ZnCo2O4 Research Articles

Understanding the Enhanced Capacitive Desalination Performance of Spherical ZnCo2O4 Electrode

AbstractIn this work, the spinel ZnCo2O4 (ZCO) prepared by a simple strategy is employed for capacitive deionization (CDI) towards enhanced desalination performance. The ZCO reveals typical spherical structure that is beneficial in providing 3D tunnels for ions diffusion. On the basis of electrochemical measurements, the ZCO electrode possesses specific capacitance of 307.9 F g−1 in 1 m NaCl solution at the scan rate of 1 mV s−1. Remarkably, the equivalent series resistance and the Warburg impedance of ZCO electrode is only 0.54 and 0.66 Ω, respectively. Such low resistivity is conducive to improve the efficiency of charge transfer and the driven energy utilization. Regarding the desalination, the ZCO electrode illuminates the salt removal capacity of 39.4 mg g−1 in 2000 µS cm−1 NaCl solution at 1.2 V. Under the same experimental conditions, the ZCO electrode demonstrates a high desalination capacity of 73.39 mg g−1 with charge efficiency of 76.8% at a constant current of 10 mA g−1. Moreover, the preferential removal of Na+, K+, and Mg2+ enabled by ZCO electrode is investigated, suggesting the radius of hydration ions plays a significant role. Beyond that, the analysis on the morphology, crystal phase, and valance state of ZCO electrode at different desalination/salination state are explored to propose the possible desalination mechanism.

All‐Amorphous Junction Field‐Effect Transistors Based on High‐Mobility Zinc Oxynitride

AbstractThis report is on the electrical properties of all‐amorphous junction field‐effect transistors (JFETs) based on n‐type zinc oxynitride (ZnON) as a channel material and room‐temperature deposited p‐type ZnCo2O4 (ZCO) as a heterojunction gate. Devices with different channel thicknesses are thereby compared. Best devices with 48 nm channel layer thickness achieve drain current on/off–ratios of 105 and low subthreshold swing of 134 mV dec−1 within a gate voltage sweep of less than 2 V. The channel mobility extraction is reliable for 90 nm‐thick channels yielding saturation mobility values over 50 cm2 V−1 s−1. For JFETs with 48 nm‐thick channels an overestimation of the saturation mobility due to deviations from the ideal transistor characteristics is determined.

Enhanced visible-light utilization with ZnCo2O4–BiErWO6 heterojunctions towards photocatalytic degradation of antibiotics

Herein, zinc cobaltite–bismuth erbium tungstate (ZC–BE) nanocomposites have been successfully synthesized by a simple hydrothermal method. The hybrid ZC–BE nanocomposites was carefully investigated using field emission scanning electron microscopy (FE-SEM), high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), diffuse reflectance spectroscopic measurements (DRS), Raman, and electrochemical impedance studies (EIS) respectively. The photocatalytic degradation of model pollutant ciprofloxin (CIP) was evaluated using the as-prepared ZC–BE samples upon visible-light irradiation. The photocatalytic degradation efficiency of the nanocomposite with 15 wt% ZC composition displayed an excellent degradation rate of CIP of 91.24% within 120 min which was higher than that of pure ZnCo2O4 (ZC) and BiErWO6 (BE) alone. Such an improvement was primarily credited to the construction of a suitable heterojunction between BE and ZC, superior visible-light absorption and sluggish recombination of photogenerated electron–holes in the photocatalyst process. Based on the experimental results, a plausible degradation mechanism for the CIP under the visible light was discussed. Hence, ZC–BE heterostructure may be a promising visible-light-responsive photocatalyst for removing pharmaceutical pollutants in wastewater.

In situ engineered 0D interconnected network-like CNS decorated on Co-rich ZnCo2O4 2D nanosheets for high-performance supercapacitors

Co-rich ZnCo2O4 (ZCO) two-dimensional (2D) nanosheets are decorated with highly porous, glucose-derived, zero-dimensional (0D) interconnected network-like carbon nanospheres (CNS) using an in situ hydrothermal method. The content of CNS in the reaction is varied to produce two different composites (CNS@ZCO-I and CNS@ZCO-II). Their physicochemical properties are examined and compared with those of the pristine-CNS and ZCO samples. The non-stoichiometry of the elements in ZCO of the composites is quantified by X-ray diffraction using a Reitveld refinement and X-ray photoelectron spectroscopy. CNS@ZCO-II is found to be Co-rich in ZnCo2O4 compared to the other samples. The high surface area of the CNS and non-stoichiometry of Zn/Co in the composites provide a short ion/electron transport path distance, high electronic conductivity, additional electrochemical active sites, and stable structural integrity. This viable strategy offers a good interaction between the CNS and ZCO, which translates to better electrochemical activity as an electrode material for energy storage devices. The CNS@ZCO-II composite with a higher CNS concentration shows an excellent electrochemical performance of approximately 1116.24 F g−1 at 0.35 A g−1 (compared to the pristine-ZCO and CNS@ZCO-I composite).

Efficient Laser-Induced Construction of Oxygen-Vacancy Abundant Nano-ZnCo2 O4 /Porous Reduced Graphene Oxide Hybrids toward Exceptional Capacitive Lithium Storage.

Recently, binary ZnCo2 O4 has drawn enormous attention for lithium-ion batteries (LIBs) as attractive anode owing to its large theoretical capacity and good environmental benignity. However, the modest electrical conductivity and serious volumetric effect/particle agglomeration over cycling hinder its extensive applications. To address the concerns, herein, a rapid laser-irradiation methodology is firstly devised toward efficient synthesis of oxygen-vacancy abundant nano-ZnCo2 O4 /porous reduced graphene oxide (rGO) hybrids as anodes for LIBs. The synergistic contributions from nano-dimensional ZnCo2 O4 with rich oxygen vacancies and flexible rGO guarantee abundant active sites, fast electron/ion transport, and robust structural stability, and inhibit the agglomeration of nanoscale ZnCo2 O4 , favoring for superb electrochemical lithium-storage performance. More encouragingly, the optimal L-ZCO@rGO-30 anode exhibits a large reversible capacity of ≈1053 mAh g-1 at 0.05 A g-1 , excellent cycling stability (≈746 mAh g-1 at 1.0 A g-1 after 250 cycles), and preeminent rate capability (≈686 mAh g-1 at 3.2 A g-1 ). Further kinetic analysis corroborates that the capacitive-controlled process dominates the involved electrochemical reactions of hybrid anodes. More significantly, this rational design holds the promise of being extended for smart fabrication of other oxygen-vacancy abundant metal oxide/porous rGO hybrids toward advanced LIBs and beyond.

Temperature-dependent transport properties of micro and nano-sized zinc cobalt oxide (ZnCo2O4) and zinc manganese oxide (ZnMn2O4) particles synthesized by a hydrothermal route

In the present work, a hydrothermal method has been adopted to synthesize micro (~150 nm), and nano (~20 nm) particles of Zinc based, cobalt, and manganese oxide structures, i.e., ZnCo2O4 (ZCO) and ZnMn2O4 (ZMO). These structures have been examined by X-ray diffraction, Field-emission scanning electron microscopy with energy-dispersive X-ray spectroscopy, transmission electron microscopy, and Fourier transform infrared spectroscopy. The effect of different reducing agents and solvents have been ascertained on the morphological and the crystalline nature of the samples. The highly crystalline and micron-sized particle formation has been observed with the usage of NaBH4 as the reductant in the water solution, and a polycrystalline structure with nanosized particle formation has been found with NaOH as the reductant in the water and DMF solution. The electrical properties have been investigated between 100 Hz and 1 MHz by varying the temperature from 303 K to 513 K. The micro and nano sized particles of ZCO and ZMO have shown frequency dependence, thermally activated and relaxation-type dielectric behavior confirming the semiconducting nature. The variation of ac conductivity with frequency at different temperatures is according to Jonscher's power law for micro and nano sized particles of the ZCO and ZMO but supporting different conduction mechanisms. The conduction mechanism in microparticles and nano-particles is according to an overlapping-large polaron tunneling (OLPT) model, and the Non-overlapping small polaron tunneling (NSPT) model, respectively.

Mesoporous ZnCo2O4-CNT microflowers as bifunctional material for supercapacitive and lithium energy storage

As one kind of binary transition metal oxide, ZnCo2O4 (ZCO) displays excellent specific capacitance/capacity and high energy density as electrodes of supercapacitors (SCs) and lithium ion battery (LIBs). Introducing carbon materials has become a common method to obtain higher performance. In this work, the electronic property of ZnCo2O4 was firstly studied by Density Functional Theory to provide a theoretical support for the ZnCo2O4-CNT (ZCO-CNT) composite as electrode materials. Then, the composite was synthesized in a facile one-step hydrothermal way. The homogenous combination of the ZnCo2O4 microflower with CNTs provided continuous electron transmission channels and fast electron transfer inside the composite, which also absorbed the stress in electrochemical reactions, and therefore helped maintaining a stable composite structure during cycling. Besides, the microscale dimension of ZCO-CNT flowers can also alleviate self-aggregation and stable structure during electrochemical reactions. As the positive electrode of asymmetric supercapacitor, the ZCO-CNT//activated carbon device demonstrated an energy density of 24.46 Wh·kg−1 at a power density of 750 W·kg−1, as well as a high capacitance retention of 84.6% after 3000 cycles. Furthermore, as for LIBs, ZCO-CNT was regarded as a kind of potential anode electrode material. An excellent reversible capacity of 1200 mAh·g−1 could be obtained after 120 cycles at 200 mA·g−1.

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.

Aqueous asymmetric supercapacitors based on ZnCo2O4 nanoparticles via facile combustion method

ZnCo2O4 (ZCO) nanoparticles are synthesized via a facile, fast and cost-effective combustion method. The effect of calcination temperature is studied on the morphology, crystallite size and electrochemical properties of the ZCO. Scanning electron microscope observation reveals that the calcination temperature strongly influences the morphology of the prepared ZCO. At the calcination temperatures of 300, 400 and 600 °C, the ZCO samples show the specific capacitance values of 202, 668 and 843 F g−1, respectively with the current density of 1 A g−1. Furthermore, higher calcination temperature (800 °C) leads to rapid increment of particle size, low specific capacitance (432 F g−1 at 1 A g−1) and inferior rate capability of ZCO, which may be related to the severe micro-strain and crack formation upon repeated electrolytic ions during charging-discharging process. Owing to the excellent specific capacitance of the ZCO (prepared at 600 °C), its performance is further investigated in asymmetric supercapacitor (ASC) device and a high energy density of 26.28 W h kg−1 is obtained at the power density of 716 W kg−1 under the current density of 1 A g−1. Parallel-connected 14 light-emitting diodes are lit up from series-connected two ASCs. In addition, a motor fan is powered by the two ASCs. In the light of the above results, the ZCO nanoparticles may be expected to be a prospective viable electrode material for high-performance supercapacitors.

Rapid and Low-Temperature Salt-Templated Production of 2D Metal Oxide/Oxychloride/Hydroxide.

2D materials have played an important role in electronics, sensors, optics, electrocatalysis, and energy storage. Many methods for the preparation of 2D materials have been explored. It is crucial to develop a high-yield, rapid, and low-temperature method to synthesize 2D materials. A general, fast (5 min), and low-temperature (≈100 °C) salt (CoCl2 ·6H2 O)-templated method is proposed to prepare series of 2D metal oxides/oxychlorides/hydroxides in large scale, such as MoO3 , SnO2 , SiO2 , BiOCl, Sb4 O5 Cl2 , Zn2 Co3 (OH)10 2H2 O, and ZnCo2 O4 . The as-synthesized 2D materials possess an ultrathin feature (2-7 nm) and large aspect ratios. Additionally, these 2D metal oxides/oxychlorides/hydroxides exhibit good electrochemical properties in energy storage (lithium/sodium-ion batteries) and electrocatalysis (hydrogen/oxygen evolution reaction).

Microwave synthesis: ZnCo2O4 NPs as an efficient electrocatalyst in the methanol oxidation reaction

Herein, we report the electrocatalytic activity of ZnCo2O4 (ZCo) NPs in the methanol oxidation reaction. Cubic shaped ZCo NPs were grown directly on nickel foam (NF) using a microwave-assisted synthesis method with heating at 180 °C for 15 min. The Ipc value for ZnCo2O4 NPs at 0.7 V was 222.3 mA cm−2. Cyclic voltammetry (CV) indicated that ZnCo2O4 NPs enhance the methanol oxidation reaction.

Synthesis and theoretical calculations of N-doped ZnCo2O4 anode for lithium-ion anode via gradient pressure-induced processes and theoretical calculations

The aim of this study is to improve the electrochemical performance of ZnCo2O4 (ZCO) anode by two-steps nitrogen doping processes, including hydrothermal reaction process and atmospheric pressure plasma jet process (APPJ). Via the higher-pressure hydrothermal method, nitrogen was doped in the ZCO spinel lattice, while subsequently “atmospheric-pressure” APPJ mainly activated and modified the electrode surface binding with the dangling bond. The uniformity, chemical composition, and crystal structure of ZCO and N-ZCO were examined by electron probe microanalyzer (EPMA), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). First principle calculation based on density functional theory (DFT) results clearly reveal that N-doping could significantly narrow band gap and enhance the electronic transfer towards ZCO framework. Nitrogen doping effectively improves electrochemical performance with superior capacity (1025 mAh⋅g−1) and stability with 63% cycling retention after 100 cycles at a current density of 1C. This study provides a rapid and inexpensive nitrogen doping processes to efficiently promote the ZCO electrochemical performance for anode materials.

Low-Cost Rapid Template-Free Synthesis of Nanoscale Zinc Spinels for Energy Storage and Electrocatalytic Applications

Spinels form an interesting class of compounds, finding applications in metal-ion batteries and as catalysts for metal–air batteries and fuel cells. Here, we report a fast, template-free solution combustion method to synthesize nanoscale zinc spinels for applications as cathodes in low-cost aqueous zinc-ion batteries and oxygen reduction reaction (ORR) catalysts. It leads to the formation of phase-pure spinels with near spherical nanoscale morphology. Three spinels—ZnCo2O4 (ZCO), ZnMn2O4 (ZMO), and ZnMnCoO4 (ZMCO)—were investigated. ZMO and, for the first time, ZMCO were observed to show reversible Zn (de)insertion involving Mn4+/Mn3+ redox couple with a first discharge capacity of 109.4 mAh/g (i.e., >99% of theoretical capacity). Further, these Zn-based spinels showed appreciable oxygen reduction reaction (ORR) electrocatalytic activity. The ORR activity in alkaline solution was characterized by cyclic voltammetry (CV) and linear sweep voltammetry (LSV) using a rotating disk electrode (RDE) and was obser...

Promotive Effect of MWCNT on ZnCo2O4 Hexagonal Plates and Their Application in Aqueous Asymmetric Supercapacitor

ZnCo2O4 (ZCO) hexagonal nanoplates were synthesized by a facile, robust and cost-effective co-precipitation method. The as-synthesized nanoplates were utilized as an electrode material and their electrochemical properties were investigated in three-electrode and two-electrode configurations with aqueous electrolyte of 1 M KOH. The fabricated ZCO electrode materials exhibited a specific capacity of 37 mAh g−1 at 1 A g−1. The capacity of the pristine ZCO nanoplates was further improved by incorporating multiwall carbon nanotubes (MWCNTs). The MWCNT@ZCO showed a specific capacity of 64 mAh g−1 at 1 A g−1. To examine practical performances, asymmetric supercapacitor (ASC) was also fabricated using MWCNT@ZCO as a positive electrode and activated carbon as a negative electrode. The specific capacity of the ASC was found to be 17 mAh g−1 at 0.38 A g−1. ASC could store sufficient energy to power a parallel combination of two red color light-emitting diodes. These findings may open new opportunities for the design of effective, stable, and easily recyclable ZCO electrode material for energy storage devices.

Metal-Organic Framework Templated 3D Hierarchical ZnCo2 O4 @Ni(OH)2 Core-Shell Nanosheet Arrays for High-Performance Supercapacitors.

Designing core-shell electrode materials with desired components and architectures is a promising strategy for boosting electrochemical performance. Here, three-dimensional hierarchical ZnCo2 O4 @Ni(OH)2 core-shell nanosheet arrays have been successfully fabricated on a Ni foam substrate, in which the porous ZnCo2 O4 nanosheet "core" as the conductive scaffold was synthesized by a metal-organic framework (MOF)-templated method, and the ultrathin Ni(OH)2 nanoflakes "shell" with rich active sites were grafted on the ZnCo2 O4 nanosheet through a hydrothermal treatment. When directly used as a free-standing electrode for supercapacitor, these hierarchical ZnCo2 O4 @Ni(OH)2 core-shell nanosheet arrays exhibited a high capacitance of 3063.2 mF cm-2 (1021.1 F g-1 ) at the current density of 1 mA cm-2 . This electrode significantly outperformed individual Ni(OH)2 or ZnCo2 O4 nanosheet arrays, benefiting from the robust core-shell arrays on Ni foam with good electrical conductivity and abundant active sites, as well as the synergetic effect between MOF-derived porous ZnCo2 O4 "core" and the ultrathin Ni(OH)2 "shell". Moreover, the assembled ZnCo2 O4 @Ni(OH)2 //activated-carbon asymmetric supercapacitor displayed excellent energy and power densities (maximum of 40.0 Wh kg-1 and 8.02 kW kg-1 ) and superior cycling stability of 98.4 % retention with 91.2 % coulombic efficiency over 5 000 cycles at 10 A g-1 .

Simultaneous Modulation of Composition and Oxygen Vacancies on Hierarchical ZnCo2 O4 /Co3 O4 /NC-CNT Mesoporous Dodecahedron for Enhanced Oxygen Evolution Reaction.

Electrochemical water splitting is a promising way for the sustainable production of hydrogen, but the efficiency of the overall water-splitting reaction largely depends on the oxygen evolution reaction (OER) because of its sluggish kinetics. Herein, a series of hierarchical ZnCo2 O4 /Co3 O4 /NC-CNT (NC-CNT=nitrogen-rich carbon nanotube) mesoporous dodecahedrons grafted to carbon nanotubes have been synthesized from ZnCo bimetallic zeolitic imidazolate frameworks (ZnCo-ZIFs) through sequential pyrolysis in nitrogen and mild oxidation in air. The simultaneous modulation of oxygen vacancies, composition, and hierarchical mesoporous architecture remarkably enhanced their electronic conduction and the amount and reactivity of accessible actives; thus boosting their intrinsic activity in the OER. The optimal ZnCo2 O4 /Co3 O4 /NC-CNT-700 sample exhibited a large current density of 50 mA cm-2 at a potential of 1.65 V, a small Tafel slope of 88.5 mV dec-1 , and superior stability in alkaline media. This work should provide a facile strategy for the rational design of advanced OER catalysts by simultaneous engineering of oxygen vacancies and composition.

Self Assembled Rice Ball‐Like ZnCo2O4 Inlaid on rGO as Flexible Anodes with High Lithium Storage Capability and Superior Cycling Stability

AbstractA unique flexible configuration with ordered porous rice ball‐like ZnCo2O4 (ZCO) microspheres embedded in reduced graphene oxide (rGO) network was demonstrated by a facile solvothermal route and vacuum filtration method. As binder‐free anodes for LIBs, sandwiched structure ZCO/rGO electrode synergistically realized high lithium storage capability and good cycling stability due to enhanced conductive skeleton, robust mechanical stability and high hierarchical porosity. The ZCO/rGO hybrid depicts a reversible discharge capacity of 908.7 mAh g−1 after 500 long‐term cycles at a current density of 500 mA g−1. In addition, the flexible electrode also shows the excellent rate capacity with an average capacity of 681.8 mAh g−1 even at a large current density of 6000 mA g−1.

Self-Assembly of Three-Dimensional Zinc-Doped NiCo2 O4 as Efficient Electrocatalysts for Oxygen Evolution Reaction.

In this work, a series of three-dimensional porous flower-like zinc doped NiCo2 O4 (ZNCO) nanostructures with different Zn doping level are successfully prepared by a facile solvothermal process without using any templets. The obtained products are characterized by various techniques, and their electrocatalytic performances are also assessed by the oxygen evolution reaction (OER). According to the electrochemical characterization, it is demonstrated that ZNCO-0.15 (i.e., Zn0.15 Ni0.85 Co2 O4 ) nanoflowers show a lower overpotential, smaller Tafel slope, higher electrochemical active surface area (ECSA), as well as a larger turnover frequency (TOF) value than those of Co3 O4 , NiCo2 O4 , and ZnCo2 O4 nanoflowers, indicating that introduction of an optimal content of zinc ions plays an important role in enhancing electrocatalytic performances for OER. The enhanced OER performance of ZNCO-0.15 could be attributed to the increased number of active sites (Co3+ ), accelerated kinetic rate, and promoted conductivity of the catalyst with the incorporation of zinc ions.

Facile synthesis of porous peanut-like ZnCo2O4 decorated with rGO/CNTs toward high-performance lithium ion batteries

In this work, we develop an effective strategy to synthesize porous peanut-like ZnCo2O4 (ZCO) decorated with graphene/Carbon nanotubes (CNTs) as an effective anode material for long cycling life lithium storage via a facile solvothermal process and rapid cold-quenching method. SEM and TEM characterizations show that graphene and CNTs serving as the elastic support and superior conductive network wrap the porous peanut-like ZCO, which can enhance electrochemical performance. The as-prepared ZnCo2O4/reduce graphene oxide/carbon nanotubes (ZCO/rGO/CNTs) delivers an initial discharge capacity of 1214.1 mAh g−1 at a current density of 500 mA g−1 and exhibits a high discharge capacity (1026.6 mAh g−1 after 200 cycles) when evaluated as anode materials of LIBs. More interestingly, the reversible capacity of the ZCO/rGO/CNTs even retains 728.6 mAh g−1 after 300 cycles even at a high current density of 1000 mA g−1. The good cycling capability, high rate performance and reliable electrode adaptability suggest that the ZCO/rGO/CNTs will be an attractive material for lithium ion batteries.

Three-Dimensional Hierarchically Mesoporous ZnCo2 O4 Nanowires Grown on Graphene/Sponge Foam for High-Performance, Flexible, All-Solid-State Supercapacitors.

To achieve high energy storage on three-dimensional (3D) structures at low cost, materials with high power and long cycle life characteristics have to be developed. We synthesized ZnCo2 O4 /reduced graphene oxide (rGO) binary composites in commercial sponges. ZnCo2 O4 nanosheets were grown on the surface of GO/sponge through a hydrothermal reaction. The resulting flexible, free-standing ZnCo2 O4 /rGO/sponge electrodes were used as the electrodes in a symmetric supercapacitor. ZnCo2 O4 /rGO/sponge electrodes have a large specific capacitance of 1116.6 F g-1 at a scan rate of 2 mV s-1 in aqueous electrolyte. The all-solid-state flexible supercapacitor is assembled based on ZnCo2 O4 /rGO/sponge electrodes, which show excellent electrochemical performances with a specific capacitance of 143 F g-1 at a current density of 1 A g-1 . The as-fabricated supercapacitor also exhibits excellent cycling stability (93.4 % capacitance retention after 5000 cycles) and exceptional mechanical flexibility. These results demonstrate the potential of ZnCo2 O4 /rGO/sponge as an electrode in flexible, high-performance supercapacitors.