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In this work, a rational design and construction of porous spherical NiO@NiMoO4 wrapped with PPy was reported for the application of high-performance supercapacitor (SC). The results ...show that the NiMoO4 modification changes the morphology of NiO, and the hollow internal morphology combined with porous outer shell of NiO@NiMoO4 and NiO@NiMoO4@PPy hybrids shows an increased specific surface area (SSA), and then promotes the transfer of ions and electrons. The shell of NiMoO4 and PPy with high electronic conductivity decreases the charge-transfer reaction resistance of NiO, and then improves the electrochemical kinetics of NiO. At 20Ag−1, the initial capacitances of NiO, NiMoO4, NiO@NiMoO4 and NiO@NiMoO4@PPy are 456.0, 803.2, 764.4 and 941.6Fg−1, respectively. After 10,000 cycles, the corresponding capacitances are 346.8, 510.8, 641.2 and 904.8Fg−1, respectively. Especially, the initial capacitance of NiO@NiMoO4@PPy is 850.2Fg−1, and remains 655.2Fg−1 with a high retention of 77.1% at 30Ag−1 even after 30,000 cycles. The calculation result based on density function theory shows that the much stronger Mo-O bonds are crucial for stabilizing the NiO@NiMoO4 composite, resulting in a good cycling stability of these materials.
A SnO2/NiO heterostructure that is comprised of SnO2 and NiO nanoparticles was designed and demonstrated an extremely high sensing response toward formaldehyde detection. A facile one-step blending ...process with a low operating temperature of 80 °C enables an interconnected morphology for the SnO2/NiO heterostructure. Two particles were created in the morphology by encouraging the formation of crystal phases in each other, the synergetic crystal phases of the SnO2/NiO heterostructure were generated with excellent crystallinity and high crystallite size and chemically constructed. The synergetic crystalline morphology facilitates adsorbed oxygen species on the SnO2/NiO heterostructure to have effective chemical interaction with formaldehyde gas molecules in terms of not only surface and internal crystal structure but also electronic band structure. It thereby leads to an extremely high sensing response with a record value of 9121.74 in the detection of formaldehyde with a 10 ppm concentration. With the overwhelming response, the SnO2/NiO heterostructure-based sensor device showed a transient response time within 3 s, a significant stable result in repeatability including reproducibility with ca. 2% loss in the gas ON-OFF level in the 50 cycles, long-term stability for 12 days, and ultra-exclusive selectivity result. Our work suggests a realization method to develop SnO2/NiO heterostructure-based chemiresistive sensor with a superior sensing response, and thus it will be a leading research outcome in both communities of formaldehyde gas sensors and SnOx-based sensor devices.
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•A SnO2/NiO heterostructure that is comprised of SnO2 and NiO nanoparticles was designed.•Synergetic crystal phases of SnO2 and NiO nanoparticles were created in an interconnected morphology.•The synergetic crystalline morphology facilitates effective chemical interactions with formaldehyde.•The SnO2/NiO heterostructure-based sensor showed an extremely high sensing response with a 9121.74.
Abstract
The design of the earth‐abundant, nonprecious, efficient, and stable electrocatalysts for efficient hydrogen evolution reaction (HER) in alkaline media is a hot research topic in the field ...of renewable energies. A heterostructured system composed of MoS
x
deposited on NiO nanostructures (MoS
x
@NiO) as a robust catalyst for water splitting is proposed here. NiO nanosponges are applied as cocatalyst for MoS
2
in alkaline media. Both NiO and MoS
2
@NiO composites are prepared by a hydrothermal method. The NiO nanostructures exhibit sponge‐like morphology and are completely covered by the sheet‐like MoS
2
. The NiO and MoS
2
exhibit cubic and hexagonal phases, respectively. In the MoS
x
@NiO composite, the HER experiment in 1
m
KOH electrolyte results in a low overpotential (406 mV) to produce 10 mA cm
−2
current density. The Tafel slope for that case is 43 mV per decade, which is the lowest ever achieved for MoS
2
‐based electrocatalyst in alkaline media. The catalyst is highly stable for at least 13 h, with no decrease in the current density. This simple, cost‐effective, and environmentally friendly methodology can pave the way for exploitation of MoS
x
@NiO composite catalysts not only for water splitting, but also for other applications such as lithium ion batteries, and fuel cells.
•A non-thermal plasma-assisted chemical looping system is effective for H2 production.•NiO/Fe2O3 exhibits the best performance, giving high yield and selectivity for H2.•Non-thermal plasma stimulates ...the transport of lattice oxygen to the Ni sites.•Prevention of carbon deposition is key to maintain continuous H2 production.
A plasma-assisted chemical looping system for the production of H2 (PCLH) was investigated in this study. This system allows the partial oxidation of CH4 at mild temperatures (573–773 K). Four active oxygen carriers: Fe2O3, NiO-impregnated Fe2O3 (NiO/Fe2O3), SrFeO3−δ and NiO-impregnated SrFeO3−δ (NiO/SrFeO3−δ) were compared, each working both as a packed material for the plasma reactor and an oxygen source for the partial oxidation of CH4. Similar conversions of CH4, and low yields of H2 were obtained in Fe2O3 and SrFeO3−δ. It was concluded that in these cases, H2 was mainly produced from direct cracking of CH4 by plasma. In contrast, when using NiO/Fe2O3 and NiO/SrFeO3−δ, substantial production of H2 was achieved. It is proposed that there is a synergistic effect between the catalyst and the oxygen carrier; the presence of the metallic Ni phase was responsible for catalysing the production of H2, and the oxygen from the support helped prevent the build-up of coke. As a result, the activity of Ni was continuously maintained for H2 production. The chemical loop is closed with the oxygen carriers being regenerated in air with plasma and then used in the next looping cycle. The high H2 production capability in NiO/Fe2O3 was repeatable; whilst, NiO/SrFeO3−δ deactivated in the second and third cycles. Amongst the temperatures studied, NiO/Fe2O3 at 673 K resulted in the best performance for H2-rich gas production. A further increase in the operating temperature led to a total combustion of CH4.
Degradation of organic pollutants such as methylene blue (MB) from water resources is currently of particular interest. Employment of a heterojunction device with optimized layer properties and ...proper interface engineering can enhance the photocatalytic performance by taking advantage of efficient charge separation. In this work, we develop an efficient photocatalytic system for the MB degradation based on ZnO nanorod (ZnONR)/NiO core-shell heterostructure with an optimized chemical and electronic structure for achieving record MB degradation efficiency of ∼70 %. ZnONR were grown by hydrothermal technique, whereas homogeneous crystalline NiO thin films were prepared by a robust and easy for up-scaling method of ultrasonic spray pyrolysis (USP). The optimum preparation conditions of photocatalytically efficient ZnONR/NiO heterostructures imply NiO film deposition from two USP cycles at 500 °C followed by air annealing heterostructures at 600 °C. The photocatalytic performance of ZnONR/NiO core-shell structure was investigated in comparison to counterpart layers and ZnO/NiO bilayer system. Chemical composition and band alignment at the ZnONR/NiO interface were investigated by X-ray photoelectron spectroscopy, Kelvin probe and photoelectron yield spectroscopy. Current transport studies indicated the presence of built-in electric field at the n-ZnO/p-NiO heterointerface responsible for the enhanced photocatalytic activity and based on this the degradation mechanism of MB is discussed.
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A rational nanostructure design and facile synthesis method by using ZIF-67 as a template were proposed to fabricate an outstanding supercapacitor cathode. A typical ASC device delivers a remarkable ...cycling stability and potential practical application.
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•A hierarchical Co9S8@NiO composite was designed for supercapacitor.•The prepared cathode exhibits a high specific capacitance of 1627 F g−1.•A typical ASC device delivers a potential practical application.•The remarkable performance was closely related to the unique structure.
Metal-organic frameworks (MOFs) become a research hot-spot owing to their unique properties originating from the ultra-high porosity and large specific surface area with highly accessible active sites. However, the electrochemical performance of a single component is unsatisfied when MOFs are applied as electrode material in a supercapacitor. In this work, the hierarchical hollow framework involving interconnected Co9S8 structure and NiO nanosheets (Co9S8@NiO) are successfully prepared by MOFs derived methods and proposed to electrode materials. As a result, the prepared Co9S8@NiO electrode materials exhibit a superior specific capacitance of 1627 F g−1 at a current density of 1 A g−1. Moreover, an assembled hybrid supercapacitor shows a high energy density of 51.65 Wh Kg−1 at a power density of 749.8 W Kg−1 as well as excellent long-term cycling stability with 81.79% capacity retention after 10,000 cycles. Meanwhile, we concluded that the marvelous electrochemical performance is closely associated with the unique structure of NiO, in particular, the nanosheet surface provides a superior specific surface area and rich accessible redox reaction sites, thus enlarged the contact between the surface and interface of the electrode material. Finally, two supercapacitor devices connected in series can light up four light-emitting diodes (LEDs) for about 30 min. Hence, the presented strategy represents a general route for supercapacitor electrode material with promising electrochemical performance, which can combine the MOFs template and other hierarchical nanosheets together.
Microwave absorbing materials with enhanced microwave absorption performance and self-cleaning function are of great interest for military applications and human health caused by electromagnetic ...radiation pollution. Herein we report the synthesis of FeNi/NiFe2O4/NiO/C nanofibers (NFs) via electrospinning technique using nickel acetylacetonate (Ni(acac)2), ferric acetylacetonate (Fe(acac)3), and N, N-dimethylformamide (DMF)/polyacrylonitrile (PAN) solution as precursor. We also show the abilities of the materials to attenuate electromagnetic microwave and their ease of self-cleaning performance. X-ray diffraction patterns and HRTEM images reveal that the materials possess FeNi, NiFe2O4, NiO and graphite. HAADF-STEM images show that the magnetic nanoparticles distribute uniformly along the fibers. Contrast experiments had been conducted on different calcination temperatures to elucidate the impedance matching and loss mechanism. Based on the results of the experiment, excellent microwave absorption was exhibited by blending the NiFe2O4/NiO/CNFs and FeNi/NiFe2O4/NiO/CNFs into paraffin at 50 wt% and 5 wt%, respectively. Moreover, the contact angles (CA) of the as-prepared fiber films calcined at 650, 750 and 950 °C were 143°, 141° and 144°, respectively, indicating that fiber films exhibited excellent hydrophobicity and self-cleaning function. It suggested that the as-obtained NFs had an excellent application prospect in self-cleaning microwave absorbing materials.
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WS2 nanomaterials have attracted great attention in the field of electromagnetic wave absorption due to their high specific surface area, layered structure, and peculiar electronic ...properties. However, further improvements on their limited electromagnetic absorbing (EMA) capacity and bandwidth are urgently required for their practical application as EMA absorbents. In this work, WS2/NiO hybrids with heterostructures are prepared by a hydrothermal method and developed into EMA absorbents. The maximum reflection loss of the hybrids with 20% NiO loading could reach −53.31 dB at a thickness of 4.30 mm; the bandwidth with a reflection loss value of less than −10 dB is determined to be 13.46 GHz (4.54–18 GHz) when the thickness of the absorbent is between 3.5 and 5.5 mm. It is found that the enhanced EMA performance of WS2/NiO hybrids is caused by the addition of magnetic NiO, which could result in the interfaces between WS2 and NiO being responsible for the synergetic magnetic loss and dielectric loss in the hybrids. This work provides a new approach for the design of excellent EMA materials for practical applications.
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•A CeO2-P carrier rich in oxygen vacancies was synthesized for Ni-based catalyst.•High low-temperature CO2 methanation activity and excellent stability were achieved.•The role of ...oxygen vacancies in enhancing CO2 methanation performance was revealed.
Developing efficient catalysts with superior low-temperature catalytic performance is highly promising yet challenging for CO2 methanation. Here we synthesized a nanoplate-shaped CeO2, which was rich in oxygen vacancies, as the carrier to disperse the nickel nanoparticles. The resultant catalyst (Ni/CeO2-P) showed remarkable low-temperature CO2 methanation performance with a CO2 conversion of high than 84% and 100% CH4 selectivity at a low temperature of 300 °C. A 100 h-on-stream test at 300 °C demonstrated the excellent stability of Ni/CeO2-P. Even when the WHSV rose as high as 30000 mL g−1 h−1, the Ni/CeO2-P catalyst still possessed a maximum CO2 conversion of approximately 79%. The surface characterization demonstrated that the abundant oxygen vacancies on the CeO2 nanoplates led to more amounts of NiO-CeO2 structures formed, which resulted in a stronger interaction between Ni metal and CeO2 support. This stronger NiO-CeO2 interaction was proved extraordinary in promoting the reaction performance as compared with metallic Ni. Also, by the in-situ DRIFTS technology, the reaction intermediates and possible reaction pathway were raised for CO2 methanation.
•Porous NiCo2O4/NiO/Co3O4 nanoflowers (NCNs) are prepared by adding oxalic acid.•NCNs-0.1 possess optimal distribution of micro-mesopores.•NCNs-0.1 electrodes deliver an enhanced specific capacitance ...of 1693F g−1.•88% capacitance can be retained after 6000 cycles.•Excellent energy densities of 43.02 Wh kg−1 and power densities of 820.29 W kg−1.
The rational design of micro-mesopores is a hugely challenging for porous metal-based nanomaterials. Here oxalic acid (H2C2O4) as control agent is proposed for the first time to prepare 3D optimal micro-mesoporous NiCo2O4/NiO/Co3O4 nanoflowers (NCNs). Theoretical and experimental analyses demonstrate NCNs-0.1 which are prepared by adding 0.1 g H2C2O4 possess optimal distribution of micro-mesopores. The optimal structure creates abundant active sites and fluent ionic channels. Beneficially, NCNs-0.1 electrodes deliver an enhanced specific capacitance of 1693F g−1 at 1 A g−1 and outstanding cyclic stability (88% capacitance retention after 6000 cycles). Further, the assembled NCNs-0.1//AC capacitor achieves excellent energy densities of 43.02 Wh kg−1 at power densities of 820.29 W kg−1. The current NCNs-0.1 confirms a practicable method to optimize the electrochemical performances of supercapacitors by utilizing H2C2O4 to construct 3D optimal micro-mesoporous nanoflower architectures.
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