Metal-oxide Array Research Articles

Investigation of Chemiresisitive Electronic Nose for the Analysis of Multiple Analytes Using Pattern Recognition Algorithm

The multiple analytes produced during the operation of nuclear facilities are required to monitor the smooth operation of the plant in the environment of high temperature and radioactivity in real time. A chemiresisitive electronic nose was investigated and developed to analyze the multiple analytes generated in the nuclear reactor/allied facilities. An electronic nose consists of chemiresisitive sensor, array, housing, hardware, software, and pattern recognition algorithm. The sensor and array of different semiconductor metal oxides were prepared, processed, and developed to sense the multiple analytes. The hardware and data acquisition software (DAS) was designed and developed to acquire the dynamic responses from the array of four sensors. The hardware provides a low excitation voltage for measurement of the dynamic response of four sensors towards the improvement of the life of the sensor. The various experiments were conducted with multiple analytes at different temperatures to study the analysis of analytes. The performance of the hardware and DAS were tested and evaluated with the sensor array responses towards three analytes, viz., hydrogen (H2), formaldehyde (HCHO), and hydrazine (NH2NH2). Different features evaluated from the response traces were processed to teach the instrument using pattern recognition algorithms. The training and real-time testing of the sensor array realized the qualitative discrimination and quantitative estimation of the analytes.

Fabrication of metal-oxide arrays: mechanism of solvent-mediated metal infiltration into block copolymer nanopatterns

Fabrication of metal-oxide arrays: mechanism of solvent-mediated metal infiltration into block copolymer nanopatterns

Morphology Engineering of the Asymmetric PS-b-P4VP Block Copolymer: From Porous to Nanodot Oxide Structures.

In the present work, we demonstrate the formation of oxide porous and nanodot structures from the same block copolymer (BCP) by the phase inversion of a BCP template. We investigated the effect of solvent annealing time on the ordering of asymmetric, cylinder forming, polystyrene-b-poly(4-vinylpyridine) (PS-b-P4VP) BCP. Phase separation of PS-b-P4VP was achieved by solvent vapor annealing (SVA) in a solvent atmosphere that is (partially) selective to P4VP to initially generate hexagonally arranged, cylindrical arrays of the expected structure. The morphology of the BCP changed from P4VP hexagonally packed cylinders to an 'inverse' structure with PS cylinders embedded in a P4VP matrix. This suggests that selective swelling occurs over time such that the swollen P4VP phase becomes the majority volume component. Metal ions (Ga3+, In3+) were infiltrated into the BCP templates by a solution-mediated infiltration approach, followed by an ultraviolet-ozone treatment to remove the polymer and oxidize the metallic ions to their oxides. The findings show that a single BCP can be used to create both metal oxide arrays and porous structures of metal oxides by simply varying the duration of the solvent annealing process. The resulting structures were analyzed through several methods including scanning electron microscopy, atomic force microscopy, X-ray photoelectron spectroscopy (XPS), transmission electron microscopy, and energy-dispersive X-ray spectroscopy. XPS analyses confirmed the complete elimination of the BCP template and the presence of metal oxides. This study provides important insights into the development of functional BCP materials with inverse structures.

Ionic liquid–controlled growth of bifunctional NiCo2O4 nanostructures with different dimensionalities on carbon cloth for oxygen evolution reaction and asymmetric supercapacitor

The design structure of electrocatalysts/electrode materials is important for achieving highly efficient energy conversion and storage in electrochemical energy devices. We report the synthesis of 3D NiCo2O4 hierarchical nanocactus arrays (NiCo2O4–NC) comprising 1D nanowires and 2D nanoflakes on carbon cloth by controlling the concentration of ionic liquid (IL) 1–dodecyl–3–methylimidazolium acetate ([C12MIm]Ac). For both oxygen evolution reaction (OER) and asymmetric supercapacitors (ASC), NiCo2O4–NC shows enhanced electrochemical performance. Impressively, for the OER process, NiCo2O4–NC exhibits an overpotential of 294 mV at 10 mA cm−2, Tafel slope of 77 mV dec−1, and superior stability. As a supercapacitor electrode, NiCo2O4–NC exhibits a high specific capacitance of 1842 F g−1 at 1 A g−1, outstanding rate capability, and superior cycling stability. Moreover, NiCo2O4–NC–based ASC produces a high energy density of 46.1 Wh kg−1 at power density of 557.4 W kg−1. The outstanding electrochemical performance is attributed to the distinct structure of NiCo2O4–NC with the merits of both 1D nanowires and 2D nanoflakes. This work not only offers an effective mean to design nanostructured metal oxide arrays with improved electrochemical performance but also lays the foundation of studying the application potential of ILs in the synthesis of multifunctional materials.

Quest for quantum states via field-altering technology

We report quantum phenomena in spin-orbit-coupled single crystals that are synthesized using an innovative technology that “field-alters” crystal structures via application of magnetic field during crystal growth. This study addresses a major challenge facing the research community today: A great deal of theoretical work predicting exotic states for strongly spin-orbit-coupled, correlated materials has thus far met very limited experimental confirmation. These conspicuous discrepancies are due in part to the extreme sensitivity of these materials to structural distortions. The results presented here demonstrate that the field-altered materials not only are much less distorted but also exhibit phenomena absent in their non-altered counterparts. The field-altered materials include an array of 4d and 5d transition metal oxides, and three representative materials presented here are Ba4Ir3O10, Ca2RuO4, and Sr2IrO4. This study provides an approach for discovery of quantum states and materials otherwise unavailable.

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.

Cover Feature: Hierarchical Transition Metal Oxide Arrays Grown on Graphene‐Based Fibers with Enhanced Interface by Thin Layer of Carbon toward Solid‐State Asymmetric Supercapacitors (ChemElectroChem 8/2020)

Cover Feature: Hierarchical Transition Metal Oxide Arrays Grown on Graphene‐Based Fibers with Enhanced Interface by Thin Layer of Carbon toward Solid‐State Asymmetric Supercapacitors (ChemElectroChem 8/2020)

Hierarchical Transition Metal Oxide Arrays Grown on Graphene‐Based Fibers with Enhanced Interface by Thin Layer of Carbon toward Solid‐State Asymmetric Supercapacitors

AbstractCarbon‐based asymmetric supercapacitors with high performance hold broad application prospects in wearable devices. Forming a smooth interface between the active transition metal oxides and carbon substrate for providing electron‐transfer channels and accommodating the volume contraction for hybrid electrodes is a key issue to be tackled. Herein, both fibrous cathode and anode are designed on the basis of conductive graphene/carbon nanotube hybrid fibers by introducing pseudocapacitive NiCo2O4 nano‐grass arrays or forming interconnected pores, respectively. For hierarchical positive fibers, a nitrogen‐doped carbon (NC) middle layer is employed to effectively regulate the electronic structural states between NiCo2O4 and fiber substrate. The cycling and rate performance of cathode are significantly improved due to the strong interfacial bonding and abundant electrochemical active sites. Moreover, an interconnected porous structure is also developed to provide both unlimited axial and radial channels to promote electrolyte ion diffusion sufficiently in the porous negative electrode. The assembled solid‐state flexible asymmetric supercapacitor delivers a high energy density of 11.2 μWh cm−2 with a power density of 472.1 μW cm−2, as well as an excellent long cycling performance with 93 % capacitance retention after 10000 cycles.

Hierarchical Nanosheet Arrays of Metal Oxides Guide Uniform Deposition for Lithium Anodes

Lithium metal, regarded as the “Holy Grail” of lithium battery anodes, has been considered as the most promising material for high-energy density rechargeable batteries. However, its practical application has been hindered by the uncontrolled dendrite growth of the lithium metal during charge–discharge cycles. Guiding uniform deposition of lithium during cycling is an effective route to solve the problem. In this contribution, nanosheet arrays of lithiophilic metal oxides with a hierarchical structure, that is, primary vertical thin arrays coupled with secondary grid-like ones, were constructed on a Cu current collector to regulate lithium nucleation and growth. It was found that the primary vertical thin nanosheet arrays could reduce the current density and provide adequate lithiophilic sites with a lower nucleation barrier, while the secondary grid-like nanosheet arrays offered facile Li-ion diffusion and a large volume for lithium deposition. Owing to the uniform deposition behavior and stable electrod...

A Mini-System Integrated with Metal-Oxide-Semiconductor Sensor and Micro-Packed Gas Chromatographic Column.

In this work, a mini monitoring system integrated with a microfabricated metal oxide array sensor and a micro packed gas chromatographic (GC) column was developed for monitoring environmental gases. The microfabricated packed GC column with a 1.6 m length was used to separate the environmental gas, and the metal oxide semiconductor (MOS) array sensor, fabricated with nano-sized SnO-SnO2 sensitive materials, was able to effectively detect each component separated by GC column. The results demonstrate that the monitoring system can detect environmental gas with high precision.

Nanoflake Arrays of Lithiophilic Metal Oxides for the Ultra‐Stable Anodes of Lithium‐Metal Batteries

AbstractA molten lithium infusion strategy has been proposed to prepare stable Li‐metal anodes to overcome the serious issues associated with dendrite formation and infinite volume change during cycling of lithium‐metal batteries. Stable host materials with superior wettability of molten Li are the prerequisite. Here, it is demonstrated that a series of strong oxidizing metal oxides, including MnO2, Co3O4, and SnO2, show superior lithiophilicity due to their high chemical reactivity with Li. Composite lithium‐metal anodes fabricated via melt infusion of lithium into graphene foams decorated by these metal oxide nanoflake arrays successfully control the formation and growth of Li dendrites and alleviate volume change during cycling. A resulting Li‐Mn/graphene composite anode demonstrates a super‐long and stable lifetime for repeated Li plating/stripping of 800 cycles at 1 mA cm−2 without voltage fluctuation, which is eight times longer than the normal lifespan of a bare Li foil under the same conditions. Furthermore, excellent rate capability and cyclability are realized in full‐cell batteries with Li‐Mn/graphene composite anodes and LiCoO2 cathodes. These results show a major advancement in developing a stable Li anode for lithium‐metal batteries.

Microfabricated metal oxide array sensor based on nanosized SnO–SnO2 sensitive material

In this work, a microfabricated metal oxide (MOX) array sensor based on nanosized SnO–SnO2 sensitive material was proposed. To maximize detection response and reduce power consumption, sensitive units supported by a multi-layer beam were suspended in center of micro reaction cell which could greatly improve thermal isolation. The sensitive units were fabricated with nanosized SnO–SnO2 sensitive material, and Au-doped sensitive material was proposed which was able to greatly increase selectivity and sensitivity of sensitive film. The results demonstrate that the sensitive unit has good specificity of benzene, and the MOX array sensor was able to detect benzene with an extremely low concentration, in which the lowest detectable concentration was less than 5 ppb.

Rational Design of Metal‐Organic Framework Derived Hollow NiCo2O4 Arrays for Flexible Supercapacitor and Electrocatalysis

Metal‐organic frameworks (MOFs) are promising porous precursors for the construction of various functional materials for high‐performance electrochemical energy storage and conversion. Herein, a facile two‐step solution method to rational design of a novel electrode of hollow NiCo2O4 nanowall arrays on flexible carbon cloth substrate is reported. Uniform 2D cobalt‐based wall‐like MOFs are first synthesized via a solution reaction, and then the 2D solid nanowall arrays are converted into hollow and porous NiCo2O4 nanostructures through an ion‐exchange and etching process with an additional annealing treatment. The as‐obtained NiCo2O4 nanostructure arrays can provide rich reaction sites and short ion diffusion path. When evaluated as a flexible electrode material for supercapacitor, the as‐fabricated NiCo2O4 nanowall electrode shows remarkable electrochemical performance with excellent rate capability and long cycle life. In addition, the hollow NiCo2O4 nanowall electrode exhibits promising electrocatalytic activity for oxygen evolution reaction. This work provides an example of rational design of hollow nanostructured metal oxide arrays with high electrochemical performance and mechanical flexibility, holding great potential for future flexible multifunctional electronic devices.

Generic Synthesis of Carbon Nanotube Branches on Metal Oxide Arrays Exhibiting Stable High-Rate and Long-Cycle Sodium-Ion Storage.

A new and generic strategy to construct interwoven carbon nanotube (CNT) branches on various metal oxide nanostructure arrays (exemplified by V2 O3 nanoflakes, Co3 O4 nanowires, Co3 O4 -CoTiO3 composite nanotubes, and ZnO microrods), in order to enhance their electrochemical performance, is demonstrated for the first time. In the second part, the V2 O3 /CNTs core/branch composite arrays as the host for Na(+) storage are investigated in detail. This V2 O3 /CNTs hybrid electrode achieves a reversible charge storage capacity of 612 mAh g(-1) at 0.1 A g(-1) and outstanding high-rate cycling stability (a capacity retention of 100% after 6000 cycles at 2 A g(-1) , and 70% after 10 000 cycles at 10 A g(-1) ). Kinetics analysis reveals that the Na(+) storage is a pseudocapacitive dominating process and the CNTs improve the levels of pseudocapacitive energy by providing a conductive network.

Controllable synthesis of hierarchical porous nickel oxide sheets arrays as anode for high-performance lithium ion batteries

Customized hierarchical porous metal oxide arrays is of great importance for construction of high-performance electrochemical devices. In this work, we report hierarchical porous (HP)-NiO sheets arrays by a facile hydrothermal method. Interestingly, the obtained NiO sheets arrays show HP systems, and are composed of cat-ear-like sheets main structure and interconnected nanosheets secondary structure. Moreover, the secondary nanosheets are highly porous and consist of cross-linked nanoparticles of 30–100nm. The electrochemical performances of the HP-NiO sheets arrays are evaluated as anode for Li ion batteries. Compared with the normal NiO sheets arrays, enhanced electrochemical performances are achieved for the HP-NiO sheets, including higher capacity, better cycling life and high-rate capability. The HP-NiO sheets can deliver a specific capacity of 511mAhg−1 at 3Ag−1, higher than the normal NiO sheets arrays (374mAhg−1 at 3Ag−1), due to the hierarchical porous array configuration with large surface area, fast ion diffusion path and better accommodation of volume change.

Controllable Synthesis of Copper Oxide/Carbon Core/Shell Nanowire Arrays and Their Application for Electrochemical Energy Storage.

Rational design/fabrication of integrated porous metal oxide arrays is critical for the construction of advanced electrochemical devices. Herein, we report self-supported CuO/C core/shell nanowire arrays prepared by the combination of electro-deposition and chemical vapor deposition methods. CuO/C nanowires with diameters of ~400 nm grow quasi-vertically to the substrates forming three-dimensional arrays architecture. A thin carbon shell is uniformly coated on the CuO nanowire cores. As an anode of lithium ion batteries, the resultant CuO/C nanowire arrays are demonstrated to have high specific capacity (672 mAh·g−1 at 0.2 C) and good cycle stability (425 mAh·g−1 at 1 C up to 150 cycles). The core/shell arrays structure plays positive roles in the enhancement of Li ion storage due to fast ion/electron transfer path, good strain accommodation and sufficient contact between electrolyte and active materials.

Synthesis of shish-kebab-like NiO@Co3O4 nanowire arrays and their application for electrochemical energy storage

Multicomponent hetero-structured metal oxide arrays are playing important roles in the development of advanced optical and electrochemical devices. Herein, we report shish-kebab-like NiO@Co3O4 nanowire arrays by a simple two-step hydrothermal method. Interestingly, lots of hexagonal NiO nanoflakes are randomly assembled on the preformed Co3O4 nanowire arrays forming a shish-kebab-like architecture. As cathode of alkaline battery, the as-prepared NiO@Co3O4 nanowire arrays exhibit a specific capacity of 89mAhg−1 at 1.25Ag−1 and 75mAh g−1 at 20Ag−1, respectively. The unique architecture provides higher reaction surface area resulting in higher capacity.

Hydrothermal synthesis of mesoporous metal oxide arrays with enhanced properties for electrochemical energy storage

Mesoporous nanowall NiO arrays are prepared by a facile hydrothermal synthesis method with a following annealing process. The NiO nanowall shows continuous mesopores ranging from 5 to 10nm and grows vertically on the substrate forming a porous net-like structure with macropores of 20–300nm. A plausible mechanism is proposed for the growth of mesoporous nanowall NiO arrays. As cathode material of pseudocapacitors, the as-prepared mesoporous nanowall NiO arrays show good pseudocapacitive performances with a high capacitance of 600Fg−1 at 2Ag−1 and impressive high-rate capability with a specific capacitance of 338Fg−1 at 40Ag−1. In addition, the mesoporous nanowall NiO arrays possess good cycling stability. After 6000 cycles at 2Ag−1, a high capacitance of 660Fg−1 is attained, and no obvious degradation is observed. The good electrochemical performance is attributed to its highly porous morphology, which provides large reaction surface and short ion diffusion paths, leading to enhanced electrochemical properties.

Improved charge transport in inverted polymer solar cells using surface engineered ZnO-nanorod array as an electron transport layer

Interface control is an important issue in polymer based solar cells because the influence of interface property on bulk heterojunction transport can govern the device performance. We systematically select a series of thioaromatic molecules to tune the surface characters of the metal-oxide array in inverted ZnO-nanorod/poly(3-hexythiophene):(6,6)-phenyl C61 butyric acid methyl ester (P3HT:PCBM)/Ag devices. In addition to physically improving the compatibility between ZnO-nanorod and polymer blend contact junction, those conjugated thioaromatic molecules slightly modulate the nanostructured donor and acceptor percolated networks as revealed by the measured carrier mobility values whereas the modulations of photon absorption efficiency and the exciton dissociation rate are negligible. The balanced charge transport architecture can be obtained by using longer and linearly arranged aromatic rings. Additionally, both series resistance and shunt resistance are also improved. As high as ~80% enhancement in power conversion efficiency of the device has been achieved. The result decouples the contribution of the exciton dissociation rate from the bulk heterojunction charge transport process to device performance in inverted polymer solar cells and can be generalized to hybrid polymer-nanocrystal systems as well.

Relating nanomaterial properties and microbial toxicity

Metal and metal oxide nanoparticles are among the most commonly used nanomaterials and their potential for adversely affecting environmental systems raises concern. Complex microbial consortia underlie environmental processes, and the potential toxicity of nanoparticles to microbial systems, and the consequent impacts on trophic balances, is particularly worrisome. The diverse array of metal and metal oxides, the different sizes and shapes that can be prepared and the variety of possible surface coatings complicate assessments of toxicity. Further muddling biocidal interpretations are the diversity of microbes and their intrinsic tolerances to stresses. Here, we review a range of studies focused on nanoparticle-microbial interactions in an effort to correlate the physical-chemical properties of engineered metal and metal oxide nanoparticles to their biological response. General conclusions regarding the parent material of the nanoparticle and the nanoparticle's size and shape on potential toxicity can be made. However, the surface coating of the material, which can be altered significantly by environmental conditions, can ameliorate or promote microbial toxicity. Understanding nanoparticle transformations and how the nanoparticle surface can be designed to control toxicity represents a key area for further study. Additionally, the vast array of microbial species and the structuring of these species within communities complicate extrapolations of nanoparticle toxicity in real world settings. Ultimately, to interpret the effect and eventual fate of engineered materials in the environment, an understanding of the relationship between nanoparticle properties and responses at the molecular, cellular and community levels will be essential.