂O₄ nanotubes were synthesized by electrospinning technology. The large specific surface area, complex tubular structure, and p–p heterojunction are the potential reasons for the excellent room temperature gas sensing performance toward n-propanol vapor.

Free standing growth of MnCo2O4 nanoflakes as an electrocatalyst for methanol electro-oxidation

A binder and carbon-free electrodeposited MnCo₂O₄/NF electrode displays superior electrochemical performance and stability for the application of methanol oxidation.