Co3O4 Nanoneedles Research Articles

Phase and morphology evolution of high dielectric CoO/Co3O4 particles with Co3O4 nanoneedles on surface for excellent microwave absorption application

Novel dual phased CoO/Co3O4 particles with Co3O4 nanoneedles on surface are obtained by annealing dual-phased Co (hexagonal and cubic phases) particles. Their phase and morphology evolution are clarified by XRD, SEM and TEM measurements. The early formed CoO and Co3O4 on surface from dual-phased Co promote the outdiffusion process of inside Co with kirkendall effect and restrict the growth of Co3O4 with a specific orientation, leading to the formation of Co3O4 nanoneedles on the surface. The microwave absorption measurement shows that the CoO/Co3O4 particles with annealing time of 1 h possess higher permittivity and better performances than pure Co and Co3O4 particles. An enhanced reflection loss (RL) value of −38.8 dB is obtained for the CoO/Co3O4-paraffin wax (PW) composite with a thickness of 2.8 mm. The absorption bandwidth for RL below −10 dB reaches 8.7 GHz. The Co3O4 nanoneedles on surface, porous structure and inner dual phased CoO/Co3O4 bring increased multiple reflection, interface/dipolar polarizations, conductive loss and better impedance matching. This clarification of phase and morphology evolution and novel CoO/Co3O4 material with nanoneedles on surface may provide new routes for designing high performance Co-based microwave absorbers with unique structures.

Electrochemical deposition of CeO2 nanocrystals on Co3O4 nanoneedle arrays for efficient oxygen evolution

In this work, we report an efficient catalyst for oxygen evolution reaction based on CeO2 nanoparticles modified Co3O4 nanoneedle arrays directly grown on copper foam. Cobalt hydroxyl carbonate (CoHC) nanoneedle arrays are grown on Cu foam by a hydrothermal method. Using an electrochemical deposition method, Ce(OH)3 is deposited on the surface of the CoHC nanoneedles, which is converted into CeO2 modified Co3O4 with the same morphology by simple calcination in air. Excellent catalytic performance for the oxygen evolution reaction is observed, featured for the low overpotential of only 334 mV at 10 mA cm−2 in 1 M KOH. The enhanced OER performance is attributed to the variable Ce oxidation number and oxygen vacancy in CeO2. The results demonstrate the positive effect of CeO2 for the oxygen evolution reaction which was largely ignored in previous study.

Sea urchin-like Co3O4@Pd Nanoneedles with 3D open-structured matrix as efficient catalytic cathode for Li-O2 batteries

In this study, both morphology-related factors and catalytic activity factors were taken into account simultaneously and sea urchin-like Co3O4 nanoneedles grown on nickel foam were synthesized via a facile hydrothermal strategy (grass-like Co3O4 were also prepared for comparison). Most noteworthy is that 3D open-structured sea urchin-like Co3O4 exposing more Co3+ sites with large specific surface area and abundant mesoporous structure exhibited superior electrocatalytic performance as compared to 1D structured grass-like Co3O4 and former reported 3D structured electrodes (i.e., urchin shaped, flower shaped). Pd decorated sea urchin-like Co3O4 was also prepared through a simple impregnationmethod. When served as binder/carbon-free catalytic cathode for Li-O2 batteries, the problems about limited capacity, large overpotential and poor cycle life were effectively improved. The catalytic electrode displayed a low overpotential of 1.12 V, high specific capacity (8819.2 mA h g−1) at a current density of 200 mA g−1 and long cycle life with the capacity limited at 500, 1500, 2500, even 3500 mA h g−1, overmatching most of the transition-metal-oxides based catalytic electrodes, which are intrinsically dependent on the characteristic design in both morphology and catalytic active sites of the electrodes.

High-temperature stable refractory nanoneedles with over 99% solar absorptance

Solar absorber coatings have widely been investigated for solar-thermal technologies including concentrated solar power and solar thermochemistry. While various nanostructures such as nanowires and nanotubes have been commonly used for high solar absorptance owing to their potent light trapping effect, the high temperature stability of these nanostructures has yet to be established due to either coarsening of nanostructures or oxidation of certain materials in air (e.g., Si and C). In this work, we developed a nanostructured solar absorber from a family of high-temperature refractory spinel oxides, Co3O4 and CuCo2O4, with ultra-high solar absorptance over 99%. Once coated with a thin layer of HfO2 or SiO2 through atomic layer deposition, the Co3O4 and CuCo2O4 nanoneedles preserve their high aspect ratio and sharp tips, allowing the solar absorbers to maintain the superior absorptivity and excellent thermal stability at an elevated temperature for an extended period (650 °C and 800 °C for 100 h for passivated Co3O4 and Cu1Co2O4, respectively). These results suggest that solar absorbers made from refractory spinel oxide nanoneedles can be used for high-temperature solar thermal applications with ultrahigh absorptance.

Multilayer Network Membranes Based on Evenly Dispersed Nanofibers/Co3O4 Nanoneedles for High‐Efficiency Separation of Micrometer‐Scale Oil/Water Emulsions

AbstractUltrawetting membranes have enabled great progress in oil/water separation and have helped to address global industrial wastewater pollution and marine oil spills. However, there are few reports of 3D multilayer network membranes that can be easily prepared, and give efficient separation in micro‐ and nanoscale oil‐in‐water emulsions. A membrane is designed for emulsion separation; it consists of ultralong (over 10 µm) sodium titanate nanofibers as the selective layer and a jungle‐like Co3O4 nanoneedles mesh as the support layer. This mesh shows superhydrophilicity in air and low‐adhesive superoleophobicity under water. This membrane gives 99.9% separation efficiency and good permeation flux, and has great advantages in the separation under gravity of oil‐in‐water emulsions with droplet sizes larger than 400 nm. The results of this work provide a new method for designing ultrathin, efficient, and durable separation membranes with a 3D multilayer network structure.

Two-step growth mechanism of supported Co3O4-based sea-urchin like hierarchical nanostructures

Supported 3D hierarchical nanostructures of transition metal oxides exhibit enhanced photocatalytic performances and long-term stability under working conditions. The growth mechanisms crucially determine their intimate structure, that is a key element to optimize their properties. We report on the formation mechanism of supported Co3O4 hierarchical sea urchin-like nanostructured catalyst, starting from Co-O-B layers deposited by Pulsed Laser Deposition (PLD). The particles deposited on the layer surface, that constitute the seeds for the urchin formation, have been investigated after separation from the underneath deposited layer, by X-ray diffraction, X-ray absorption spectroscopy and scanning electron microscopy. The comparison with PLD deposited layers without O and/or B indicates a crucial role of B for the urchin formation that (i) limits Co oxidation during the deposition process and (ii) induces a chemical reduction of Co, especially in the particle core, in the first step of air annealing (2 h, 500 °C). After 2 h heating Co oxidation proceeds and Co atoms outdiffuse from the Co fcc particle core likely through fast diffusion channel present in the shell and form Co3O4 nano-needles. The growth of nano-needles from the layer beneath the particles is prevented by a faster Co oxidation and a minimum fraction of metallic Co. This investigation shows how diffusion mechanisms and chemical effects can be effectively coupled to obtain hierarchical structures of transition metal oxides.

Fabrication of Isomorphous Co3 O4 @Co3 O4 Hierarchical Core-Shell Nanoneedles for High-Performance Supercapacitors

Isomorphous Co3O4@Co3O4 core-shell hierarchical nanoneedles are fabricated through a simple two-step hydrothermal process associated with an annealing treatment. The unique nanoarchitecture consists of a layer of isomorphous Co3O4 nanosheets well coated on the surface of Co3O4 nanoneedles. The isomorphous Co3O4@Co3O4 core-shell hierarchical nanostructures exhibit a remarkable capacitance of 973.6 F g−1 at a current density of 1 A g−1 owing to the isomorphous core-shell hierarchical architecture and porous feature. Moreover, an asymmetric supercapacitor device based on the hierarchical Co3O4@Co3O4 core-shell nanostructure and porous carbon is fabricated and exhibits a desirable high energy densities with a value of 137.96 Wh kg−1 at a power density of 0.32 kW kg−1. These results indicate that the as-prepared nanomaterials are outstanding candidates for electrochemical supercapacitors.

Co3O4 nanoneedle@electroactive nickel boride membrane core/shell arrays: A novel hybrid for enhanced capacity

Exploring novel hybrid materials with efficient microstructure using facile approaches is highly urgent in designing supercapacitor electrodes. Here, the Ni-B membrane was used for coating the porous Co3O4 nanoneedle arrays which supported on the nickel foam (NF) frameworks through a rapid chemical reduction process (denoted as NF/Co3O4@NiB). The Ni-B membrane both provided sufficient active sites for redox reactions and inhibited the aggregation of formed hybrid architectures. Benefiting from the unique structural design and strongly coupled effects between porous Co3O4 arrays and Ni-B membrane, the resulted NF/Co3O4@NiB electrode exhibited high areal capacitance of 3.47Fcm−2 (0.48mAhcm−2) at a current density of 2.5mAcm−2, an excellent rate capability while maintaining 95.5% capacity retention after 2000 cycles. The asymmetric supercapacitor constructed with the NF/Co3O4@NiB as positive electrode and hierarchical porous carbon (HPC) as negative electrode also showed ideal capacitive behavior, and simultaneously delivered high energy and power densities. The easily decoration of Ni-B membrane on various active nanoarrays may arouse more novel design about hybrid architectures for large-scale applications.

Correction: Self-supported Co3O4 nanoneedle arrays decorated with PPy via chemical vapor phase polymerization for high-performance detection of trace Pb2+

Correction for ‘Self-supported Co3O4 nanoneedle arrays decorated with PPy via chemical vapor phase polymerization for high-performance detection of trace Pb2+’ by Wenjing Wang et al., Anal. Methods, 2017, 9, 1905–1911.

Perforated Co3O4 nanoneedles assembled in chrysanthemum-like Co3O4 structures for ultra-high sensitive hydrazine chemical sensor

Herein, we report the successful synthesis of chrysanthemum-like Co3O4 structures composed of high-aspect ratio perforated Co3O4 nanoneedles. The chrysanthemum-like Co3O4 structures were obtained by the heat treatment of cobalt-carbonate-hydroxide (Co(CO3)0.5(OH)·0.11H2O) chrysanthemum structures which were prepared by simple and facile hydrothermal process. The prepared materials were characterized using several techniques which confirmed that the prepared materials, i.e. precursor Co(CO3)0.5(OH)·0.11H2O and Co3O4, both possess chrysanthemum-like morphologies which are made by the accumulation of radially oriented nanoneedles. The prepared chrysanthemum-like Co3O4 structures were further used as electron mediators to fabricate highly sensitive and selective hydrazine (N2H4) chemical sensors. The sensitivity, detection limit, linear range, selectivity, repeatability, and reproducibility of such fabricated chrysanthemum-like Co3O4 structures base hydrazine chemical sensor was comprehensively investigated. It was observed that the sensing of the fabricated sensors are highly dependent on the morphology of Co3O4, and the chrysanthemum-like Co3O4 structures exhibited the best sensing performance. Further, a good repeatability and reproducibility, longtime stability and great selectivity both in amperometric and voltammetric chrysanthemum-like Co3O4 structures based sensors were observed. The detailed sensing results confirmed that the fabricated chemical sensor exhibited a high sensitivity of 107.9μAmM−1, a detection limit of 3.7μM and a linear range of 50–1088μM. The observed results demonstrate that the synthesized chrysanthemum-like Co3O4 offers a promising probe candidate for the fabrication of highly sensitive and selective chemical sensors.

Magnetic-field-assisted synthesis of Co3O4 nanoneedles with superior electrochemical capacitance

Nanostructured Co3O4 films have been deposited on nickel foam in a magnetic-field-assisted hydrothermal process followed by annealing in air. The magnetic field strength is varied to study its relationship with nanostructures, morphology, and electrochemical properties of the Co3O4 electrodes. The Co3O4 films synthesized in the weak magnetic fields consist of dispersed nanoneedles, which are different from clustered nanoneedles when the magnetic field is absent. Moreover, the magnetic fields (of several millitesla) induced substantial changes in the nanostructures and electrochemical properties of the Co3O4 films. A possible formation mechanism of Co3O4 nanoneedles is proposed by comparing the morphologies and nanostructures of the films synthesized with and without the magnetic fields. Among these electrodes, the optimal one has a high specific capacitance (970.8 F g−1 at 0.5 A g−1), good power capability (847.5 F g−1 at 6.0 A g−1), and an excellent retention ratio (93.7 % over 1000 cycles). All these impressive results demonstrate that magnetic fields may be an economic and effective tool in hydrothermal synthesis of Co3O4 electrodes for high-performance supercapacitors.

Effect of microwave power on the thermal genesis of Co3O4 nanoparticles from cobalt oxalate micro-rods

This study focuses on investigating the influence of microwave power (MWP) change on the morphology and size of Co3O4 nanoparticles (NPs), which was obtained from the thermal decomposition of cobalt oxalate precursor. The oxalate precursor was prepared via the microwave-assisted route in the presence of cetyltrimethylammonium bromide (CTAB) employing an MWP of 280 and 700W. Physicochemical properties of the prepared solids were characterized by means of X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and thermogravimetry-differential thermal analyses (TGA-DTA). The results obtained indicated that the applied MWP has a crucial effect in controlling the morphology and the size of CoC2O4·2H2O as well as Co3O4 NPs. Acicular- and rod-like morphologies of both phases were obtained employing an MWP of 280 and 700W during the preparation, respectively. Further, both the prepared Co3O4 nanoneedles and nanorods are composed of net-like structure of interconnected nanocapsules. Moreover, although all the routes led to the same phase, additional difference existed in terms of surface Co2+ and hydroxyl-carbonate concentrations. Lower MWP favors high Co2+ and low cobalt hydroxyl-carbonate surface concentrations.

Mesoporous Co3O4 nanoneedle arrays for high-performance gas sensor

Co3O4 nanoneedle arrays were successfully fabricated via a facile two-step approach, including the formation of needle-shaped Co(CO3)0.5(OH)·0.11H2O followed by thermal conversion to mesoporous Co3O4. The Co3O4 nanoneedle arrays exhibit mesoporosity and quasi-single-crystalline structure, and can directly serve as gas sensors without the conventional film formation process, owing to the directly growth on the substrates and good ohmic contact with the electrodes. The Co3O4 nanoneedle arrays-based gas sensor showed high performance in ethanol detection. The highest sensitivity reached ∼89.6 for 100ppm ethanol vapor and the optimal working temperature was as low as 130°C. The high performance attributes to the unique structure of nanoneedle arrays with a variety of favorable features. More attractively, we find the special exposed crystal planes of Co3O4 affect the gas-sensing properties significantly.

Three‐Dimensional Co3O4@MnO2 Hierarchical Nanoneedle Arrays: Morphology Control and Electrochemical Energy Storage

In this paper, a highly ordered three‐dimensional Co3O4@MnO2 hierarchical porous nanoneedle array on nickel foam is fabricated by a facile, stepwise hydrothermal approach. The morphologies evolution of Co3O4 and Co3O4@MnO2 nanostructures upon reaction times and growth temperature are investigated in detail. Moreover, the as‐prepared Co3O4@MnO2 hierarchical structures are investigated as anodes for both supercapacitors and Li‐ion batteries. When used for supercapacitors, excellent electrochemical performances such as high specific capacitances of 932.8 F g−1 at a scan rate of 10 mV s−1 and 1693.2 F g−1 at a current density of 1 A g−1 as well as long‐term cycling stability and high energy density (66.2 W h kg−1 at a power density of 0.25 kW kg−1), which are better than that of the individual component of Co3O4 nanoneedles and MnO2 nanosheets, are obtained. The Co3O4@MnO2 NAs are also tested as anode material for LIBs for the first time, which presents an improved performance with high reversible capacity of 1060 mA h g−1 at a rate of 120 mA g−1, good cycling stability, and rate capability.

Seed-assisted synthesis of Co3O4@α-Fe2O3 core–shell nanoneedle arrays for lithium-ion battery anode with high capacity

A novel hierarchical Co3O4@α-Fe2O3 core–shell nanoneedle array (Co3O4@α-Fe2O3 NAs) on nickel foam substrate is synthesized successfully by a stepwise, seed-assisted, hydrothermal approach. This composite nanostructure serving as an anode material for lithium-ion batteries (LIBs) is advantageous in providing large interfacial area for lithium insertion/extraction and short diffusion pathways for electronic and ionic transport. The results show that a high initial discharge capacity of 1963 mA h g−1 at 120 mA g−1 was obtained by using these hierarchical Co3O4@α-Fe2O3 NAs heterostructures as an anode, and is retained at 1045 mA h g−1 after 100 cycles, better than that of pure Co3O4 nanoneedle arrays (Co3O4 NAs) and α-Fe2O3 film grown under similar conditions, indicating a positive synergistic effect of the material and structural hybridization on the enhancement of the electrochemical properties. The fabrication strategy presented here is facile, cost-effective, and scalable, which opens new avenues for the design of optimal composite electrode materials with improved performance.

Porous Co3O4 nanoneedle arrays growing directly on copper foils and their ultrafast charging/discharging as lithium-ion battery anodes

Ultrafast charging/discharging of lithium-ion battery anodes is realized from porous Co(3)O(4) nanoneedle arrays growing on copper foils. Their charge time can be shortened to ∼6 s, their reversible capacity at 0.5C rate is 1167 mAh/g. This implies that nano-arrays growing directly on copper foils are good candidates for anodes.

Thermal formation of mesoporous single-crystal Co3O4 nano-needles and their lithium storage properties

In this work, we report the simple solid-state formation of mesoporous Co3O4 nano-needles with a 3D single-crystalline framework. The synthesis is based on controlled thermal oxidative decomposition and re-crystallization of precursor β-Co(OH)2 nano-needles. Importantly, after thermal treatment, the needle-like morphology can be completely preserved, despite the fact that there is a large volume contraction accompanying the process: β-Co(OH)2 → Co3O4. Because of the intrinsic crystal contraction, a highly mesoporous structure with high specific surface area has been simultaneously created. The textual properties can be easily tailored by varying the annealing temperature between 200–400 °C. Interestingly, thermal re-crystallization at higher temperatures leads to the formation of a perfect 3D single-crystalline framework. Thus derived mesoporous Co3O4 nano-needles serve as a good model system for the study of lithium storage properties. The optimized sample manifests very low initial irreversible loss (21%), ultrahigh capacity, and excellent cycling performance. For example, a reversible capacity of 1079 mA h g−1 can be maintained after 50 cycles. The superior electrochemical performance and ease of synthesis may suggest their practical use in lithium-ion batteries.