Two-step hydrothermal synthesis of Ru-Sn oxide composites for electrochemical supercapacitors

A two-step hydrothermal process was developed to synthesize hydrous 30RuO₂-70SnO₂ composites with much better capacitive performances than those fabricated through the normal hydrothermal process, co-annealing method, or modified sol-gel procedure. A very high specific capacitance of RuO₂ (C_S,Ru), ca. 1150 F g⁻¹, was obtained when this composite was synthesized via this two-step hydrothermal process with annealing in air at 150 °C for 2 h. The voltammetric currents of this annealed composite were found to be quasi-linearly proportional to the scan rate of CV (up to 500 mV s⁻¹), demonstrating its excellent power property. From Raman, UV-vis spectroscopic and TEM analyses, the reduction in mean particulate size is clearly found for this two-step oxide composite, attributable to the co-precipitation of (Ru_δSn_1−δ)O₂·xH₂O onto partially dissolved SnO₂·xH₂O and the formation of (Ru_δSn_1−δ)O₂·xH₂O crystallites in the second step. This effect significantly promotes the utilization of RuO₂ (i.e., very high C_S,Ru). The excellent capacitive performances, very similar to that of RuO₂·xH₂O, suggest the deposition of RuO₂-enriched (Ru_δSn_1−δ)O₂·xH₂O onto SnO₂·xH₂O seeds as well as the individual formation of (Ru_δSn_1−δ)O₂·xH₂O crystallites in the second hydrothermal step.     

Cathodic electrodeposition of MnOx films for electrochemical supercapacitors

Cathodic electrosynthesis has been utilized for the fabrication of MnO_x films. The use of polyethylenimine (PEI) as an additive enabled the formation of adherent films, which exhibited enhanced resistance to cracking during drying. The polymer content in the deposits can be varied by the variation of the polymer concentration in the solutions. The mechanism of PEI deposition was proposed which is based on the use of PEI-Mn²⁺ complexes. The deposition yield has been studied at different deposition durations. X-ray diffraction analysis showed the crystallization of Mn₃O₄ phase at 300 °C and Mn₂O₃ at 500 °C. The electrochemical performance of the MnO_x films sintered at different temperatures was studied by cyclic voltammetry (CV), chronopotentiometry and impedance spectroscopy in Na₂SO₄ solutions. The films showed excellent pseudocapacitive behavior. The specific capacitance (SC) of 425 F/g in a potential window of 0-0.9 V was obtained from the CV data at a scan rate of 10 mV/s. The SC calculated from the chronopotentiometry data is about 445 F/g. The SC decreased by ∼20% after 1000 cycles. SEM investigations revealed changes in the film morphology during cycling. Obtained results indicate that the proposed method can be used for the fabrication of electrodes for electrochemical supercapacitors.     

“一锅法”水热制备CuS/C复合材料及其在超级电容器中的应用

采用三水合硝酸铜为铜源、硫脲为硫源、D-葡萄糖酸钠为络合剂,发展了简单的“一锅法”水热直接一步合成CuS/C复合材料。采用X射线衍射仪（XRD）、激光显微拉曼光谱仪（Raman）、扫描电子显微镜（SEM）和有机元素分析仪对复合材料组成、结构及形貌进行表征。研究发现,样品主要由花状CuS球组成,同时含有质量分数约为6%的光滑炭球,CuS球表面分布有花瓣状褶皱,形成的大量孔道有利于离子传输,并增大活性物质与电解液的接触面积。研究表明,在1 A·g^-1电流密度下,比电容高达719 F·g^-1,与不加络合剂制备得到的CuS（382 F·g^-1）相比,比电容显著提高,并且在充放电1000次后比电容保持在80%左右,显示出良好的循环稳定性。     

Fabrication of different conductive matrix supported binary metal oxides for supercapacitors applications

Here, we have fabricated the spinel binary-metal oxide (FeCo₂O₄) via a solvent-free and cost-effective approach. The nanocomposites of the as-fabricated binary-metal spinel oxide have been prepared with three different conductive-matrices, namely r-GO, CNTs, and PANI, via ultra-sonication approach. The spinel phase and surface functionalities of the fabricated FeCo₂O₄ sample have been confirmed via XRD and FT-IR analyses, respectively. The morphological-structure and elemental composition of the fabricated samples have been probed via FESEM and EDX results. The role of added conductive-matrices in the improvement of the electrical conductivities of the fabricated nanocomposites has been investigated via I–V experiments. The electrochemical experiments, conducted in half-cell configuration, showed that FeCo₂O₄/PANI nanocomposite exhibited the highest specific capacitance (658.9 Fg^-1) than that of the remaining two nanocomposites. Furthermore, FeCo₂O₄/PANI nanocomposite exhibited excellent cyclic stability as it lost just 8.3% of its initial specific capacitance even after 3000 cyclic tests. The superior capacitive-activity of the FeCo₂O₄/PANI nanocomposite is accredited to its high conductivity, large surface area, and synergy effects between the pseudocapacitance derived from the PANI and FeCo₂O₄ nanostructure. The electrochemical and electrical measurements suggested that FeCo₂O₄/PANI nanostructure is an emerging contender for energy storage applications.     

Direct sintering of UO2+x oxides prepared under hydrothermal conditions

The sintering of uranium oxide powders prepared by hydrothermal conversion of oxalates was studied. A dilatometric study first showed that among the synthesis conditions, only the pH largely impacted the densification, notably through the powders morphology. Three samples (single crystals – pH = 1, microspheres – pH = 2 and nano‑powders – pH = 8) were further selected to study their sintering behaviour. Densitometric and granulometric data then allowed establishing sintering maps. For single crystals and microspheres, densities above 96 %TD were obtained at 1700 °C. In contrast, only 2–8 hours at 1500 °C were needed to yield comparable results for nano-powders. These observations confirm that the hydrothermal conversion of oxalates can be considered as a promising route for the synthesis of actinide oxides, which can subsequently be sintered directly.     

Selective conversion of glucose into lactic acid and acetic acid with copper oxide under hydrothermal conditions

Biomass as a source for chemicals production attracts growing attention due to the decreasing storage of fossil fuels and global warming caused by emission of CO₂. In this study, conversion of glucose with copper oxide (CuO) was studied under alkaline hydrothermal conditions using a batch reactor and continuous flow reactor. CuO, as an oxidant, greatly improves the yields of lactic acid (LA) and acetic acid from glucose and was reduced into Cu₂O and Cu. Selective production of LA with the highest yield of 59% and acetic acid with the highest yield of 32% can be achieved by controlling reaction time, temperature, and addition of CuO. A possible mechanism of conversion of glucose with CuO was proposed. © 2012 American Institute of Chemical Engineers AIChE J, 59: 2096–2104, 2013     

Electrochemical behavior of organic and inorganic complexes of Zn(II) as corrosion inhibitors for mild steel: Solution phase study

This work intends to study inhibitive performance of organic and inorganic complexes of Zn(II) using electrochemical techniques along with surface analysis. In this regard, inorganic zinc aluminum polyphosphate pigment as modified zinc phosphate and zinc acetylacetonate and benzimidazole mixture representing organic replacement of zinc phosphate were employed. Through taking advantage of electrochemical impedance spectroscopy and DC polarization, two mentioned approaches were indicated to be efficient. Charge transfer resistance and corrosion current density values exhibited superiority of zinc aluminum polyphosphate and mixture of zinc acetylacetonate and benzimidazole compared to zinc phosphate and also zinc acetylacetonate and benzimidazole as individual inhibitors. Corrosion inhibition efficiencies calculated based on charge transfer resistance in consistent with those calculated from corrosion current density showed the following sequence; zinc aluminum polyphosphate > mixture of zinc acetylacetonate and benzimidazole > zinc acetylacetonate > zinc phosphate > benzimidazole. Showing film formation, surface analysis SEM/EDX confirmed the results obtained by electrochemical methods.     

Electrochemical and quantum chemical study of purines as corrosion inhibitors for mild steel in 1 M HCl solution

The purines and its derivatives, such as, guanine, adenine, 2,6-diaminopurine, 6-thioguanine and 2,6-dithiopurine, were investigated as corrosion inhibitors for mild steel in 1 M HCl solution by weight loss measurements, electrochemical tests and quantum chemical calculations. The polarization curves of mild steel in the hydrochloric acid solutions of the purines showed that both cathodic and anodic processes of steel corrosion were suppressed. The Nyquist plots of impedance expressed mainly as a depressed capacitive loop with different compounds and concentrations. For all these purines, the inhibition efficiency increased by increasing the inhibitor concentration, and the inhibition efficiency orders are 2,6-dithiopurine > 6-thioguanine > 2,6-diaminopurine > adenine > guanine with the highest inhibiting efficiency of 88.0% for 10⁻³ M 2,6-dithiopurine.The optimized structures of purines, the Mulliken charges, molecular orbital densities and relevant parameters were calculated by quantum chemical calculations. The quantum chemical calculation results inferred that the adsorption belong to physical adsorption, which might arise from the π stacking between the π electron of the purines and the metal surface.     

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.     

Cathodic electrosynthesis of iron oxide films for electrochemical supercapacitors

Cathodic electrosynthesis has been utilized for the fabrication of γ-Fe₂O₃ films, containing chitosan additive as a binder. The films were studied by X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, differential thermal analysis, and thermogravimetric analysis. Cyclic voltammetry and chronopotentiometry data showed that the iron oxide films exhibit electrochemical capacitance in the voltage window of −0.9 to −0.1 V vs SCE in 0.25 m Na₂SO₄ and 0.25 m Na₂S₂O₃ aqueous solutions. The highest specific capacitance (SC) of 210 F g⁻¹ was achieved using 0.25 m Na₂S₂O₃ as electrolyte, at a scan rate of 2 mV s⁻¹. The SC decreased with increasing film thickness, scan rate and cycle number. Heat treatment of the films at 140 °C resulted in increasing SC.     

One-pot synthesis of monoclinic ZrO2 nanocrystals under subcritical hydrothermal conditions

This study reports a one-pot synthesis technique for the preparation of single-phase monoclinic zirconium oxide (ZrO₂) nanocrystals. The products were synthesized from only zirconium oxynitrate (ZrO(NO₃)₂) as the precursor under hydrothermal conditions using subcritical water. The precursor was heat-treated in a batch-type reactor at a reaction temperature of 250 °C for 24 h to obtain pure monoclinic-structured ZrO₂ nanocrystals. The crystallization temperature of the ZrO₂ phase was also greater than 200 °C. However, the products of reactions conducted at 200 °C for 24 h were mixtures of the tetragonal and monoclinic structures. At a reaction temperature of 250 °C, the volume fraction of the monoclinic phase increased; however, the reaction time was also important. The heat-treatment was performed for more than 12 h in order to obtain single-phase monoclinic ZrO₂ nanocrystals. The crystallite size of this product was approximately 20 nm, and water, hydroxide groups, and nitro groups were chemisorbed on its surface.     

Synthesis of monodispersed micaceous iron oxide by the oxidation of iron with oxygen under hydrothermal conditions

The oxidation behavior of iron powder with oxygen was investigated in 5–25 m NaOH solutions at 5 MPa of oxygen partial pressure and 130–290°C, where m = mol(kg H₂O)^?1. Monodispersed micaceous iron oxide, α-Fe₂O₃, was synthesized by the oxidation of iron powder with 5 MPa of oxygen in 10–16 m NaOH solutions at 250–270°C. The diameter of micaceous iron oxide greatly changed depending on the reaction conditions such as the temperature, reaction time and concentrations of NaOH and coexisting ions.     

Electrochemical supercapacitor material based on manganese oxide: preparation and characterization

A novel class of electrochemical supercapacitor electrode material has been electrochemically synthesized from a manganese halide complex in water-containing acetonitrile electrolyte at room temperature. This material has been physically and chemically characterized by scanning electron microscopy, X-ray photoelectron microscopy (XPS), FT-Raman microscopy and cyclic voltammetry. XPS and FT-Raman characterization suggest that this material is composed of manganese oxide with a chemical composition of Mn₃O₄ and containing a moderate amount of carbon. Cyclic voltammetric characterization indicates that this material has higher electronic conductivity than usually seen for manganese oxide and that it shows fast kinetics for the charge-discharge process in both aqueous and acetonitrile electrolytes. The material provides a large pseudocapacitance over a potential window of about 1 V in aqueous electrolyte and about 2 V in acetonitrile electrolyte. It is therefore a good candidate as a material for an electrochemical supercapacitor electrode.     

Hypochlorite production on Ru-Sn binary oxide electrode and its application in treatment of dye wastewater

Ruthenium-tin binary oxides [(Ru+Sn)O₂] were coated on titanium substrates by thermal decomposition. The surface morphologies and elemental analyses of these electrodes were examined by means of scanning electron microscopy. The electrochemical behaviours were characterized by cyclic voltammetry and linear-scan voltammetry (LSV) methods. The effects of electrolysis condition for the current efficiency (CE) of hypochlorite production on binary (Ru+Sn)O₂ electrodes and the treatment of a high salt-containing dye wastewater using this hypochlorite were also investigated. The highest CE for hypochlorite production exists on an RS3 (40 to 80 mol% Sn in coating solution) electrode. The major factors influencing CE for hypochlorite production are the electrolyte flow rate, current density, and chloride (Cl-) concentration. Major factors affecting energy yield are current density, Cl- concentration, and electrode distance. For low current density (300 mA.cm^?2), high Cl- concentration (1 mol.L^?1), and 0.45 cm electrode separation, a high specific energy is obtained. The RS3 electrode exhibits the best removal of organics and chromophor groups in the dye wastewater. On this electrode, better removal of organics and chromophor groups is obtained at 300 mA.cm^?2. The colour of black-red dye wastewater becomes light yellow when a charge of 792 A·min was passed, while the chemical oxygen demand (COD) of this wastewater is decreased from 10500 mg.L^?1 to 1250 mg.L^?1.     

A comprehensive study of indole catalytic hydrodenitrogenation under hydrothermal conditions

This article focuses on the catalytic hydrodenitrogenation (HDN) mechanism of indole under hydrothermal conditions. Formic acid (FA), which is a donor of both gaseous hydrogen and liquid hydrogen, can improve indole conversion and total yield of denitrogenated products. Ru/C showed the highest activity among the catalysts in this study for indole conversion at all temperature conditions with the existence of H₂, and 91.17% indole was converted at 400°C and 60 min. Based on reaction kinetic experiments, a kinetic model was developed mathematically to describe the hydrothermal HDN reaction of indole over the home-made Ni₈₀Ru₂₀/γ-Al₂O₃ catalyst, which clearly captured all data trends and fitted the temporal variation of all major liquid products. High activation energy for the formation of the O-containing substance o-cresol from both mathematical fitting and density functional theory (DFT) calculation indicated the rare occurrence of a reaction between the pyrrole ring-opening product methyl aniline and H₂O, consistent with the experimental observation that only a trace of o-cresol was detected.     

A novel and direct synthesis of thiolesters using cyanuric chloride under mild conditions

A direct synthesis of thiolester from carboxylic acids and thiols under mild conditions using cyanuric chloride as an inexpensive and readily available reagent is described.     

Structural characterization and electrochemical properties of Co<Subscript>3</Subscript>O<Subscript>4</Subscript> anode materials synthesized by a hydrothermal method

Cobalt oxide [Co₃O₄] anode materials were synthesized by a simple hydrothermal process, and the reaction conditions were optimized to provide good electrochemical properties. The effect of various synthetic reaction and heat treatment conditions on the structure and electrochemical properties of Co₃O₄ powder was also studied. Physical characterizations of Co₃O₄ are investigated by X-ray diffraction, scanning electron microscopy, and Brunauer-Emmett-Teller [BET] method. The BET surface area decreased with values at 131.8 m²/g, 76.1 m²/g, and 55.2 m²/g with the increasing calcination temperature at 200°C, 300°C, and 400°C, respectively. The Co₃O₄ particle calcinated at 200°C for 3 h has a higher surface area and uniform particle size distribution which may result in better sites to accommodate Li⁺ and electrical contact and to give a good electrochemical property. The cell composed of Super P as a carbon conductor shows better electrochemical properties than that composed of acetylene black. Among the samples prepared under different reaction conditions, Co₃O₄ prepared at 200°C for 10 h showed a better cycling performance than the other samples. It gave an initial discharge capacity of 1,330 mAh/g, decreased to 779 mAh/g after 10 cycles, and then showed a steady discharge capacity of 606 mAh/g after 60 cycles.     

花状Ni(OH)2的制备及其电化学性能研究

以NiCl₂·6H₂O和NH₃·H₂O为原料,采用简单的水热法,借助表面活性剂CTAB成功合成了β-Ni(OH)₂。研究表明,该材料具有以纳米片相互穿插构成的花状分层微米球结构,比表面积高达45 m²?g^-1。电化学测试表明材料具有良好的电化学性能,在3 A?g^-1的充放电电流密度下,Ni(OH)₂的比容量达到505 C?g^-1,在超级电容器领域具有良好的应用前景。     

添加脂肪族多元醇水热制备空心沸石

以Al2(SO4)3·(14～18)H2O和Na2SiO3·5H2O为主要原料,通过加入一类脂肪族多元醇,用NaOH溶液调整pH值,利用简单的水热法制备了几种微细粉体。经X射线衍射(XRD)测试,其中一种粉体为方沸石和方钠石晶体的复合体,扫描电镜(SEM)照片显示,微细粉体为均一的直径小于5μm的空心球;另外两种都为P型沸石,扫描电镜(SEM)照片显示为空心的八面体,大小约30μm。