Flake-like MoS2 nano-architecture and its nanocomposite with reduced Graphene Oxide for hybrid supercapacitors applications

In this article, we have synthesized flake-like MoS₂ nanoarchitecture by urea assisted hydrothermal method. To improve the electrical and electrochemical properties of MoS₂ nanoarchitecture, we formed its nanocomposite (MoS₂/r-GO) with 10% r-GO. After the addition of 10% r-GO, the nanocomposite shows the electrical conductivity of 1.24 × 10⁻¹ Sm⁻¹ that is higher than the pure MoS₂ (2.2 × 10⁻⁷ Sm⁻¹). The prepared nanocomposite also showed higher specific capacitance (441 Fg^-1 at 1 Ag^-1) than the pure MoS₂ nanoarchitecture (248 Fg^-1 at 1 Ag^-1). Moreover, nanocomposite lost just 15.8% of its initial capacitance after 1000 charge-discharge cycles. The enhanced electrochemical activity of the nanocomposite is due to its unique flake-like structure and its reduced charge transfer resistance (Rct ~ 23.5 Ω). The 2-D flake-like structure of the electrode increased its contact area with the r-GO matrix and electrolyte. The higher electrical conductivity and specific surface area of the nanocomposite facilitated the faradaic and non-faradic charge storage mechanism. The r-GO matrix not only acted as a capacitive supplement but also facilitated the redox reaction because of its superior electrical conductivity. As the nanocomposite showed CV and CCD profiles in the negative potential window (−1 V to −0.53 V), therefore it has the potential to be used as a negative electrode material for hybrid supercapacitors applications. The observed results revealed the potential of the (MoS₂/r-GO) nanocomposite-based cathode for hybrid supercapacitor applications.     

Electrochemical and textural characterization of binary Ru-Sn oxides synthesized under mild hydrothermal conditions for supercapacitors

Hydrous ruthenium-tin oxides (denoted as (Ru-Sn)O₂·nH₂O) were synthesized under a mild hydrothermal condition. The mean particles size of pristine RuO₂·nH₂O, smaller than 3 nm, was decreased with the introduction of Sn into the precursor solutions while it is not significantly affected by varying the Sn content. The textual characteristics of (Ru-Sn)O₂·nH₂O were analyzed through means of X-ray diffraction (XRD), energy-dispersive spectroscopy (EDS), electron diffraction, X-ray photoelectron spectroscopy (XPS), and thermogravimetric analyses (TGA). From the ideal capacitive behavior of pristine oxides with the Ru content ≥40 at.%, hydrothermal synthesis favored the formation of hydrous oxides with a novel structure providing excellent pathways for electron hopping and proton diffusion/exchange during the charge storage/delivery process. The introduction of tin oxide was demonstrated to successfully promote the utilization of oxyruthenium species, reaching a maximum C_S,Ru of ca. 830 F/g for pristine Ru_0.6Sn_0.4O₂·nH₂O (measured at 25 mV/s).     

Fabrication of nickel oxide-embedded titania nanotube array for redox capacitance application

Titania nanotube array with an enlarged tube diameter of 110 nm and length of 700 nm was grown on titanium metal by a potentiostatic anodization in hydrofluoric acid-phosphoric acid-ethenyl glycol electrolyte. Nickel hydroxide was introduced into this titania nanotubes by either an electrodeposition-oxidation or hydrothermal process. Nickel oxide-titania composite was finally formed by heating treatment at 300 °C. Such a well-defined nanocomposite supported on titanium substrate was designed as a functional nanotube array electrode for the redox capacitance application. The morphology, microstructure and electrochemical properties of the nanocomposites were investigated by field emission scanning electron microscope, X-ray diffraction, energy dispersive X-ray diffraction and cyclic voltammetry measurements. It was found that nickel oxide could be embedded in titania nanotubes and extend from inner wall to top layer with an open pore mouth. The entire tube lengths were approx. 770 nm and 710 nm, meanwhile nickel-to-titanium atom ratios were determined as 9.6 at% and 36.4 at% for nickel oxide-embedded titania by an electrochemical and hydrothermal synthesis, respectively. The corresponding specific redox capacitance was also increased from 26 mF cm⁻² to 85 mF cm⁻² with highly reversible charge-discharge stability. Such an improvement was mostly ascribed to more accessible reaction interface of electroactive nickel oxide through its higher loading and a uniform dispersion on titania nanotubes. The capacitance was further increased up to 128 mF cm⁻² for 36.4 at% nickel-containing nickel oxide-titania/titanium electrode when a porous graphite carbon instead of a platinum sheet was used as a cathode.     

Ru oxide/carbon nanotube composites for supercapacitors prepared by spontaneous reduction of Ru(VI) and Ru(VII)

A novel method based on spontaneous reduction of Ru(VI) and Ru(VII) is reported for the deposition of Ru oxide on multi-walled carbon nanotubes (MWCNT). Both purified and acid functionalized nanotubes (p-MWCNT and a-MWCNT) have been used to produce composite materials for use in high power aqueous supercapacitors. Specific capacitances of 213 ± 16 F g⁻¹ and 184 ± 11 F g⁻¹ were obtained for Ru oxide/p-MWCNT and Ru oxide/a-MWCNT composites, respectively. Specific capacitances for the Ru oxide component were 704 ± 62 F g⁻¹ and 803 ± 72 F g⁻¹, respectively. Current vs. potential curves exhibited capacitance peaks at ca. +0.5 V vs. Ag/AgCl. The Ru oxide/p-MWCNT composite was shown to be stable over 20,000 charge/discharge cycles. An advantage of the method is that no pre-treatment of the MWCNT is required for optimum performance.     

金属化合物超级电容器电极材料

金属化合物是理想的赝电容电极材料,但是其拥有导电性差且易团聚的缺点,使得电容性能显著下降。本文通过总结近年来的研究成果,阐述了金属化合物在超级电容器中的应用以及提高各类金属化合物电容性能的方法。研究表明,金属化合物与各类材料的复合、电沉积法、化合物结构的定向合成等多种方法均可有效提高金属化合物导电性,防止团聚现象的发生。随着金属化合物缺点的不断攻克,其在超级电容器的应用也将逐渐频繁起来,同时金属化合物赝也为新兴的储能元件注入了新的活力。     

Aqueous route for mesoporous metal oxides using inorganic metal source and their applications

In this paper, we report a synthetic route for mesoporous metal oxides from inorganic metal sources in aqueous media. This synthesis route offers a versatile, low cost and environmental friendly method to produce mesoporous metal oxides that have very high surface areas. As an example, the synthesis of iron oxide is described in detail. Synthesis conditions including aging time, aging temperature and amount of urea were varied to find the optimal synthesis conditions. We found that recycling the Cetyltrimethylammonium Bromide (CTAB) template is possible when the amount of urea is reduced to stoichiometric. The mesoporous metal oxides made under these conditions are self assemblies of leaf-like single crystal sub-units with randomly distributed mesopores embedded into the crystals. As a result of the crystalline nature, these mesoporous metal oxides have high thermal stabilities and their applications as gas sensors and CO disproportionation catalysts indicate promising aspects of these materials.     

Facile synthesis of hybrid nanocomposite based on chitosan binary metal oxides for high-performance supercapacitor

The advancement in materials for energy storage for supercapacitors has been supported by the current shortage of energy as well as the increasing availability of sources of clean energy. Consequently, two-dimensional materials based on metal oxide nanoparticles (copper oxide (CuO) and zinc oxide (ZnO), have great potential for the previously discussed utilization. A simple and affordable solid-state approach was employed to design hybrid nanocomposite based on chitosan (Cs) blended with ZnO and CuO; this nanocomposite was labeled with CZC. The structural, morphological investigation of CZC hybrid nanocomposites, and X-ray diffraction (XRD) of the prepared nanocomposites were characterized. Consequently, hybrid nanocomposites for application as electrodes for supercapacitor devices were developed. The hybrid nanocomposite (CZC-3) shows improved cycle stability, high energy density, and a specific capacitance in the electrochemical activity. Remaining at 97.8% of the initial capacitance even after 5000 cycles. These results imply that the hybrid nanocomposite based on Cs/ZnO/CuO has a promising future as a supercapacitor electrode material. Additionally, it provides superior performance to other nanocomposites with a high specific capacitance of 638.3 F/g and about 86.98% capacity retention after 5000 cycles at a current density of 1 A/g.     

Hydrothermal synthesis of binary Ru-Ti oxides with excellent performances for supercapacitors

Hydrous, crystalline, binary (Ru-Ti)O₂·nH₂O with compositions equal to the ratios of metallic ions in the precursor solutions are successfully synthesized by a mild hydrothermal process. The maximum utilization of RuO₂·nH₂O (ca. 793 F/g) occurs at the composition of 60 M% TiO₂·nH₂O although phase separation is clearly found for this TiO₂-enriched binary oxides. The nano-structured architecture with a high BET surface area (ca. 253 m²/g) of the hydrothermal-derived (Ru-Ti)O₂·nH₂O with annealing at 200 °C favors the physical adsorption of water and maintains a high water content which is novel and never found before. Due to this novel nanostructure, the annealed (Ru-Ti)O₂·nH₂O synthesized by means of the hydrothermal process exhibits excellent performances (i.e., high utilization of RuO₂, high power property, and long cycle life) for supercapacitors.     

Nanosheet-like MoO3 and conductive PANI electrodeposited on flexible carbon cloth for self-supported solid-state supercapacitor electrode

In this paper, uniformly transition metal oxide (MoO₃) nanosheets were electrochemically deposited on flexible carbon cloth (CC), and then conductive polyaniline (PANI) was orderly wrapped around their surface by electrochemical polymerization. The morphology and structure of as-obtained self-supported PANI/MoO₃/CC electrode were investigated by FTIR, X-ray diffraction, Raman, scanning electron microscope (SEM), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy measurements in detail. Among all PANI/MoO₃/CC electrode, the self-supported PMC-3 (deposition time of 300 s) has high specific capacitance of 841.6 F g⁻¹ at current density of 0.5 A g⁻¹ in the three-electrode system, having specific capacitance of 595.7 F g⁻¹ even at 10 A g⁻¹. Novelty, the as-assembled symmetrical capacitor is flexible and convenient with power density of 199.93 W kg⁻¹ at the energy density of 9.69 Wh kg⁻¹ and the energy density of 3.88 Wh kg⁻¹ at power density of 4000 W kg⁻¹. Thus, the electrochemical properties of the self-supported PANI/MoO₃/CC electrode were significantly improved, and the self-supported electrodes are more competitive than other materials in practical application of clean energy storage systems.     

Catalytic combustion of benzene over metal oxides supported on SBA-15

The catalytic combustion of benzene over metal oxides supported on SBA-15 was investigated. The catalysts were prepared by the incipient wetness method and characterized by XRD, BET, TEM, ESR and TPR. The calcined siliceous SBA-15 and CuO/SBA-15 samples displayed well-resolved patterns with a sharp peak at about 1.0°. It is clear that the loading of CuO on the silica matrix drastically decreases the surface area and pore volume of the catalysts, as would be expected for the incorporation of CuO. Among the supported metal oxides, CuO supported on SBA-15 was found to have the highest activity for benzene oxidation. In addition, copper oxide supported on SBA-15 gives higher catalytic activity than copper oxide supported on MCM-41. From the ESR results, the CuO dispersed on the SBA-15 acts as the active site of the CuO/SBA-15 catalysts in the oxidative decomposition of benzene. The catalytic activity gradually increases with increasing CuO loading on SBA-15.     

Synthesis of La1-xGdxFe1-yCoyO3/r-GO nanocomposite with integrated features for the treatment of hazardous industrial effluents

Solar-light triggered semiconductive materials with a small bandgap, a low electron-hole pair recombination rate, and quicker charge carrier characteristics are very efficient catalysts for hazardous industrial effluent treatment. Herein, we adopted wet-chemical and ultra-sonication techniques to prepare binary metal (Gd & Co) doped Lanthanum ferrite (GCLFO) nanoparticles and their reduced-graphene (r-GO) based nanocomposite (GCLFO/r-GO) as an ideal photocatalyst. The binary metal doping and composite formation strategies were adopted primarily to facilitate the electronic excitation and accelerate the charge transport characteristics of the finally obtained photocatalyst. Prepared solid samples were characterized by thermogravimetric analysis (TGA), X-ray diffraction (XRD), Raman, Fourier transform-infrared (FT-IR), current-voltage (I–V), BET (Brunauer, Emmett, and Teller), scanning electron microscopy (SEM), and energy-dispersive X-ray (EDX) spectroscopy. An improvement in the photo-degradation of Phenol Red (PR) dye by GCLFO/r-GO nanocomposite was observed. The increased photocatalytic activity of the GCLFO/r-GO nanocomposite is primarily a result of doping, nanotechnology, and composite formation strategies. These strategies tune the bandgap of the nanocomposite sample, increase its surface area, and decrease its electrical resistivity. Highly encouraging photocatalytic findings suggest that using multiple strategies to prepare an ideal photocatalytic material with integrated features is a very efficient approach.     

生物模板法制备金属氧化物及其催化应用研究进展

自然环境中长期进化形成的多层次、多维和多尺度天然硬模板结构和一些具有多层次多维结构的天然“软”生物分子可为多级结构纳米材料的设计与制备提供了新的思路。金属氧化物通常作为催化剂的重要组成部分,其制备与催化应用得到广泛关注,生物模板法为金属氧化物的制备提供了一条简单、绿色、有效的合成路线。本文从基于生物模板的制备方法、生物模板在氧化物制备过程中的作用和生物模板在金属氧化物催化应用时的作用方面总结近十年来的研究进展。基于硬模板的制备方法简单高效,可完美地复制结构类似的金属氧化物材料,而软模板能够灵活地调控金属氧化物颗粒的尺寸和分散性。基于生物模板制备金属氧化物的过程往往经历“吸附-成核-生长-组装”多步骤,生物模板起着表面吸附、空间限域、导向等重要作用。就所得金属氧化物的催化应用而言,生物模板法的优势在于能够实现氧化物材料元素的自掺杂、有效改善传质以及特殊的表面结构赋予催化剂优异的催化性能。     

Fabrication of bifunctional nanocomposite for dye degradation

An effective photocatalytic system is designed to treat with methylene blue. Graphene oxide matrix was decorated with cobalt ferrite and zinc oxide nanoparticles, providing it with dual functionality. The nanocomposite was prepared via sonochemistry. Structural characterization was done by X-ray diffraction. Morphology was observed by scanning electron microscopy while elemental analysis confirmed the purity of the synthesized nanocomposite. The photocatalytic activity of nanocomposite was tested for denaturing methylene blue under solar conditions. Enhanced photocatalytic activity was observed due to trapped electron-hole pairs at graphene oxide surface and other interfaces of the nanocomposite. The efficiency of photocatalyst was calculated as 98% within 15 min which was further examined till 5 more repeated cycles.     

Decoration of carbon cloth by manganese oxides for flexible asymmetric supercapacitors

Here we describe the production of carbon cloth coated with MnO₂ nanosheets or MnOOH nanorods through a normal temperature reaction or a hydrothermal approach, respectively. Of note, the electrochemical performance of MnO₂-coated carbon cloth was better (429.2 F g⁻¹) than that of MnOOH-coated carbon cloth. When the MnO₂-coated carbon cloth is introduced as the positive electrode and the Fe₂O₃-coated carbon cloth as the negative electrode, a flexible asymmetric supercapacitor was obtained with an energy density of 22.8 Wh kg⁻¹ and a power density of 159.4 W kg⁻¹. Therefore, such a hierarchical MnO₂-coated carbon cloth nanocomposite is a promising high-performance electrode for flexible supercapacitors.     

Synergism in methanol synthesis from carbon dioxide over gold catalysts supported on metal oxides

Gold deposited on various oxides with high dispersion was found to be active for the hydrogenation of CO₂ at temperatures between 150 and 400°C. Product selectivities greatly depended on the nature of support oxide. Acidic oxides like TiO₂ gave higher CO₂ conversions but low methanol yields. Zinc oxide component was indispensable for selective methanol synthesis. Significantly, large particle size effect of gold was observed and smaller gold particles gave higher methanol productivity per exposed surface area of gold. This can be explained by an increase in the perimeter area of gold particles with a decrease in particle size. Methanol yield was greatly enhanced in a Au/ZnO---TiO₂ catalyst probably due to an increase in gold-zinc oxide interface.     

Synthesis and characterization of novel Pr6O11/Mn3O4 nanocomposites for electrochemical supercapacitors

This study presents the successful synthesis of praseodymium oxide, Pr₆O₁₁ and hausmannite manganese oxide, Mn₃O₄ nanoparticles, along with a novel synthesis of (Pr₆O₁₁/Mn₃O₄) nanocomposites by employing the hydrothermal route followed by post thermal annealing. X-ray Diffraction, Field Emission Scanning Electron Microscopy and Energy Dispersive X-ray characterization techniques are being adapted to analyze the physical characteristics of all the synthesized materials. XRD results reveal the crystalline nature of the synthesized materials. FE-SEM results display the irregular nanograins of Mn₃O₄ and a regular network of interconnected Pr₆O₁₁ nanoparticles. Nitrogen adsorption/desorption tests confirm the mesoporous nature of all the synthesized electrode materials. The Pr₆O₁₁/Mn₃O₄ ??2 electrode material exhibits an outstanding specific capacitance of 794.58?F/g at a current density of 0.5?A/g, as compared to the 521.24?F/g for the Pr₆O₁₁ electrode material. These investigations provide an easy and efficient method to develop nanocomposites (Pr₆O₁₁/Mn₃O₄) with better electrochemical characteristics, as electrode materials for supercapacitor applications.     

CO_2 methanation over TiO_2–Al_2O_3 binary oxides supported Ru catalysts

TiO_2 modified Al_2O_3 binary oxide was prepared by a wet-impregnation method and used as the support for ruthenium catalyst. The catalytic performance of Ru/TiO_2–Al_2O_3catalyst in CO_2 methanation reaction was investigated. Compared with Ru/Al_2O_3 catalyst, the Ru/TiO_2–Al_2O_3catalytic system exhibited a much higher activity in CO_2 methanation reaction. The reaction rate over Ru/TiO_2–Al_2O_3 was 0.59 mol CO_2·(g Ru)1·h-1, 3.1 times higher than that on Ru/Al_2O_3[0.19 mol CO_2·(gRu)-1·h-1]. The effect of TiO_2 content and TiO_2–Al_2O_3calcination temperature on catalytic performance was addressed. The corresponding structures of each catalyst were characterized by means of H_2-TPR, XRD, and TEM. Results indicated that the averaged particle size of the Ru on TiO_2–Al_2O_3support is 2.8 nm, smaller than that on Al_2O_3 support of 4.3 nm. Therefore, we conclude that the improved activity over Ru/TiO_2–Al_2O_3catalyst is originated from the smaller particle size of ruthenium resulting from a strong interaction between Ru and the rutile-TiO_2 support, which hindered the aggregation of Ru nanoparticles.     

1-Methyl-3-butylimidazolium tetraflouroborate with activated carbon for electrochemical double layer supercapacitors

This article presents the main features of electrochemical double layer supercapacitors, made of nanostructured carbon materials with specially selected and optimized porosity structure and electrolyte based on solvent-free ionic liquid as follows 1-methyl-3-butylimidazolium tetrafluoroborate (1Me3BuImBF₄). The performance of supercapacitor was carried out by cyclic voltammetry and galvanostatic charge/discharge measurements. The main characteristics of stacked supercapacitors exhibit a nominal voltage 3.0 V and a maximum cell voltage 3.5 V as well as a specific capacitance (individual electrode of supercapacitor) of 111 F/g. The specific energy of 4.1 Wh/kg and specific power of 1.7 W/kg for industrial stacked supercapacitor has been achieved.     

Advanced metal oxide (supported) catalysts: Synthesis and applications

A variety of metal oxides catalysts are used in heterogeneous catalysis for chemical processes and have now been developed for their catalytic performance and durability. The heterogeneous catalysis is the most important technology in chemical industry as well as other environmental, energy applications, etc. This review examines recent advances at the preparation and applications of metal oxide particles, especially pertaining to catalytic enhancements for current and future chemical process such as Fischer–Tropsch process, alkylation, and transesterification and environmental applications such as the oxidation of volatile organic compounds and the reduction of NO_x.     

Urchin like NiCo2O4/rGO nanocomposite for high energy asymmetric storage applications

New attractive advances in electrode preparation for supercapacitor applications with rGO based composite materials are eye-catching attention of researchers. Cobalt oxide is considered as an effective electrode for full cell fabrication due to its high specific capacitance. Cost effective solvothermal method was used to prepare pristine Co₃O₄ nanorods, NiCo₂O₄ nanorods and NiCo₂O₄/rGO urchin like nanocilia structure composite materials. The complete electrochemical studies were used to check the obtained product electrochemical activity. The high specific capacitance values are obtained for NiCo₂O₄/rGO urchin like nanocilia composite electrode material which leads to design a full cell and make use as practical applications with illuminating red, green, blue LED source. The capacitive retention of 92.28% even after 5000 cycles achieved in GCD cyclic performance at a high current density implies its excellent stability.