Promotion of Cobalt Oxide Catalysts by Acid-Etching and Ruthenium Incorporation for Chlorinated VOC Oxidation

In this work, Ru-promoted cobalt oxide catalysts with a nanotube morphology were prepared by a synthesis route based on the Kirkendall effect followed by an acid treatment and subsequent optimized Ru impregnation. The resulting samples were thoroughly characterized by means of N2 physisorption, X-ray energy-dispersive spectroscopy, X-ray diffraction, scanning electron microscopy techniques, X-ray photoelectron spectroscopy, and temperature-programmed techniques (O2-temperature-programmed desorption, H2-temperature-programmed reduction, and temperature-programmed oxidation) and evaluated in the gas-phase oxidation of 1,2-dichloroethane. It has been demonstrated that Ru addition improves the oxygen mobility as well as the amount of Co2+ and Oads species at the surface by the formation of the Ru-O-Co bond, which in turn governs the performance of the catalysts in the oxidation reaction. Moreover, the acid-etching favors the dispersion of the Ru species on the surface of the catalysts and strengthens the interaction among the noble metal and the cobalt oxide, thereby improving the thermal stability of the Ru-promoted oxides. Thus, the resulting catalysts are not only active, as the chlorinated pollutant is efficiently converted into deep oxidation products at relatively low temperatures, but also quite stable when operating for 120 h.

Chemical conversion based on the crystal facet effect of transition metal oxides and construction methods for sharp-faced nanocrystals

In-depth research has found that the nanocrystal facet of transition metal oxides (TMOs) greatly affects their heterogeneous catalytic performance, as well as the property of photocatalysis, gas sensing, electrochemical reaction, etc. that are all involved in chemical conversion processes. Therefore, the facet-dependent properties of TMO nanocrystals have been fully and carefully studied by combining systematic experiments and theoretical calculations, and mechanisms of chemical reactions are accurately explained at the molecular level, which will be closer to the essence of reactions. Evidently, as an accurate investigation on crystal facets, well-defined TMO nanocrystals are the basis and premise for obtaining relevant credible results, and shape-controlled synthesis of TMO nanocrystals thereby has received great attention and development. The success in understanding of facet-dependent properties and shape-controlled synthesis of TMO nanocrystals is highly valuable for the control of reaction and the design of high-efficiency TMO nanocrystal catalysts as well as other functional materials in practical applications.

Molten Salt Assisted Self-Assembly: Synthesis of Mesoporous LiCoO2 and LiMn2 O4 Thin Films and Investigation of Electrocatalytic Water Oxidation Performance of Lithium Cobaltate

Mesoporous thin films of transition metal lithiates (TML) belong to an important group of materials for the advancement of electrochemical systems. This study demonstrates a simple one pot method to synthesize the first examples of mesoporous LiCoO₂ and LiMn₂ O₄ thin films. Molten salt assisted self-assembly can be used to establish an easy route to produce mesoporous TML thin films. The salts (LiNO₃ and [Co(H₂ O)₆ ](NO₃ )₂ or [Mn(H₂ O)₄ ](NO₃ )₂ ) and two surfactants (10-lauryl ether and cethyltrimethylammonium bromide (CTAB) or cethyltrimethylammonium nitrate (CTAN)) form stable liquid crystalline mesophases. The charged surfactant is needed for the assembly of the necessary amount of salt in the hydrophilic domains of the mesophase, which produces stable metal lithiate pore-walls upon calcination. The films have a large pore size with a high surface area that can be increased up to 82 m² g^-1 . The method described can be adopted to synthesize other metal oxides and metal lithiates. The mesoporous thin films of LiCoO₂ show promising performance as water oxidation catalysts under pH 7 and 14 conditions. The electrodes, prepared using CTAN as the cosurfactant, display the lowest overpotentials in the literature among other LiCoO₂ systems, as low as 376 mV at 10 mA cm^-2 and 282 mV at 1 mA cm^-2 .

Conversion Reaction-Based Oxide Nanomaterials for Lithium Ion Battery Anodes

Developing high-energy-density electrodes for lithium ion batteries (LIBs) is of primary importance to meet the challenges in electronics and automobile industries in the near future. Conversion reaction-based transition metal oxides are attractive candidates for LIB anodes because of their high theoretical capacities. This review summarizes recent advances on the development of nanostructured transition metal oxides for use in lithium ion battery anodes based on conversion reactions. The oxide materials covered in this review include oxides of iron, manganese, cobalt, copper, nickel, molybdenum, zinc, ruthenium, chromium, and tungsten, and mixed metal oxides. Various kinds of nanostructured materials including nanowires, nanosheets, hollow structures, porous structures, and oxide/carbon nanocomposites are discussed in terms of their LIB anode applications.

Structure-Dependent Anchoring of Organic Molecules to Atomically Defined Oxide Surfaces: Phthalic Acid on Co3O4(111), CoO(100), and CoO(111)

We have performed a model study to explore the influence of surface structure on the anchoring of organic molecules on oxide materials. Specifically, we have investigated the adsorption of phthalic acid (PA) on three different, well-ordered, and atomically defined cobalt oxide surfaces, namely 1) Co3O4(111), 2) CoO(111), and 3) CoO(100) on Ir(100). PA was deposited by physical vapor deposition (PVD). The formation of the PA films and interfacial reactions were monitored in situ during growth by isothermal time-resolved IR reflection absorption spectroscopy (TR-IRAS) under ultrahigh vacuum (UHV) conditions. We observed a pronounced structure dependence on the three surfaces with three distinctively different binding geometries and characteristic differences depending on the temperature and coverage. 1) PA initially binds to Co3O4(111) through the formation of a chelating bis-carboxylate with the molecular plane oriented perpendicularly to the surface. Similar species were observed both at low temperature (130 K) and at room temperature (300 K). With increasing exposure, chelating mono-carboxylates became more abundant and partially replaced the bis-carboxylate. 2) PA binds to CoO(100) in the form of a bridging bis-carboxylate for low coverage. Upon prolonged deposition of PA at low temperature, the bis-carboxylates were converted into mono-carboxylate species. In contrast, the bis-carboxylate layer was very stable at 300 K. 3) For CoO(111) we observed a temperature-dependent change in the adsorption mechanism. Although PA binds as a mono-carboxylate in a bridging bidentate fashion at low temperature (130 K), a strongly distorted bis-carboxylate was formed at 300 K, possibly as a result of temperature-dependent restructuring of the surface. The results show that the adsorption geometry of PA depends on the atomic structure of the oxide surface. The structure dependence can be rationalized by the different arrangements of cobalt ions at the three surfaces.

Hierarchically ordered mesoporous Co3O4 materials for high performance Li-ion batteries

Highly ordered mesoporous Co₃O₄ materials have been prepared via a nanocasting route with three-dimensional KIT-6 and two-dimensional SBA-15 ordered mesoporous silicas as templates and Co(NO₃)₂ · 6H₂O as precursor. Through changing the hydrothermal treating temperature of the silica template, ordered mesoporous Co₃O₄ materials with hierarchical structures have been developed. The larger pores around 10 nm provide an efficient transport for Li ions, while the smaller pores between 3–5 nm offer large electrochemically active areas. Electrochemical impedance analysis proves that the hierarchical structure contributes to a lower charge transfer resistance in the mesoporous Co₃O₄ electrode than the mono-sized structure. High reversible capacities around 1141 mAh g⁻¹ of the hierarchically mesoporous Co₃O₄ materials are obtained, implying their potential applications for high performance Li-ion batteries.

Facile synthesis of NiCoMnO4 nanoparticles as novel electrode materials for high-performance asymmetric energy storage devices

Hydrothermally synthesized NiCoMnO₄ NPs showed a high capacitance of 510 F g⁻¹ with high mass loaded electrodes (∼10 mg cm⁻²). Integrated with RGO NSs, their viability was testified for high-performance asymmetric supercapacitors.

Synthesis of organized mesoporous metal oxide films templated by amphiphilic PVA–PMMA comb copolymer

We present a synthesis of organized mesoporous metal oxide films with high porosity and good interconnectivity using an amphiphilic PVA–PMMA comb copolymer which can be a promising template as an alternative to conventional block copolymers.

Mesoporous materials for clean energy technologies

Alternative energy technologies are greatly hindered by significant limitations in materials science. From low activity to poor stability, and from mineral scarcity to high cost, the current materials are not able to cope with the significant challenges of clean energy technologies. However, recent advances in the preparation of nanomaterials, porous solids, and nanostructured solids are providing hope in the race for a better, cleaner energy production. The present contribution critically reviews the development and role of mesoporosity in a wide range of technologies, as this provides for critical improvements in accessibility, the dispersion of the active phase and a higher surface area. Relevant examples of the development of mesoporosity by a wide range of techniques are provided, including the preparation of hierarchical structures with pore systems in different scale ranges. Mesoporosity plays a significant role in catalysis, especially in the most challenging processes where bulky molecules, like those obtained from biomass or highly unreactive species, such as CO2 should be transformed into most valuable products. Furthermore, mesoporous materials also play a significant role as electrodes in fuel and solar cells and in thermoelectric devices, technologies which are benefiting from improved accessibility and a better dispersion of materials with controlled porosity.

Interwoven three-dimensional architecture of cobalt oxide nanobrush-graphene@Ni(x)Co(2x)(OH)(6x) for high-performance supercapacitors

Development of pseudocapacitor electrode materials with high comprehensive electrochemical performance, such as high capacitance, superior reversibility, excellent stability, and good rate capability at the high mass loading level, still is a tremendous challenge. To our knowledge, few works could successfully achieve the above comprehensive electrochemical performance simultaneously. Here we design and synthesize one interwoven three-dimensional (3D) architecture of cobalt oxide nanobrush-graphene@Ni(x)Co(2x)(OH)(6x) (CNG@NCH) electrode with high comprehensive electrochemical performance: high specific capacitance (2550 F g(-1) and 5.1 F cm(-2)), good rate capability (82.98% capacitance retention at 20 A g(-1) vs 1 A g(-1)), superior reversibility, and cycling stability (92.70% capacitance retention after 5000 cycles at 20 A g(-1)), which successfully overcomes the tremendous challenge for pseudocapacitor electrode materials. The asymmetric supercapacitor of CNG@NCH//reduced-graphene-oxide-film exhibits good rate capability (74.85% capacitance retention at 10 A g(-1) vs 0.5 A g(-1)) and high energy density (78.75 Wh kg(-1) at a power density of 473 W kg(-1)). The design of this interwoven 3D frame architecture can offer a new and appropriate idea for obtaining high comprehensive performance electrode materials in the energy storage field.

Ordered mesoporous NiO with thin pore walls and its enhanced sensing performance for formaldehyde

A class of formaldehyde (HCHO) gas sensors with a high response were developed based on ordered mesoporous NiO, which were synthesized via the nanocasting route by directly using mesoporous silica as the hard template. A series of mesoporous NiO with different textural parameters such as specific surface area, pore size, pore wall thickness were achieved by selecting mesoporous silica with different pore sizes as templates. The gas sensing properties for formaldehyde (HCHO) of the NiO specimens were examined. The results show that this mesoporous NiO possesses a much higher response to HCHO even at low concentration levels than the bulk NiO, and a larger specific surface area and pore size as well as thinner pore walls would be beneficial for enhancing the sensing properties of NiO.

Designing 3D highly ordered nanoporous CuO electrodes for high-performance asymmetric supercapacitors

The increasing demand for energy has triggered tremendous research efforts for the development of lightweight and durable energy storage devices. Herein, we report a simple, yet effective, strategy for high-performance supercapacitors by building three-dimensional pseudocapacitive CuO frameworks with highly ordered and interconnected bimodal nanopores, nanosized walls (∼4 nm) and large specific surface area of 149 m(2) g(-1). This interesting electrode structure plays a key role in providing facilitated ion transport, short ion and electron diffusion pathways and more active sites for electrochemical reactions. This electrode demonstrates excellent electrochemical performance with a specific capacitance of 431 F g(-1) (1.51 F cm(-2)) at 3.5 mA cm(-2) and retains over 70% of this capacitance when operated at an ultrafast rate of 70 mA cm(-2). When this highly ordered CuO electrode is assembled in an asymmetric cell with an activated carbon electrode, the as-fabricated device demonstrates remarkable performance with an energy density of 19.7 W h kg(-1), power density of 7 kW kg(-1), and excellent cycle life. This work presents a new platform for high-performance asymmetric supercapacitors for the next generation of portable electronics and electric vehicles.

Ligand-assisted soft-chemical synthesis of self-assembled different shaped mesoporous Co3O4: efficient visible light photocatalysts

Mesoporous self-assembled cobalt oxide (Co₃O₄) of different shapes was synthesized by a facile soft-chemical process using cobalt nitrate, oxalic acid and phosphoric acid in the presence of cationic templates, cetyltrimethylammonium bromide, 1-butyl-3-methylimidazolium bromide, and pyridinium bromide at 75 °C/2 h followed by calcination at 300 °C.

In situ fabrication of graphene decorated microstructured globe artichokes of partial molar nickel cobaltite anchored on a Ni foam as a high-performance supercapacitor electrode

3D microstructured globe artichokes of a rGO/Ni_0.3Co_2.7O₄ composite were synthesized through a hydrothermal method to contribute an efficient work nature as supercapacitor electrodes.

Magnetic studies of mesoporous nanostructured iron oxide materials synthesized by one-step soft-templating

A combined magnetization and ⁵⁷Fe spin-echo nuclear magnetic resonance (NMR) study has been carried out on mesoporous nanostructured materials consisting of the magnetite (Fe₃O₄) and maghemite (γ-Fe₂O₃) phases.

Hierarchical NiAl layered double hydroxide/multiwalled carbon nanotube/nickel foam electrodes with excellent pseudocapacitive properties

The performances of pseudocapacitors usually depend heavily on their hierarchical architectures and composition. Herein, we report a three-dimensional hierarchical NiAl layered double hydroxide/multiwalled carbon nanotube/nickel foam (NiAl-LDH/MWCNT/NF) electrode prepared by a facile three-step fabrication method: in situ hydrothermal growth of NiAl-LDH film on a Ni foam, followed by direct chemical vapor deposition growth of dense MWCNTs onto the NiAl-LDH film, and finally the growth of NiAl-LDH onto the surface of the MWCNTs via an in situ hydrothermal process in the presence of surfactant sodium dodecyl sulfate. The MWCNT surface was fully covered by NiAl-LDH hexagonal platelets, and this hierarchical architecture led to a much enhanced capacitance. The NiAl-LDH/MWCNT/NF electrode has an areal loading mass of 5.8 mg of LDH per cm(2) of MWCNT/NF surface. It also possesses exceptional areal capacitance (7.5 F cm(-2)), specific capacitance (1293 F g(-1)), and cycling stability (83% of its initial value was preserved after 1000 charge-discharge cycles). The NiAl-LDH/MWCNT/NF material is thus a highly promising electrode with potential applications in electrochemical energy storage.

Scalable one-pot bacteria-templating synthesis route toward hierarchical, porous-Co3O4 superstructures for supercapacitor electrodes

Template-driven strategy has been widely used to synthesize inorganic nano/micro materials. Here, we used a bottom-up controlled synthesis route to develop a powerful solution-based method of fabricating three-dimensional (3D), hierarchical, porous-Co₃O₄ superstructures that exhibit the morphology of flower-like microspheres (hereafter, RT-Co₃O₄). The gram-scale RT-Co₃O₄ was facilely prepared using one-pot synthesis with bacterial templating at room temperature. Large-surface-area RT-Co₃O₄ also has a noticeable pseudocapacitive performance because of its high mass loading per area (~10 mg cm⁻²), indicating a high capacitance of 214 F g⁻¹ (2.04 F cm⁻²) at 2 A g⁻¹ (19.02 mA cm⁻²), a Coulombic efficiency averaging over 95%, and an excellent cycling stability that shows a capacitance retention of about 95% after 4,000 cycles.

3D ordered nanoporous NiMoO4 for high-performance supercapacitor electrode materials

3D ordered nanocrystalline nanoporous NiMoO₄ with high surface area and bimodal pore size distribution has been synthesized by nanocasting from mesoporous silica KIT-6, and applied as high-performance supercapacitor electrode material.

Synthesis of morphology controllable porous Co3O4 nanostructures with tunable textural properties and their catalytic application

Co₃O₄ nanostructures with controllable morphology and tunable textural properties synthesized via an aqueous based route in the absence of templating agents were found to be effective catalysts.

Gold nanoparticles embedded within mesoporous cobalt oxide enhance electrochemical oxygen evolution

Gold nanoparticles incorporated in mesoporous cobalt oxides (Au/mCo3 O4 ) are fabricated by a nanocasting method using porous silica as the hard template. The Au/mCo3 O4 material exhibits enhanced catalytic activity towards water oxidation compared to bulk mCo3 O4 in both alkaline and neutral solutions. The superior catalytic performance is ascribed to the synergistic effect of electronegative metal gold, which facilitates the generation of active Co(IV) sites, as well as the large specific surface area and the preferential exposure of catalytic active crystalline lattice.

Single-crystalline bilayered V2O5 nanobelts for high-capacity sodium-ion batteries

Single-crystalline bilayered vanadium oxide nanobelts were synthesized by a simple solvothermal method. FESEM and AFM analyses identified the nanobelt morphology of the as-prepared vanadium oxide with a rectangular cross-section and a thickness of approximately 50 nm. XRD and TEM characterizations revealed the presence of a large (001) interlayer spacing (∼11.53 Å), which can accommodate Na-ion insertion and extraction. When applied as cathode materials in Na-ion batteries, vanadium oxide nanobelts exhibited a high capacity of 231.4 mA h g(-1) at a current density of 80 mA g(-1). This corresponds to the theoretical capacity to form Na2V2O5 on Na-ion insertion. Vanadium oxide nanobelts also demonstrated an excellent high-rate performance and a satisfactory cyclability. These superior electrochemical performances could be ascribed to the unique bilayered vanadium oxide nanobelts with dominantly exposed {100} crystal planes, which provide large interlayer spacing for facile Na-ion insertion/extraction. Single-crystalline bilayered vanadium oxide nanobelts could be promising cathode materials for high-performance Na-ion batteries.

Controlled 3D-coating of the pores of highly ordered mesoporous antiferromagnetic Co3O4 replicas with ferrimagnetic Fe(x)Co(3-x)O4 nanolayers

The controlled filling of the pores of highly ordered mesoporous antiferromagnetic Co3O4 replicas with ferrimagnetic FexCo3-xO4 nanolayers is presented as a proof-of-concept toward the integration of nanosized units in highly ordered, heterostructured 3D architectures. Antiferromagnetic (AFM) Co3O4 mesostructures are obtained as negative replicas of KIT-6 silica templates, which are subsequently coated with ferrimagnetic (FiM) FexCo3-xO4 nanolayers. The tuneable magnetic properties, with a large exchange bias and coercivity, arising from the FiM/AFM interface coupling, confirm the microstructure of this novel two-phase core-shell mesoporous material. The present work demonstrates that ordered functional mesoporous 3D-materials can be successfully infiltrated with other compounds exhibiting additional functionalities yielding highly tuneable, versatile, non-siliceous based nanocomposites.

Ordered Porous Nanomaterials: The Merit of Small

This paper will introduce the reader to some of the “classical” and “new” families of ordered porous materials which have arisen throughout the past decades and/or years. From what is perhaps the best-known family of zeolites, which even now to this day is under constant research, to the exciting new family of hierarchical porous materials, the number of strategies, structures, porous textures, and potential applications grows with every passing day. We will attempt to put these new families into perspective from a synthetic and applied point of view in order to give the reader as broad a perspective as possible into these exciting materials.

Bipolar resistive switching in p-type Co3O4 nanosheets prepared by electrochemical deposition

Metal oxide nanosheets have potential applications in novel nanoelectronics as nanocrystal building blocks. In this work, the devices with a structure of Au/p-type Co3O4 nanosheets/indium tin oxide/glass having bipolar resistive switching characteristics were successfully fabricated. The experimental results demonstrate that the device have stable high/low resistance ratio that is greater than 25, endurance performance more than 200 cycles, and data retention more than 10,000 s. Such a superior performance of the as-fabricated device could be explained by the bulk film and Co3O4/indium tin oxide glass substrate interface effect.

Surfactant-free scalable synthesis of hierarchically spherical Co3O4 superstructures and their enhanced lithium-ion storage performances

Unique hierarchically porous spherical Co(3)O(4) superstructures were synthesized via a surfactant-free hydrothermal process followed by a calcination treatment, in which the concentration of reactant cobalt (II) nitrate hexahydrate is a key factor affecting the morphology of products. X-ray powder diffraction, electron microscopies (TEM and SEM), and thermogravimetric analysis were employed to investigate the formation of Co(3)O(4) spherical superstructures. Our results suggest that they formed from numerous cubic Co(3)O(4) nanocrystals via an oriented attachment mechanism. These superstructures exhibit a high specific capacity of 1750 mA h g(-1) after the first charge-discharge cycle, and the capacity retention remains at a constant of 1600 mA h g(-1) at 0.2 C after 50 cycles. The facile, scalable, energy-efficient and environmentally friendly nature of the presented approach renders it particularly attractive from a technological standpoint. In addition, this scalable and facile synthesis method could be extended to the preparation of other transition metal oxides with specific morphologies and surface textures.

Facile shape control of Co(3)O(4) and the effect of the crystal plane on electrochemical performance

Co(3)O(4) with three different crystal plane structures - cubes bounded by {001}planes, truncated octahedra enclosed by {111} and {001} planes, and octahedra with exposed {111}planes - is synthesized using a very simple one-step hydrothermal method. The three kinds of Co(3)O(4) exhibit significantly different electrochemical performances and the effect of different exposed crystal planes on the electrochemical performance of Co(3)O(4) is comprehensively studied.

Ordered mesoporous metal oxides: synthesis and applications

Great progress has been made in the preparation and application of ordered mesoporous metal oxides during the past decade. However, the applications of these novel and interesting materials have not been reviewed comprehensively in the literature. In the current review we first describe different methods for the preparation of ordered mesoporous metal oxides; we then review their applications in energy conversion and storage, catalysis, sensing, adsorption and separation. The correlations between the textural properties of ordered mesoporous metal oxides and their specific performance are highlighted in different examples, including the rate of Li intercalation, sensing, and the magnetic properties. These results demonstrate that the mesoporosity has a direct impact on the properties and potential applications of such materials. Although the scope of the current review is limited to ordered mesoporous metal oxides, we believe that the information may be useful for those working in a number of fields.

Mesoporous nickel oxide nanowires: hydrothermal synthesis, characterisation and applications for lithium-ion batteries and supercapacitors with superior performance

Mesoporous nickel oxide nanowires were synthesized by a hydrothermal reaction and subsequent annealing at 400 °C. The porous one-dimensional nanostructures were analysed by field-emission SEM, high-resolution TEM and N(2) adsorption/desorption isotherm measurements. When applied as the anode material in lithium-ion batteries, the as-prepared mesoporous nickel oxide nanowires demonstrated outstanding electrochemical performance with high lithium storage capacity, satisfactory cyclability and an excellent rate capacity. They also exhibited a high specific capacitance of 348 F g(-1) as electrodes in supercapacitors.