NiCo2O4 Nanowire Arrays Research Articles

Surface modulation of NiCo2O4 nanowire arrays with significantly enhanced reactivity for ultrahigh-energy supercapacitors

Ternary NiCo2O4 is attracting substantial attention as electrode material for high-performance supercapacitors. Unfortunately, it still suffers from low specific capacitance in terms of its relative low conductivity. Herein, an effective and general surface modulation strategy involving in-situ phosphatization of NiCo2O4 nanowire arrays is developed, and the pseudopotential performance of the resulting NiCo2O4 nanowire arrays is dramatically increased. The surface modulation can increase active sites, enhance conductivity and accelerate charge transfer kinetics. Importantly, at a large current density of 20 A g−1, the optimal NiCo2O4 electrode possesses a significant specific capacitance of 1642 F g−1. When the current density increases from 2 to 20 A g−1, an excellence rate capability with 81.3% specific capacitance is maintained. Also, the resulting electrode owns excellent long-term cycle stability that the specific capacitance only decreases 4.3% after 10,000 cycles. Moreover, an advanced asymmetric supercapacitor device is build up based on the optimal NiCo2O4 cathode and a graphene anode, reaching an outstanding energy density of 92.2 Wh kg−1 with outstanding long-term durability.

Surface phosphation of 3D mesoporous NiCo2O4 nanowire arrays as bifunctional anodes for lithium and sodium ion batteries.

A novel surface phosphate strategy was adopted to dramatically improve the charge transport, ion diffusion, electroactive sites, and cycle stability of mesoporous NiCo2O4 nanowire arrays (NWAs), drastically boosting their electrochemical properties. Consequently, the as-prepared phosphated NiCo2O4 NWA (P-NiCo2O4 NWA) electrode achieved excellent energy storage performance as a bifunctional anode material for both lithium ion batteries (LIBs) and sodium ion batteries (SIBs). When evaluated as an anode for LIBs, this P-NiCo2O4 NWA electrode showed a high reversible capacity up to 1156 mA h g−1 for 1500 cycles at 200 mA g−1 without appreciable capacity attenuation, while in SIBs, the electrode could also deliver an admirable initial capacity as high as 687 mA h g−1 and maintained 83.5% of this after 500 cycles at the same current density. Most important, when the current density increased from 100 to 1000 mA g−1, the capacity retention was about 63% in LIBs and 54% in SIBs. This work may shed light on the engineering of efficient electrodes for multifunctional flexible energy storage device applications.

CeO2@NiCo2O4 nanowire arrays on carbon textiles as high performance cathode for Li-O2 batteries

The successful development of Li-O2 battery technology depends on developing a stable and efficient cathode. As an important step toward this goal, for the first time, we report the development of CeO2 nanoparticles modified NiCo2O4 nanowire arrays (NWAs) grown on the carbon textiles as a new carbon-free and binder-free cathode system. In this study, the Li-O2 battery with the CeO2@NiCo2O4 NWAs has exhibited much reduced overpotentials, a high discharge capacity, an improved cycling stability, outperforming the Li-O2 battery with NiCo2O4 NWAs. These improvements can be attributed to both the tailored morphology of discharge product and improved oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) activity after CeO2 NPs deposition. To a considerable extent, this idea of cathode construction including structure design and composition optimization can provide guidance for further researches in developing more powerful cathode for Li-O2 battery.

Hydrogen evolution activity enhancement by tuning the oxygen vacancies in self-supported mesoporous spinel oxide nanowire arrays

The development of facile strategies to tune the oxygen vacancy (OV) content in transition metal oxides (TMOs) is paramount to obtain low-cost and stable electrocatalysts, but still highly challenging. Taking NiCo2O4 as a model system, we have experimentally established a facile calcination and electrochemical activation (EA) methodology to dramatically increase the concentration of OVs and provide theoretical insight into how the concentration of OVs affects the performance of spinel TMOs towards the electrochemical hydrogen evolution reaction (HER). A self-supported cathode of OV-rich NiCo2O4 nanowire arrays was found to exhibit higher HER activity and better stability in alkaline media than its counterparts with fewer OVs. The electrocatalytic HER activity was in good agreement with the increasing concentration of OVs in the studied samples. A large current density of 360 mA·cm–2 was reached with an overpotential of only 317 mV. Additionally, such a facile strategy was able to efficiently generate OVs in other TMOs (e.g., CoFe2O4 and NiFe2O4) for enhanced HER performance. In addition, our theoretical results suggest that the increasing OV concentration reduces the adsorption energy of water molecules and their dissociation energy barrier on the surface of the catalyst, thus leading to performance improvement of spinel TMOs toward the electrochemical HER. This work may open a new avenue to increase the concentration of OVs in TMOs in a controlled manner for promising applications in a variety of fields.

Coupling Molecularly Ultrathin Sheets of NiFe-Layered Double Hydroxide on NiCo2O4 Nanowire Arrays for Highly Efficient Overall Water-Splitting Activity.

Developing efficient but nonprecious bifunctional electrocatalysts for overall water splitting in basic media has been the subject of intensive research focus with the increasing demand for clean and regenerated energy. Herein, we report on the synthesis of a novel hierarchical hybrid electrode, NiFe-layered double hydroxide molecularly ultrathin sheets grown on NiCo2O4 nanowire arrays assembled from thin platelets with nickel foam as the scaffold support, in which the catalytic metal sites are more accessible and active and most importantly strong chemical coupling exists at the interface, enabling superior catalytic power toward both oxygen evolution reaction (OER) and additionally hydrogen evolution reaction (HER) in the same alkaline KOH electrolyte. The behavior ranks top-class compared with documented non-noble HER and OER electrocatalysts and even comparable to state-of-the-art noble-metal electrocatalysts, Pt and RuO2. When fabricated as an integrated alkaline water electrolyzer, the designed electrode can deliver a current density of 10 mA cm-2 at a fairly low cell voltage of 1.60 V, promising the material as efficient bifunctional catalysts toward whole cell water splitting.

Hierarchical Porous Nickel Cobaltate Nanoneedle Arrays as Flexible Carbon-Protected Cathodes for High-Performance Lithium-Oxygen Batteries.

Rechargeable lithium-oxygen (Li-O2) batteries are consequently considered to be an attractive energy storage technology because of the high theoretical energy densities. Here, an effective binder-free cathode with high capacity for Li-O2 batteries, needle-like mesoporous NiCo2O4 nanowire arrays uniformly coated on the flexible carbon textile have been in situ fabricated via a facile hydrothermal process followed by low temperature calcination. Because of the material and structural features, the needle-like NiCo2O4 nanowire arrays (NCONWAs) served as a binder-free cathode exhibits high specific capacity (4221 mAh g(-1)), excellent rate capability, and outstanding cycling stability (200 cycles). This cathode based on nonprecious mesoporous metal oxides nanowire arrays has large open spaces and high surface area, providing numerous catalytically active sites and effective transmission pathways for lithium ion and oxygen, and promises the abundant Li2O2 storage. The fast electron transport by directly anchoring on the substrate ensures fast electrochemical reaction process involved with the every nanowire. Furthermore, a bendable Li-O2 battery assembled by using the flexible NCONWAs as the cathode, can be able to light an LED and shows good rate capability and cyclic stability.

Rationally Designed Carbon Fiber@NiCo2O4@Polypyrrole Core–Shell Nanowire Array for High-Performance Supercapacitor Electrodes

The composite supercapacitor electrodes were rationally fabricated by facile electrochemical deposition of polypyrrole (PPy) on NiCo2O4 nanowire arrays which were grown radially on carbon fiber (CF). When used as electrodes in supercapacitors, the composite nanostructures demonstrated prominent electrochemical performances with a high areal capacitance (1.44[Formula: see text]F/cm2 at a current density of 2[Formula: see text]mA/cm2), a good rate capability (80.5% when the current density increases from 2[Formula: see text]mA/cm2 to 20[Formula: see text]mA/cm2), and a good cycling ability (85% of the initial specific capacitance remained after 5000 cycles at a high current density of 10[Formula: see text]mA/cm2). The excellent electrochemical performance of NiCo2O4@PPy nanostructures can be mainly ascribed to the good electrical conductivity of PPy, the enhanced adherent force between electrode materials and CF to hold the electrode fragments together by means of NiCo2O4 nanowires, the short ion diffusion pathway in ordered porous NiCo2O4 nanowires and the three-dimensional nanostructures.

Three-Dimensional NiCo2O4@Polypyrrole Coaxial Nanowire Arrays on Carbon Textiles for High-Performance Flexible Asymmetric Solid-State Supercapacitor.

In this article, we report a novel electrode of NiCo2O4 nanowire arrays (NWAs) on carbon textiles with a polypyrrole (PPy) nanosphere shell layer to enhance the pseudocapacitive performance. The merits of highly conductive PPy and short ion transport channels in ordered NiCo2O4 mesoporous nanowire arrays together with the synergistic effect between NiCo2O4 and PPy result in a high specific capacitance of 2244 F g(-1), excellent rate capability, and cycling stability in NiCo2O4/PPy electrode. Moreover, a lightweight and flexible asymmetric supercapacitor (ASC) device is successfully assembled using the hybrid NiCo2O4@PPy NWAs and activated carbon (AC) as electrodes, achieving high energy density (58.8 W h kg(-1) at 365 W kg(-1)), outstanding power density (10.2 kW kg(-1) at 28.4 W h kg(-1)) and excellent cycling stability (∼89.2% retention after 5000 cycles), as well as high flexibility. The three-dimensional coaxial architecture design opens up new opportunities to fabricate a high-performance flexible supercapacitor for future portable and wearable electronic devices.

One-dimensional NiCo2O4 nanowire arrays grown on nickel foam for high-performance lithium-ion batteries

With the ever-increasing power and energy needs in application of advanced consumer electronics and related technologies, developing electrode materials with both high energy and power densities holds the key for satisfying the urgent demand of energy storage worldwide. Herein, we report the successful preparation of NiCo2O4 nanowire arrays that are grown on nickel foam via a simple hydrothermal method followed by an annealing process. The electron microscopy images of the obtained NiCo2O4 nanowires reveal that the NiCo2O4 nanowires are uniformly distributed and anchored on the surface of nickel foam. Benefited from the unique structure of NiCo2O4 nanowires on a nickel foam substrate, the as prepared materials exhibit a high reversible capacity of 1048.8 mAh g−1 at 100 mA g−1 and show excellent rate performance for lithium storage.

Effect of temperature on pseudocapacitance performance of carbon fiber@NiCo2O4@Ni(OH)2 core–shell nanowire array composite electrodes

The composite supercapacitor electrodes are fabricated by facile electrochemical deposition of Ni(OH)2 nanosheets on NiCo2O4 nanowire arrays which are grown radially on carbon fiber. The composite electrodes offer specific capacitance of 2400F/g at 1mA/cm2, excellent rate capability of 89% as the current density increasing from 1 to 20mA/cm2. Electrochemical performances are investigated at different temperatures from 0°C to 60°C. The specific capacitance at 1mA/cm2 increases from 2100F/g at 0°C to 3000F/g at 60°C. The mechanisms of effect of temperature on the electrochemical properties of the composite electrode are investigated. This study provides a fundamental comprehension of the temperature dependent of composite electrodes.

One dimensionally spinel NiCo2O4 nanowire arrays: facile synthesis, water oxidation, and magnetic properties

Development of efficient, affordable, non-precious metal oxides catalysts is critical for the oxygen evolution reaction (OER). Herein, we present a spinel NiCo2O4 nanowire arrays (NWAs), synthesized by a simple solution route, as an inexpensive, efficient anode electrocatalyst for water electrolysis. The as-prepared NiCo2O4 NWAs contains Ni2+/Ni3+ which replace Co in octahedral sites of the spinel Co3O4, exhibiting higher catalytic activity than that of Co3O4 and NiO. The enhanced catalytic activity of NiCo2O4 NWAs is correlated with a large surface area, one-dimensional (1D) architecture, high conductivity and synergistic behavior of Ni/Co bifunctional catalyst. Besides, oxygen vacancies, which favor efficient electrons transport, supply more active sites, and assist in the adsorption of OH−, can be conducive to make high utilization of catalytic materials in the OER. Moreover, the magnetic properties of NiCo2O4 NWAs are also investigated in detail. The results indicate that NiCo2O4 NWAs could be a promising economical and environmentally benign bifunctional electrocatalyst for water splitting and other applications.

Heterogeneous NiCo2O4@polypyrrole core/sheath nanowire arrays on Ni foam for high performance supercapacitors

A novel heterogeneous NiCo2O4@PPy core/sheath nanowire arrays are directly grown on Ni foam involving three facile steps, hydrothermal synthesis and calcination of NiCo2O4 nanowire arrays and subsequent in-situ oxidative polymerization of polypyrrole (PPy). When investigated as binder- and conductive additive-free electrodes for supercapacitors (SCs) in 6 M KOH, the NiCo2O4@PPy core/sheath nanowire arrays exhibit high areal capacitance of 3.49 F cm−2 at a discharge current density of 5 mA cm−2, which is almost 1.5 times as much as the pristine NiCo2O4 (2.30 F cm−2). More importantly, it can remain 3.31 F cm−2 (94.8% retention) after 5000 cycles. The as-obtained electrode also displays excellent rate capability, whose areal capacitance can still remain 2.79 F cm−2 while the discharge current density is increased to 50 mA cm−2. The remarkable electrochemical performance is mainly attributed to the unique heterogeneous core/sheath nanowire-array architectures.

Freestanding eggshell membrane-based electrodes for high-performance supercapacitors and oxygen evolution reaction.

A type of freestanding, light-weight eggshell membrane-based electrode is demonstrated for supercapacitors and for oxygen evolution reaction (OER) catalysis. As a widely available daily waste, eggshell membranes have unique porous three-dimensional grid-like fibrous structures with relatively high surface area and abundant macropores, allowing for effective conjugation of carbon nanotubes and growth of NiCo2O4 nanowire arrays, an effective supercapacitor material and OER catalyst. The three-dimensional fibrous eggshell membrane frameworks with carbon nanotubes offer efficient pathways for charge transport, and the macropores between adjacent fibers are fully accessible for electrolytes and bubble evolution. As a supercapacitor, the eggshell membrane/carbon nanotube/NiCo2O4 electrode shows high specific capacitances at current densities from 1 to 20 A g(-1), with excellent capacitance retention (>90%) at 10 A g(-1) for over 10,000 cycles. When employed as an OER catalyst, this eggshell membrane-based electrode exhibits an OER onset potential of 1.53 V vs. the reversible hydrogen electrode (RHE), and a stable catalytic current density of 20 mA cm(-2) at 1.65 V vs. the RHE.

Hierarchical NiCo2O4 nanowire arrays on Ni foam as an anode for lithium-ion batteries

A facile two-step method is developed for large-scale growth of hierarchical mesoporous NiCo2O4 nanowire arrays on Ni foam with robust adhesion as a high performance electrode for lithium-ion batteries (LIBs).

Metal Oxides: Mesoporous NiCo2O4 Nanowire Arrays Grown on Carbon Textiles as Binder‐Free Flexible Electrodes for Energy Storage (Adv. Funct. Mater. 18/2014)

Metal Oxides: Mesoporous NiCo₂O₄ Nanowire Arrays Grown on Carbon Textiles as Binder‐Free Flexible Electrodes for Energy Storage (Adv. Funct. Mater. 18/2014)

Direct growth of porous crystalline NiCo2O4 nanowire arrays on a conductive electrode for high-performance electrocatalytic water oxidation

Herein we report a facile and direct synthesis of porous NiCo2O4 nanowire arrays (NWAs) with robust mechanical adhesion to conductive electrodes by a simple two-step method for efficient water oxidation.

Mesoporous NiCo2O4 Nanowire Arrays Grown on Carbon Textiles as Binder‐Free Flexible Electrodes for Energy Storage

Binary metal oxides has been regarded as a promising class of electrode materials for high‐performance energy storage devices since it offers higher electrochemical activity and higher capacity than mono‐metal oxide. Besides, rational design of electrode architectures is an effective solution to further enhance electrochemical performance of energy storage devices. Here, the advanced electrode architectures consisting of carbon textiles uniformally covered by mesoporous NiCo2O4 nanowire arrays (NWAs) are successfully fabricated by a simple surfactant‐assisted hydrothermal method combined with a short post annealing treatment, which can be directly applied as self‐supported electrodes for energy storage devices, such as Li‐ion batteries, supercapacitors. The as‐prepared mesoporous NiCo2O4 nanowires consist of numerous highly crystalline nanoparticles, leaving a large number of mesopores to alleviate the volume change during the charge/discharge process. Electrode architectures presented here promise fast electron transport by direct connection to the growth substrate and facile ion diffusion path provided by both the abundant mesoporous structure in nanowires and large open spaces between neighboring nanowires, which ensures every nanowire participates in the ultrafast electrochemical reaction. Benefiting from the intrinsic materials and architectures features, the unique binder‐free NiCo2O4/carbon textiles exhibit high specific capacity/capacitance, excellent rate capability, and cycling stability.

NiCo2O4 nanowire arrays supported on Ni foam for high-performance flexible all-solid-state supercapacitors

Portable electronic devices which are ultrathin, lightweight and even able to roll-up have attracted much attention. Herein, we report the design of flexible all-solid-state symmetric supercapacitors by using two NiCo2O4 nanowire arrays supported on Ni foams as the electrodes. The as-fabricated symmetric supercapacitors have excellent electrochemical performance with a high cell areal capacitance of 161 mF cm−2 at 1 mA cm−2. Good electrochemical performance stability over 3000 cycles was obtained even when the device was under harsh mechanical conditions including both twisted and bent states. As-fabricated all-solid-state supercapacitors could be charged and power a commercial light-emitting-diode, demonstrating their feasibility as an efficient energy storage component and self-powered micro/nano-system. In addition, we were able to grow NiCo2O4 nanowire arrays on many kinds of flexible substrates, including nickel foam, carbon cloth, Ti foil and polytetrafluoroethylene tape. Our work here opens up opportunities for the device configuration for energy-storage devices in the future wearable electronic area and many other flexible, lightweight and high performance functional nanoscale devices.

Supercapacitance of NiCo<sub>2</sub>O<sub>4</sub> Nanowire Arrays Grown on Nickel Foam

We prepared an electrode consisting of NiCo2O4 nanowire arrays that stand freely on nickel foam by a template-free growth method.Its morphology was determined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM).The phase structure of the nanowires was analyzed by X-ray diffraction (XRD).The supercapacitance of the electrode was investigated by cyclic voltammetry,galvanostatic charge-discharge testing,and electrochemical impedance spectroscopy.The results showed that the nanowires were nearly vertical grow on and densely cover the nickel foam substrate.The nanowires have diameters around 500-1000 nm and lengths up to around 10 μm.The NiCo2O4 nanowire arrays have a specific capacitance of 741 F · g-1 and this value is 655 F · g-1 after 420 charge-discharge cycles.Electrochemical impedance spectroscopy measurements showed that the charge transfer resistance was only 0.33 Ω and this increased by only 0.06 Ω after 420 cycles.