Co3O4 Nanowire Arrays Research Articles

3D integrated non-noble metal oxides nano arrays for enhanced nitrate electroreduction to ammonia

The electrochemical nitrate reduction reaction (eNO3RR) to ammonia (NH3) is a promising alternative method to the Haber-Bosch process that requires high temperature and pressure. In this contribution, the integrated Co3O4 nanowire arrays on Ni foam (Co3O4/NF) are reported to exhibit the outstanding performance with a high NH3 yield rate of 117.01 mg h−1cm−2, a superior NH3 Faradaic efficiency of 99.28 %, a high effective current density of 1475.71 mA cm−2, and a good operation durability during 40 consecutive recycling tests (40 h) in 1.0 M NaOH (0.1 M NaNO3). The high-valence metal cations as electron-deficient centers can act as Lewis-acid sites, favorably interacting with the Lewis base NO3−, and accordingly boosting the NO3− adsorption and activation. Moreover, the in-situ growth array configuration provides the substantial active sites and constructs a fast electron-transport channel, thus facilitating the conversion of NO3−-to-NH3. Density functional theory (DFT) calculations also reveal that the Co atoms as the active sites are preferred to adsorb NO3−, implying that the NO3− electroreduction dominates the cathodic reaction rather than hydrogen evolution reaction. This study provides a viable method to design integrated electrodes with enhanced eNO3RR activity and selectivity, which might have broad prospects in the application of renewable energy.

NiCu alloys anchored Co3O4 nanowire arrays as efficient hydrogen evolution electrocatalysts in alkaline and neutral media

Robust and long-lasting non-precious metal electrocatalysts are essential to achieve sustainable hydrogen production. In this work, we synthesized Co3O4@NiCu by electrodepositing NiCu nanoclusters onto Co3O4 nanowire arrays that were formed in situ on nickel foam. The introduction of NiCu nanoclusters altered the inherent electronic structure of Co3O4, significantly increasing the exposure of active sites and enhancing endogenous electrocatalytic activity. Co3O4@NiCu exhibited overpotentials of only 20 and 73 mV, respectively, at 10 mA cm−2 current densities in alkaline and neutral media. These values were equivalent to those of commercial Pt catalysts. Finally, the electron accumulation effect at the Co3O4@NiCu, along with a negative shift in the d-band center, is finally revealed by theoretical calculations. Hydrogen adsorption on consequent electron-rich Cu sites was effectively weakened, leading to a robust catalytic activity for the hydrogen evolution reaction (HER). Overall, this study proposes a practical strategy for creating efficient HER electrocatalysts in both alkaline and neutral media.

CoO (1 1 1) nanowire arrays for High-efficiency electrochemical nitrate reduction to ammonia

Efficient and robust catalysts are significant for electrochemical nitrate reduction to value-added ammonia (NH3). Here, we propose CoO (111) nanowire array on titanium mesh (CoO NWA/TM) as a high-efficiency electrocatalyst for NO3− conversion to NH3. This catalyst reaches a remarkable NH3 yield of 6.8 mg h−1 cm−2 and a high Faradaic efficiency of 95.1%, which also shows excellent electrochemical durability. The catalytic mechanism of CoO NWA/TM is revealed by theoretical calculations.

Construction of 3D Hierarchical Co3O4@CoFe-LDH Heterostructures with Effective Interfacial Charge Redistribution for Rechargeable Liquid/Solid Zn-Air Batteries.

Constructing three-dimensional (3D) hierarchical heterostructures is an appealing but challenging strategy to improve the performance of catalysts for electrical energy devices. Here, an efficient and robust flexible self-supporting catalyst, interface coupling of ultrathin CoFe-LDH nanosheets and Co3O4 nanowire arrays on the carbon cloth (CC/Co3O4@CoFe-LDH), was proposed for boosting oxygen evolution reaction (OER) in rechargeable liquid/solid Zn-air batteries (ZABs). The strong interfacial interaction between the CoFe-LDH and Co3O4 heterostructures stimulated the charge redistribution in their coupling regions, which improved the electron conductivity and optimized the adsorption free energy of OER intermediates, ultimately boosting the intrinsic OER performance. Besides, the 3D hierarchical nanoarray structure facilitated the exposure of catalytically active centers and rapid electron/mass transfer during the OER process. As such, the CC/Co3O4@CoFe-LDH catalyst achieved excellent OER catalytic activity in alkaline medium, with a small overpotential of 237 mV at 10 mA cm-2, a low Tafel slope of 35.43 mV dec-1, and long-term durability of up to 48 h, significantly outperforming the commercial RuO2 catalyst. More impressively, the liquid and flexible solid-state ZABs assembled by the CC/Co3O4@CoFe-LDH hybrid catalyst as the OER catalyst presented a stable open circuit voltage, large power density, superb cycling life, and satisfactory flexibility, indicating great potential applications in energy technology. This work provides a good guidance for the development of advanced electrocatalysts with heterostructures and an in-depth understanding of electronic modulation at the heterogeneous interface.

In-situ oriented Sc-Co3O4 nanowire arrays for highly efficient ethanol detection

Improving the response of gas sensors has always been a hot research topic. Due to their unique electronic energy level structure, the compositing rare-earth (RE) element materials display unique properties in many fields such as catalysis, luminescence, and energy conversion. Along these lines, combining materials with the RE element of scandium (Sc) is considered a new method to optimize the performance of sensors based on the employment of ZIF-67 derived Co3O4 nanowire arrays. In this work, the Sc element was uniformly distributed on the surface of the Co3O4 nanowires, which were grown by enforcing hydrothermal and chemical bath-based methods. Based on the 30 % Sc composite Co3O4 nanowire array, the sensors show a maximum response of 32–100 ppm ethanol at a lower operating temperature (110 °C). The variation of the response was small range even after 35 days. Interestingly, the extracted response has increased more than three times that of the pure Co3O4 nanowire array devices. In addition, we tested the ethanol concentration range of 10–500 ppm and showed good performance. The gas-sensing properties of the sensors were systematically tested towards volatile organic compounds, including ethanol, acetone, methanol, etc. Based on the 30 % Sc composite Co3O4 nanowire array, the sensors still exhibit excellent selectivity to ethanol. The enhanced sensing performance is attributed to the strong catalytic effect of Sc and the modification of the surface morphology of Co3O4 by Sc. Our work provides an effective and promising method for improving the ethanol sensing performance of the ZIF-67 derived Co3O4 nanowires at low-temperature values.

Electroreduction of Nitrate to Ammonia on Palladium-Cobalt-Oxygen Nanowire Arrays.

Developing high-efficiency electrocatalysts for the selective reduction of nitrate to valuable ammonia is of great significance. Herein, Pd-PdO-modified Co3O4 nanowire arrays on nickel foam (PdCoO/NF) are fabricated by a facile cation-exchange reaction. Pd and PdO can facilitate the generation of adsorbed hydrogen, and abundant oxygen vacancies can promote nitrate activation. Therefore, the PdCoO/NF exhibits a superior nitrate conversion rate (89.3%), Faradaic efficiency (88.6%), and ammonium selectivity (95.3%) at -1.3 V versus a saturated calomel electrode. The source of the produced ammonia is confirmed by 15N isotope labeling experiments and 1H magnetic resonance. This presented synthetic method provides a powerful strategy for the preparation of nanowire arrays with controllable compositions for selective nitrate electroreduction to ammonia.

Hetero-epitaxy growth of cobalt oxide/nickel oxide nanowire arrays on alumina substrates for enhanced ethanol sensing characteristics

In this work, Co3O4 nanowire arrays are prepared in-situ on the flat alumina substrates via a simple hetero-epitaxial growth without adding seed layers. It is found that the density of Co3O4 nanowires can be regulated by varying the concentration of NH4F that acts as substrate activation promoting the formation of nuclei on alumina substrate. In order to improve the gas-sensing performance, porous NiO nanosheets are anchored on the surface of Co3O4 nanowire arrays to form a novel heterostructure (Co3O4/NiO). Gas-sensing tests indicate a higher response value of these array composites towards ethanol (Rg/Ra = 4.26) than that of pristine Co3O4 nanowire arrays (Rg/Ra = 1.27) and NiO nanosheets (Rg/Ra = 1.89). The improved gas-sensing performances resulting from the special array structures and novel heterojunctions can provide abundant diffusion channels for gas molecules as well as a synergistic effect between Co3O4 and NiO.

Electroporation-coupled electrochemical oxidation for rapid and efficient water disinfection with Co3O4 nanowire arrays-modified graphite felt electrodes

Biologically unsafe drinking water occurs in developing regions lack of centralized water treatment plants. Herein, Co3O4 nanowire electrodes with Co3O4 nanowire arrays grown on graphite felt were fabricated and employed to construct a flow-through electrode system (FES) for rapid and efficient water disinfection, which achieved over 6.7-log E. coli removal under applied voltage of 2.5 V and flow rate of 65 mL/min (HRT ∼ 4.5 s) with energy consumption of 2.3 Wh/m3. The FES also achieved over 6.7-log removal at 2.5 V for the Gram-negative P. aeruginosa under ∼ 60 mL/min and for Gram-positive bacteria (E. faecalis and S. aureus) under ∼ 40 mL/min, and the Gram-negative bacteria were more vulnerable to FES disinfection than Gram-positive ones due to their larger sizes and thinner cell walls. In-situ sampling and live/dead backlight staining experiments revealed that pathogen inactivation mainly occurred on anode via the sequential adsorption, inactivation and desorption processes under the mass transfer forces of electric field attraction and flow scouring effect in porous electrodes. The disinfection mechanisms on the Co3O4 nanowire anode were recognized to be electroporation and electrochemical oxidation, and the pores generated by electroporation can provide diffusion channels for reactive species into the pathogen cells, promoting the disinfection performance.

Tuning the Electronic Structure of CoO Nanowire Arrays by N-Doping for Efficient Hydrogen Evolution in Alkaline Solutions

Electrochemical hydrogen evolution reactions (HER) have drawn tremendous interest for the scalable and sustainable conversion of renewable electricity to clear hydrogen fuel. However, the sluggish kinetics of the water dissociation step severely restricts the high production of hydrogen in alkaline media. Tuning the electronic structure by doping is an effective method to boost water dissociation in alkaline solutions. In this study, N-doped CoO nanowire arrays (N-CoO) were designed and prepared using a simple method. X-ray diffraction (XRD), element mappings and X-ray photoelectron spectroscopy (XPS) demonstrated that N was successfully incorporated into the lattice of CoO. The XPS of Co 2p and O 1s suggested that the electronic structure of CoO was obviously modulated after the incorporation of N, which improved the adsorption and activation of water molecules. The energy barriers obtained from the Arrhenius relationship of the current density at different temperatures indicated that the N-CoO nanowire arrays accelerated the water dissociation in the HER process. As a result, the N-CoO nanowire arrays showed an excellent performance of HER in alkaline condition. At a current density of 10 mA cm−1, the N-CoO nanowire arrays needed only a 123 mV potential, which was much lower than that of CoO (285 mV). This simple design strategy provides some new inspiration to promote water dissociation for HER in alkaline solutions at the atomic level.

Synergistic metal-oxide interaction for efficient self-reconstruction of cobalt oxide as highly active water oxidation electrocatalyst

Developing catalysts with outstanding performance for oxygen evolution reaction (OER) is crucial to advance energy conversion technologies. In these regards, catalysts based on 3d transition metals have recently attracted much attention, yet further development is required. Here, we present a new type of heterostructure catalyst in which CoO nanowire arrays are hybridized with tungsten nanoparticles (W-CoO), and are self-supported on conductive carbon cloth (CC). Electronic coupling effects at the W-CoO heterointerface promote electron transfer and OER kinetics to expedite the formation of oxyhydroxide species, which are the active sites for OER processes. A variety of in situ and ex situ characterization methods are employed to reveal deep insights into surface transformations and investigate the relationship between the conversion to oxyhydroxide moieties and OER performance. This report presents new understanding of the rational design and synthesis of catalysts that exhibit outstanding performance as electrochemical water splitting electrode for OER.

Oxygen vacancy-enriched Co3O4 as lithiophilic medium for ultra-stable anode of lithium metal batteries

Lithium metal as a promising anode material has been widely applied in many advanced high-energy density batteries. However, uncontrollable Li dendrite formation and infinite volume expansion in lithium anode result in short lifespan and severe safety hazards. In this contribution, we report that utilization of oxygen vacancy-enriched Co3O4 nanowire arrays as lithiophilic material is an effective strategy to obtain ultra-long stable lithium metal anode. The oxygen vacancy can serve as electronic charge carrier to facilitate electron transfer. Moreover, it can induce the generation of local electric field to accelerate lithium ions migration and enable uniform Li+ distribution, which are beneficial for homogeneous lithium nucleation. Combining the excellent ionic/electronic diffusion and the volume buffer offered by the nanowire arrays, the obtained electrode shows high coulombic efficiency of 98.5% at 1 mA cm−2 for 230 cycles.

An enhancement on supercapacitor properties of porous CoO nanowire arrays by microwave-assisted regulation of the precursor

A microwave-assisted hydrothermal approach with a follow up thermal treatment was employed to prepare 1D porous CoO nanowires, which is constructed by numerous high crystallinity nanoparticles. A significant change in crystal structure of the precursor were observed, as position shift and absence of some diffraction peaks, which was induced by the microwave-assistance during hydrothermal process. Moreover, the precursor’s purity was also effectively improved. As a result, the as-synthesized CoO annealed from the microwave-assisted precursor exhibited a morphology and phase structure significantly different from that of without microwave involvement. Benefiting from the ‘microwave effect’, the microwave-assisted as-fabricated porous CoO nanowires showed an enhanced specific capacitance (728.8 versus 503.7 F g−1 at 1 A g−1 ), strengthened rate performance (70.0% versus 53.2% maintenance at 15 A g−1), reduced charge transfer resistance (1.06 Ω versus 2.39 Ω), enlarged window voltage (0.85 versus 0.7 V) and enhanced cycle performance (82.3% versus 76.5% retention after 5000 cycles at 15 A g−1), compared with that of sample without microwave assistance. In addition, the corresponding electrochemical properties are also higher than those reported CoO sample prepared by solvothermal method. In conclusion, this work provides a practical way for enhancing electrochemical properties of supercapacitor materials through adjusting the precursor by microwave assistance into hydrothermal process.

Pore engineering of Co3O4 nanowire arrays by MOF-assisted construction for enhanced acetone sensing performances

Array-based sensors have been regarded as excellent candidates for the gas-sensing elements owing to their low-cost preparation, great miniaturization potential as well as stable performance. However, it still remains a great challenge to prepare porous arrays and regulate their porosity to increase pores for gas transport and active sites for surface reactions. To solve this problem, the porosity of metal oxide arrays (Co3O4) that had grown directly in-situ on the surface of ceramic substrates was regulated by the constructing and oxidizing of MOFs (ZIF-67) that coated on the surface cobalt-containing precursor arrays. It was found that the porosity and surface area of Co3O4 nanowire arrays increased with the content of ZIF-67. The porous Co3O arrays with the highest porosity and surface area exhibited the highest response value (Rg/Ra = 16.7), the lowest optimal operating temperature (200 °C) as well as the fastest response/recovery time (4/39 s) towards acetone. These porous Co3O4 arrays are thus promising gas-sensing materials for acetone detection with excellent performances. This novel strategy to enhance the porosity of arrays can pave a new way to improve the gas-sensing properties of array film-based sensors.

Boosting Zn-ion storage capability of self-standing Zn-doped Co3O4 nanowire array as advanced cathodes for high-performance wearable aqueous rechargeable Co//Zn batteries

Neutral aqueous rechargeable Co3O4//Zn batteries with high-output voltage and outstanding cycling stability have yielded new insights into wearable energy-storage devices. To meet the increasing demand for a means of powering wearable and portable devices, the development of a high-performance fiber-shaped Co//Zn battery would be highly desirable. However, the intrinsically poor conductivity of Co3O4 significantly restricts the application of these high-capacity and high-rate aqueous rechargeable battery. Encouragingly, density functional theory (DFT) calculations demonstrate that the substitution of Zn for Co3+ leads to an insulator-metal transition in the Zn-doped Co3O4 (Zn-Co3O4). In this study, we used metallic Zn-Co3O4 nanowire arrays (NWAs) as a novel binder-free cathode to successfully fabricate an all-solid-state fiber-shaped aqueous rechargeable (AFAR) Co//Zn battery. The resulting fiber-shaped Co//Zn battery takes advantage of the enhanced conductivity, increased capacity, and improved rate capability of Zn-Co3O4 NWAs to yield a remarkable capacity of 1.25 mAh·cm−2 at a current density of 0.5 mA·cm−2, extraordinary rate capability (60.8% capacity retention at a high current density of 20 mA·cm−2) and an admirable energy density of 772.6 mWh·cm−3. Thus, the successful construction of Zn-Co3O4 NWAs provides valuable insights into the design of high-capacity and high-rate cathode materials for aqueous rechargeable high-voltage batteries.

Coordinating Adsorption and Catalytic Activity of Polysulfide on Hierarchical Integrated Electrodes for High-Performance Flexible Li-S Batteries.

Lithium-sulfur (Li-S) batteries have been known to be a promising substitute because of their much higher theoretical energy density than that of traditional Li-ion batteries. However, the low utilization of sulfur caused by the poor conductivity of sulfur and shuttle of lithium polysulfides (LiPSs) severely restrict the commercial application of Li-S batteries, especially in flexible wearable devices. Herein, a hierarchical nitrogen-doped carbon nanotube (NCNT)@Co-Co3O4 nanowire array (NWA)-integrated electrode was developed based on the rational design of density functional theory calculations, which shows simultaneous confinement adsorption and catalysis conversion of LiPSs. In situ Raman spectra further proved that the NCNT@Co-Co3O4 NWAs exhibit sufficient adsorption capacity and high catalytic conversion of LiPSs. As a result, the NCNT@Co-Co3O4@S electrode exhibited the desirable specific capacity and excellent cyclic stability at both low and high sulfur loadings. Moreover, pouch cells with the NCNT@Co-Co3O4@S cathode show higher capacity under flat or bending states and longer cycle stability than that of the reported results. This work provides a new approach for the development of high-performance Li-S batteries toward future wearable electronics.

In situ electrochemical conversion of cobalt oxide@MOF-74 core-shell structure as an efficient and robust electrocatalyst for water oxidation

In recent years, applications of metal-organic frameworks (MOFs) in electrocatalysis, including hydrogen and oxygen evolution reactions, have attracted increasing attention for renewable energy conversion. Herein, the fabrication of core-shell structured Co3O4@MOF-74 catalysts is proposed and realized with the tunable thickness of MOF shell layers, where Co3O4 nanowire arrays prefabricated on Ni foam are employed as the template as well as the metal source to react with organic ligands to achieve the MOF layers. Importantly, the optimized Co3O4@MOF-74 structures exhibit much enhanced catalytic activities towards oxygen evolution reaction (OER), requiring an impressively low overpotential of 285 mV to afford a current density of 50 mA cm−2 together with a small Tafel slope of 43 mV/dec, as compared with the pristine Co3O4 sample. By investigating the Co3O4@MOF-74 structure after OER stability test, the conversion of MOF-74 into cobalt hydroxide shell layers is thoroughly characterized and confirmed, suggesting the in situ electrochemical conversion of MOF structures during the electrochemical process. All these results do not only uncover the changes in crystalline and chemical structures of MOFs for electrocatalytic reactions, but also help to comprehend and design novel MOFs as efficient and robust electrocatalysts for practical utilization.

Corrigendum to “N-doped CoO nanowire arrays as efficient electrocatalysts for oxygen evolution reaction” 37 (2019) 13–17

Corrigendum to “N-doped CoO nanowire arrays as efficient electrocatalysts for oxygen evolution reaction” 37 (2019) 13–17

WITHDRAWN: Corrigendum to “N-doped CoO nanowire arrays as efficient electrocatalysts for oxygen evolution reaction” [J. Energy Chem. 37 (2019) 13–17

This article has been withdrawn at the request of the editor. The Publisher apologizes for any inconvenience this may cause. The full Elsevier Policy on Article Withdrawal can be found at https://www.elsevier.com/about/our-business/policies/article-withdrawal .

Hierarchical CoO@Ni(OH)2 core–shell heterostructure arrays for advanced asymmetric supercapacitors

Constructing multicomponent electrode materials with a rational structure is an effective route to develop high-performance supercapacitors. We herein report a novel nickel-foam-supported hierarchical CoO@Ni(OH)2 nanowire-nanosheet core–shell heterostructure array synthesized by a facile hydrothermal-electrodeposition strategy. The core CoO nanowire arrays with good electrical conductivity and shell Ni(OH)2 nanosheets with thickness of ∼ 2 nm synergistically contributes to increased active sites, fast mass transfer, and improved structural stability. Consequently, the optimal CoO@Ni(OH)2–400 s architecture delivers a high specific capacitance of 1418.2 F g−1 at 1 A g−1 and 93.7% retention after 5000 cycles. Furthermore, the CoO@Ni(OH)2//activated carbon asymmetric supercapacitor could achieve an outstanding energy density of up to 92.47 W h kg−1 at 800 W kg−1. This simple but effective strategy provides insight into the development of core–shell hierarchical architectures for constructing high-performance supercapacitors.

Density-dependent of gas-sensing properties of Co3O4 nanowire arrays

Abstract Well-oriented Co3O4 nanowire arrays were synthesized in-situ on Al2O3 substrates via a simple hydrothermal method without seed layers. The phase structure and array morphology of Co3O4 nanowire arrays were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It was revealed that the array density of Co3O4 nanowire arrays could be controlled by the concentration of ammonium fluoride. The gas-sensing measurement revealed that the array structure on the surface of gas sensors exerted great impact on their performances. It was found the response value enhanced and then decayed with the increased array density of Co3O4 nanowires. We concluded that the Co3O4 nanowire arrays with moderate array density can possess highly exposed effective surface area to provide more pathways for gas diffusion than other samples. Our studies can provide a significant guidance on array design to fabricate high performance gas sensors. Moreover, the as-designed Co3O4 nanowire arrays have potential application in trimethylamine (TEA) detection.