NiO Nanowalls Research Articles

Thermophysical Investigation of Multiform NiO Nanowalls@carbon Foam/1-Octadecanol Composite Phase Change Materials for Thermal Management.

Multiform NiO nanowalls with a high specific surface area were constructed in situ on carbon foam (CF) to construct NiO@CF/OD composite phase change materials (CPCMs). The synthesis mechanism, microstructures, thermal management capability, and photothermal conversion of NiO@CF/OD CPCMs were systematically studied. Additionally, the collaborative enhancement effects of CF and multiform NiO nanowalls on the thermal properties of OD PCMs were also investigated. NiO@CF not only maintains the porous 3D network structure of CF, but also effectively prevents the aggregation of NiO nanosheets. The chemical structures of NiO@CF/OD CPCMs were analyzed using XRD and FTIR spectroscopy. When combined with CF and NiO nanosheets, OD has high compatibility with NiO@CF. The thermal conductivity of NiO@CF/OD-L CPCMs was 1.12 W/m·K, which is 366.7% higher than that of OD. The improvement in thermal conductivity of CPCMs was theoretically analyzed according to the Debye model. NiO@CF/OD-L CPCMs have a photothermal conversion efficiency up to 77.6%. This article provided a theoretical basis for the optimal design and performance prediction of thermal storage materials and systems.

Vertically aligned mesoporous Ce doped NiO nanowalls with multilevel gas channels for high-performance acetone gas sensors

In recent years, the potential use and development of acetone gas sensors in health monitoring and self-diagnostic applications has attracted increasing attention. Thus, accurate sensing of acetone is of crucial importance in the non-invasive diagnosis of diabetes. However, challenges remain in the detection of acetone, such as high concentrations detection limit, high operating temperature and slow response dynamics. Herein, vertically aligned Ce-doped mesoporous NiO nanowalls are prepared on Ag-Pd interdigitated electrode substrate using an in-situ growth method. The gas sensing performances show that the as-made 4 mol% Ce-doped NiO nanowalls has excellent gas response value (3.2) to 10 ppm acetone at a lower operating temperature (175 ℃) with fast adsorption and desorption equilibrium (13 s/7 s). Vertically aligned mesoporous NiO nanowalls doped by Ce element could pave the way for ultra-sensitive and low power consumption acetone gas sensors for breath gas detection.

Hierarchical NiO/TiO2 heterojuntion-based conductometric hydrogen sensor with anti-CO-interference

Constructing a heterojunction is an effective way to improve the gas sensing properties of metal oxide semiconductors. In this work, a hydrogen sensor containing hierarchical and porous NiO/TiO2 heterojunction bilayer structure was designed. The top layer is formed by the NiO nanowalls grown along the [220] direction with exposed (111) facets, and the bottom layer is formed by the [002] oriented TiO2 nanorod arrays. The exposed high energy crystal surfaces of NiO and TiO2, together with the adapted surface depletion region, induced by the formation of the heterojunction, enable the hydrogen sensor to have both a wide detection range and a much higher response to hydrogen than single layer materials. With the optimized size of the pores existing between the walls, the hydrogen sensor shows excellent prevention to interference from CO. Both the gas diffusion regulated by the porous structure and the surface interaction between H2/CO and O2- controlled by the heterojunction barrier contribute to the distinctive detection of H2 and CO at room temperature (25 ℃ ± 2 ℃).

Physical insights into alkaline overall water splitting with NiO microflowers electrodes with ultra-low amount of Pt catalyst

Electrochemical water splitting represents a promising alternative to conventional carbon-based energy sources. The hydrogen evolution reaction (HER) is a key process, still if conducted in alkaline media, its kinetics is slow thus requiring high amount of Pt based catalysts. Extensive research has been focused on reducing Pt utilization by pursuing careful electrode investigation. Here, a low-cost chemical methodology is reported to obtain large amount of microflowers made of interconnected NiO nanowalls (20 nm thick) wisely decorated with ultralow amounts of Pt nanoparticles. These decorated microflowers, dispersed onto graphene paper by drop casting, build a high performance HER electrode exhibiting an overpotential of only 66 mV at current density of 10 mA cm−2 under alkaline conditions. Intrinsic activity of catalyst was evaluated by measuring the Tafel plot (as low as 82 mV/dec) and turnover frequencies (2.07 s−1 for a Pt loading of 11.2 μg cm−2). The effect of Pt decoration has been modelled through energy band bending supported by electrochemical analyses. A full cell for alkaline electrochemical water splitting has been built, composed of Pt decorated NiO microflowers as cathode and bare NiO microflowers as anode, showing a low potential of 1.57 V to afford a current density of 10 mA cm−2 and a good long-term stability. The reported results pave the way towards an extensive utilization of Ni based nanostructures with ultralow Pt content for efficient electrochemical water splitting.

In-situ calcination of NiO nanowalls@carbon foam with hybrid 2D/3D framework to reinforce 1-octadecanol phase change materials

Well-aligned NiO nanowalls on a 3D melamine-derived carbon foam (CF) skeleton were synthesized and further employed in phase change materials (PCMs). The effect of NiO nanowalls and CF on the thermal properties of matrix 1-octadecanol (OD) PCMs was studied in detail. CF with 3D interconnected network and excellent absorption capacities was prepared by simple carbonization from commercial melamine foam (MF). NiO@CF was designed by calcining the precursor of Ni(OH)2 in-situ depositing on CF skeleton. On account of the large specific surface area of NiO nanowalls and the connected networks of CF, NiO@CF/OD composite PCMs possess high thermal storage capacity and excellent heat transfer efficiency. The thermal conductivity and specific heat capacity of NiO@CF/OD composite PCMs are 1.12 W/m·K and 2.80 J/g·K, 4.67 and 2.55 times of pure OD, respectively. The addition of NiO nanowalls and CF had a negligible influence on the phase change temperature of OD. Furthermore, the photothermal energy conversion efficiency of NiO@CF/OD composite PCMs is up to 77.6%. This research opens an avenue to superior multifunctional PCMs possessing high thermal conductivity and great specific heat capacity for low-cost and highly efficient thermal storage technologies.

A Two-Dimensional Hybrid of Nio Nanowalls and Reduced Graphene Oxide for Superior Field Emission

A Two-Dimensional Hybrid of Nio Nanowalls and Reduced Graphene Oxide for Superior Field Emission

Fabrication of Three-Dimensional Porous Materials with NiO Nanowalls for Electrocatalytic Oxygen Evolution

Nanosheets are two-dimensional (2D) nanocrystals that exhibit superior electrochemical performance. However, nanosheets are typically stacked horizontally toward the current collector, leading to poor utilization of individual nanosheets. Although most studies have fabricated three-dimensional (3D) structures using nanosheets, the wall thickness was a few hundred nanometers, suggesting that hundreds of nanosheets were restacked along the wall. In this study, we demonstrated the fabrication of a 3D structure constructed by NiO nanowalls with a thickness of 2–3 nm (3D-NiO). The specific surface area of 3D-NiO was found to be 42 m2 g–1, which is 2.6 times larger than that of NiO nanoparticles. The specific capacity of 3D-NiO was 2.5 times higher than that of NiO nanoparticles and could be attributed to the large specific surface area because of the nature of the thin nanowalls. The O2-evolution reaction (OER) activity of 3D-NiO at 1.65 V vs RHE was sixfold greater than that of NiO nanoparticles. The enhanced OER activity of 3D-NiO could be attributed to both the large specific surface area and the fabrication of diffusion paths within the 3D structure. The OER activity of 3D-NiO after 500 cycles was four times higher than that of NiO nanoparticles. Our results show that the 3D structure fabricated with thin nanowalls is a promising porous material for capacitor electrodes and electrocatalysts for applications in electrolysis and fuel cells.

Oxygen Evolution Reaction of NiO Nanowalls with a Three-Dimensional Framework

It is important to optimize the mass transport of electrons, ions and gases to enhance the catalytic activity and efficiency for electrolysis. We previously reported that nanosheets possess higher electrocatalytic activity compared to nanoparticles.1 This is attributed to the large electrochemically active surface area of nanosheets. However, nanosheets tend to re-stack, leading to poor mass transport and low efficiency. In this study, we propose a new electrocatalyst with a three-dimensional architecture composed of a framework of NiO nanowalls toward oxygen evolution reaction (OER).Macro porous carbon (MPC) was purchased from Toyo Tanso (CNovel®, Japan) and used as template. MPC was dispersed in 2-methoxyethanol, and nickel acetylacetonate was dissolved in 2-methoxyethanol. The suspension was mixed for 3 days and collected by centrifugation. The obtained powder (MPC@NiO x ) was dispersed in 2-methoxyethanol. After solvothermal treatment, the solution was centrifuged, and the dried powder was heated in air to yield macro porous NiO (3D-NiO). NiO particles were prepared without the macro porous carbon template. OER activity of the electrocatalysts was investigated using a three-electrode system consisting of a Pt mesh counter electrode and a Ag/AgCl (sat. KCl) reference electrode. 1.0 M KOH (30°C) was used as the electrolyte.TEM images of 3D-NiO showed a 3D structure constructed by 2D NiO nanowalls with very thin and smooth surface. The structure of 3D-NiO was replicated from the MPC template; MPC was oxidatively removed by calcination at 400°C. The redox peaks at a half peak potential of E 1/2 = 1.49 V vs. RHE were observed in the cyclic voltammograms for 3D-NiO and NiO particles. These redox peaks were attributed to the transformation of b-Ni(OH)2 and b-NiOOH (Ni(OH)2 « NiOOH + H+ + e-).2 The OER current at 1.8 V vs. RHE of 3D-NiO was 15 times larger than that of NiO particles. The onset potential of the OER for 3D-NiO was similar to that for NiO particles, indicating that the OER mechanism was not sensitive to the morphology of NiO. The result strongly indicates that the 3D structure with 2D nanowall is a superior design for OER electrocatalyst. Considering the diffusion path of evolved O2 molecules, the enhanced activity could also be attributed to the meso pore nature of 3D-NiO.This work was supported by Japan Society for the Promotion of Science (JSPS) Grant-in-Aid for Young Scientist (Grant Number 18K14054). References D. Takimoto, K. Fukuda, S. Miyasaka, T. Ishida, Y. Ayato, D. Mochizuki, W. Shimizu and W. Sugimoto, Electrocatalysis, 8, 144 (2017).M.-S. Kim, T.-S. Hwang and K.-B. Kim, J. Electrochem. Soc., 144, 1537 (1997).

Role of Substrate in Au Nanoparticle Decoration by Electroless Deposition.

Decoration of nanostructures is a promising way of improving performances of nanomaterials. In particular, decoration with Au nanoparticles is considerably efficient in sensing and catalysis applications. Here, the mechanism of decoration with Au nanoparticles by means of low-cost electroless deposition (ELD) is investigated on different substrates, demonstrating largely different outcomes. ELD solution with Au potassium cyanide and sodium hypophosphite, at constant temperature (80 °C) and pH (7.5), is used to decorate by immersion metal (Ni) or semiconductor (Si, NiO) substrates, as well as NiO nanowalls. All substrates were pre-treated with a hydrazine hydrate bath. Scanning electron microscopy and Rutherford backscattering spectrometry were used to quantitatively analyze the amount, shape and size of deposited Au. Au nanoparticle decoration by ELD is greatly affected by the substrates, leading to a fast film deposition onto metallic substrate, or to a slow cluster (50–200 nm sized) formation on semiconducting substrate. Size and density of resulting Au clusters strongly depend on substrate material and morphology. Au ELD is shown to proceed through a galvanic displacement on Ni substrate, and it can be modeled with a local cell mechanism widely affected by the substrate conductivity at surface. These data are presented and discussed, allowing for cheap and reproducible Au nanoparticle decoration on several substrates.

Ultrasensitive Electrochemical Impedance Detection of Mycoplasma agalactiae DNA by Low-Cost and Disposable Au-Decorated NiO Nanowall Electrodes.

Nanostructured electrodes detecting bacteria or viruses through DNA hybridization represent a promising method, which may be useful in on-field applications where PCR-based methods are very expensive, time-consuming, and require trained personnel. Indeed, electrochemical sensors combine disposability, fast response, high sensitivity, and portability. Here, a low-cost and high-surface-area electrode, based on Au-decorated NiO nanowalls, demonstrates a highly sensitive PCR-free detection of a real sample of Mycoplasma agalactiae (Ma) DNA. NiO nanowalls, synthesized by aqueous methods, thermal annealing, and Au decoration, by electroless deposition, ensure a high-surface-area platform for successful immobilization of Ma thiolated probe DNA. The morphological, chemical, and electrochemical properties of the electrode were characterized, and a reproducible detection of synthetic Ma DNA was observed and investigated by impedance measurements. Electrochemical impedance spectroscopy (EIS) ascribed the origin of impedance signal to the Ma DNA hybridization with its probe immobilized onto the electrode. The electrode successfully discriminates between DNA extracted from healthy and infected sheep milk, showing the ability to detect Ma DNA in concentrations as low as 53 ± 2 copy number μL-1. The Au-decorated NiO nanowall electrode represents a promising route toward PCR-free, disposable, rapid, and molecular detection.

Sodium dodecyl sulfate-assisted fabrication of NiO nanowalls grown on nickel foam as supercapacitor electrode materials

The NiO nanowalls which are directly grown on nickel foam (NiO NWs/NF) have been successfully synthesized via a facile sodium dodecyl sulfate-assisted hydrothermal process and subsequent annealing process. With the assistance of sodium dodecyl sulfate (SDS), ordered NiO nanowalls are formed by the NiO nanorods through a partial dissolution-redeposition process, which is proposed and verified by scan electron microscopy and high-resolution transmission electron microscopy. The addition amount of SDS highly affects both the microstructure and electrochemical performances of the NiO samples. The optimized NiO NWs/NF exhibits higher specific capacitance of 1799.8 F g−1 at 1 A g−1, excellent rate performance and superior cycle stability. The enhanced electrochemical performances benefit from the vertical growth of uniform nanowalls on the substrate, which provides open access and promotes ion/electron transport. In addition, an asymmetric supercapacitor was assembled and high energy density of 30.4 Wh kg−1 at the power density of 752.3 W kg−1 with capacitance retention of 83.7% after 5000 cycles was achieved. The results indicate that the as-prepared NiO NWs/NF material can be used as a potential binder-free electrode for supercapacitors.

High intrinsic activity of the oxygen evolution reaction in low-cost NiO nanowall electrocatalysts

NiO nanowalls grown by low-cost chemical bath deposition and thermal annealing are a high-efficiency and sustainable electrocatalytst for OER.

Correction: High intrinsic activity of the oxygen evolution reaction in low-cost NiO nanowall electrocatalysts

Correction for ‘High intrinsic activity of the oxygen evolution reaction in low-cost NiO nanowall electrocatalysts’ by Salvatore Cosentino et al., Mater. Adv., 2020, DOI: 10.1039/d0ma00467g.

Acetone sensing and modelling by low-cost NiO nanowalls

NiO nanowalls were grown by low-cost chemical bath deposition (CBD) method and thermal annealing. SEM analysis showed a high surface area and porous thin film formed by a network of ~20 nm thick and ~270 nm tall nanosheets. NiO nanowalls were prepared onto interdigitated electrodes and applied for acetone sensing. The response transients at various temperatures were recorded an successfully modelled by two adsorption sites. Both sites are active below 250 °C, while only the site with shorter response time is active above 250 °C. At the optimal temperature of 250 °C, the sensor demonstrated high sensitivity to acetone (1–40 ppm), a low limit of detection (LoD) of ~200 ppb and good selectivity. These unique features combined with the low-cost and simple fabrication process make it a cheap and efficient acetone sensor.

In Situ Growth of NiO@SnO2 Hierarchical Nanostructures for High Performance H2S Sensing.

Heterostructured metal oxides with large specific surface area are crucial for constructing gas sensors with high performance. However, using slurry-coating and screen-printing methods to fabricate gas sensors cannot result in high uniformity and reproducibility of the sensors. Here, NiO nanowalls decorated by SnO2 nanoneedles (NiO@SnO2) were in situ grown on ceramic microchips via a chemical bath deposition method to detect H2S instead of print-coating and slurry-coating methods. The morphologies and compositions of the NiO@SnO2 hierarchical nanostructures (HNSs) were well tuned by varying the growth time of the NiO@SnO2 HNSs to optimize the sensing performance. The response of the NiO@SnO2 HNSs (2 h) to 1 ppm of H2S was over 23-fold higher than that of the pure NiO nanowalls and 17-fold higher than that of the pure SnO2 nanosheets. This dramatic enhancement is attributed to the large surface area of the NiO@SnO2 HNSs and the p-n heterojunction at the heterointerface of SnO2 and NiO. The variation in the depletion layers (WSnO2 and WNiO) at the heterointerface of SnO2 and NiO greatly depends on the properties of the target gases (e.g., electron-withdrawing property (NO2) or electron-donating property (H2S)).

In situ deposited hierarchical CuO/NiO nanowall arrays film sensor with enhanced gas sensing performance to H2S

Hierarchical and heterogeneous CuO/NiO nanowall arrays were in situ grown on ceramic tubes via a facile template-free hydrothermal route, and then were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and nitrogen adsorption–desorption techniques. The resultant composites exhibit network-like CuO/NiO array structures constructed by interconnected porous nanosheets, in which the decoration of CuO nanoparticles in NiO nanowall arrays was confirmed by XRD, XPS and TEM analyses. The 2.84 at % CuO decorated NiO sensor exhibits excellent sensing properties at 133 °C. The response to 5 ppm H2S attains 36.9, which increases as high as 5.6 times compared to the NiO one. The detection limit to H2S is further decreased from 1 ppb for the pure NiO sensor to 0.5 ppb. The CuO/NiO sensor shows a wide linear range from 50 to 1000 ppb, good repeatability, selectivity and long-term stability, which is expected to be a candidate for ppb-level H2S detection in real and complex environment of industrial production. Furthermore, the dominant H2S sensing mechanism is discussed from the view of the homo- and hierarchical architecture of the CuO/NiO arrays as well as the chemical and electronic sensitization effects of CuO decoration.

Superior Li-ion storage performance of graphene decorated NiO nanowalls on Ni as anode for lithium ion batteries

Abstract Graphene decorated NiO nanowalls grown on porous Ni foam (NiO-G-Ni) are fabricated via facile electrochemical corrosion and subsequent annealing treatment. High pseudocapacitive contribution for charge storage is triggered in the NiO-G-Ni, with hierarchical porous architecture improving lithium ion diffusion and graphene backbone facilitating electron transfer. The NiO-G-Ni undergoes novel electrochemical reconstruction upon cycling, while nano-size of NiO and graphene decoration are well kept. As a result, the NiO-G-Ni exhibits superior cycle stability. It delivers initial charge/discharge capacity of 936/734 mAh g −1 at 125 mA g −1 . The charge/discharge capacity decrease little in the first few cycles and then gradually recover and maintain at 732/722 mAh g −1 after 150 cycles.

3D NiO nanowalls grown on Ni foam for highly efficient electro-oxidation of urea

3D NiO nanowalls are homogeneously grown on macroporous nickel foam by a hydrothermal method. The morphology of the NiO nanowalls are characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM) and the phase structure of NiO nanowalls is characterized by X-ray diffraction (XRD) analysis. The results indicate that the NiO nanowalls are uniformly distributed on the entire nickel foam framework. And ammonia fluoride has significant influence on the height and thickness of NiO nanowalls. With the presence of ammonia fluoride, NiO nanowalls with height of 4.6 (±0.4) μm and thickness around 50 nm were obtained, while the height and thickness decreased to 1.7 (±0.2) μm and around 20 nm without the presence of ammonia fluoride. The NiO nanowalls were used as electrodes for urea oxidation in alkaline condition. The electro-oxidation activity the catalyst is investigated by cyclic voltammetry and potential step chronoamperometry. The electrocatalytic performance of NiO electrodes depends strongly on the sample preparation condition. The 3D NiO nanowalls electrode exhibit excellent electro-oxidation activity towards urea oxidation. The morphology of the electrodes has significant influence on their activity. The current density of 3D NiO nanowalls electrode prepared with NH4F at 0.7 V reached 800 mA cm−2, which was over 4 times than that of sample prepared without NH4F. Moreover, NiO nanowalls prepared with NH4F was more stable than the one prepared without NH4F, which did not show any appreciable morphology change after being used for urea electro-oxidation for 12 h. While the one prepared without NH4F collapsed after used.

Porosity-tuned NiO nanoflakes: Effect of calcination temperature for high performing supercapacitor application

Aiming to achieve low cost energy storage applications by green technology, NiO nanoflakes have been synthesized using simple wet chemical route. Variation of calcination temperature is employed to pierce nanoholes within the nanoflakes to obtain higher effective surface area. All the samples are characterized by X-ray diffraction for phase related information. Samples are investigated via field emission scanning electron microscopy and high resolution transmission electron microscopy for morphological features whereas compositional analysis has been carried out using energy dispersive X-ray studies. Electrochemical performances of the as-prepared samples are investigated in detail to predict the potential application of this system in energy storage devices. It is observed that pore diameter and density may be enhanced with increment in calcination temperature. NiO nanowalls with the highest effective surface area (83.940 m2/g) synthesized at 900 °C exhibited a specific capacitance as high as 738 F/g (scan rate 2 mV/s) which is 82% greater than the less porous NiO sample, calcined at 500 °C (406 F/g). This high value of capacitance is correlated with nanohole dimension within nanoflakes and employing software based image analysis. This work, therefore, indicates a doorway for cost effective high performance energy storage application using morphologically modified metal oxide nanoflakes.

Enhanced photoluminescence in electrodeposited NiO nanowalls mediated by plasmonic Au nanoparticle

A comparative photoluminescence (PL) study of NiO nanowalls electrochemically deposited on indium-tin-oxide (ITO)- and gold (Au)-coated glass substrates was demonstrated. The NiO nanowalls had with an average diameter of 2–5 μm and a thickness of 50 nm. For Au-coated substrates, the nanowalls were observed to be decorated by spherical Au nanoparticles (NPs), whereas no NP was found for ITO-coated substrates. The X-ray diffraction (XRD) patterns revealed a dominant growth of NiO along (200) direction. For both the substrates, the X-ray photoelectron spectra (XPS) confirmed elemental purity of NiO with an oxidation state of +2. After eliminating the substrate effect, the nanowalls grown on Au-coated substrates revealed prominent XPS peaks related to metallic Au. Room temperature PL spectra for Au-decorated sample showed a remarkably intense peak at 544 nm corresponding to green light. The peak intensity was observed to be 30 times higher for Au-coated substrates with a wide red-shift. This optical enhancement was attributed to the far-field and near-field radiative effects caused by plasmonic resonance of Au NPs in the vicinity of high-k dielectric NiO nanowalls.