Supercapacitive behaviors of worm-like mesoporous carbon in non-aqueous electrolyte

This paper discusses the electrochemical behaviors of worm-like mesoporous carbon obtained in 1.0 mol L⁻¹ LiClO₄/ethylene carbonate + dimethyl carbonate solution. The capacitance for nanoporous carbon system advances up to 147 F g⁻¹ and a wide voltage window (2.5 V) for three electrode system was achieved. The specific energy and specific power reach as high as 127.6 Wh kg⁻¹ and 5.0 kW kg⁻¹. These results show that worm-like mesoporous carbon can be used for high energy density and power density non-aqueous electrolyte supercapacitors.     

介孔炭CMK-3吸附剂对噻吩类硫化物的吸附性能

研究了采用硬模板法制备的介孔炭CMK-3吸附剂对模拟油中噻吩(TS)、苯并噻吩(BT)及二苯并噻吩(DBT)的吸附性能。采用X射线衍射、氮气吸附-脱附及透射电子显微镜对介孔炭CMK-3吸附剂进行了表征。结果表明,介孔炭CMK-3具有有序的孔道结构,比表面积、平均孔直径和平均孔容分别为1 232 m~2/g、4.878 nm和1.502 cm~3/g。同时探讨了介孔炭CMK-3对TS、BT及DBT的吸附动力学和热力学规律。结果表明,与Freundlich吸附等温模型相比,CMK-3吸附剂对TS、BT及DBT的吸附等温线更符合Langmuir吸附等温模型;吸附为放热过程,CMK-3对TS、BT及DBT的吸附焓变分别为-11.53,-19.74,-26.10 k J/mol。CMK-3吸附剂对TS、BT及DBT的吸附符合二级动力学模型,吸附活化能分别为37.53,34.42,47.67 k J/mol。     

介孔炭CMK-3吸附剂对噻吩类硫化物的吸附性能

研究了采用硬模板法制备的介孔炭CMK-3吸附剂对模拟油中噻吩(TS)、苯并噻吩(BT)及二苯并噻吩(DBT)的吸附性能。采用X射线衍射、氮气吸附-脱附及透射电子显微镜对介孔炭CMK-3吸附剂进行了表征。结果表明,介孔炭CMK-3具有有序的孔道结构,比表面积、平均孔直径和平均孔容分别为1 232 m²/g、4.878 nm和1.502 cm2/g、4.878 nm和1.502 cm³/g。同时探讨了介孔炭CMK-3对TS、BT及DBT的吸附动力学和热力学规律。结果表明,与Freundlich吸附等温模型相比,CMK-3吸附剂对TS、BT及DBT的吸附等温线更符合Langmuir吸附等温模型;吸附为放热过程,CMK-3对TS、BT及DBT的吸附焓变分别为-11.53,-19.74,-26.10 k J/mol。CMK-3吸附剂对TS、BT及DBT的吸附符合二级动力学模型,吸附活化能分别为37.53,34.42,47.67 k J/mol。     

Activation, characterization and hydrogen storage properties of the mesoporous carbon CMK-3

Activation of mesoporous carbon CMK-3 with CO₂ for hydrogen storage was studied. Huge structure and texture changes emerged for the activated CMK-3 based on the characterization by using XRD, TEM and nitrogen adsorption at 77 K. The ordered mesoporous structure of CMK-3 gradually became disorder and its specific surface area and volume of pores especially micropores were enhanced remarkably. Hydrogen sorption measurement showed that the activation led to an obvious increase of the H₂ sorption capacity of CMK-3. The maximum H₂ uptake of 2.27 wt% at 77 K and 1 bar was obtained for the sample activated at 1223 K for 8 h. The small pores with the diameter smaller than 1 nm contributed greatly to the H₂ uptake, and were confirmed more effective than other pores for hydrogen storage.     

Synthesis and characterization of transition metal and metal oxide nanoparticles inside mesoporous carbon CMK-3

Transition metal oxides were synthesized inside the pore system of mesoporous carbon CMK-3. By a wet impregnation, drying and calcination procedure iron, copper, nickel, cobalt, manganese and zinc oxides were formed almost exclusively within the mesopores. A reduction into the metal forms with regard to structural array in the case of zinc oxide and a reduction to manganese(II) oxide for manganese(IV) oxide was accomplished by hydrogen. Powder X-ray diffraction (PXRD), Raman spectroscopy and transmission electron microscopy (TEM) proved the preservation of the host structure during impregnation and reduction procedures. The formation of nanosized metal oxides inside the mesopore system was confirmed with PXRD and TEM. Nitrogen physisorption measurements still revealed micro- and mesoporosity for the host/guest compounds. A reduction of the surface areas and pore sizes in contrast to the host structure being an indication of the coating of the inner surfaces of the carbon walls is shown as well. Infrared and X-ray absorption spectroscopy (XAS) carried out in fluorescence mode confirm the formation of the respective oxides and metals. Furthermore, the existence of small, disordered nanoparticles was proved by XAS investigations and information on the local structure of the metals and metal oxides was obtained from these measurements.     

Improving the electrocapacitive properties of mesoporous CMK-5 carbon with carbon nanotubes and nitrogen doping

Nitrogen-containing carbon composite materials composed of mesoporous carbon CMK-5 and carbon nanotubes (CNTs) were prepared by the chemical vapor deposition method with Fe(NO₃)₃-impregnated SBA-15 as template and pyridine as the carbon precursor. The Fe nanoparticles confined in the channels of SBA-15 induced the formation of mesoporous carbon characteristic of CMK-5, whereas Fe particles homogeneously dispersed on the external surface of SBA-15 served as catalysts for CNTs growth. The contents of CNTs, the N doping level and the microstruture of the carbon composite were closely related to the initial Fe/Si atomic ratio in SBA-15 template. Incorporation of CNTs in the composite was found to substantially reduce the electric resistance, leading to the composite materials exhibiting excellent rate-performance. A maximum specific capacitance of 208 F/g and a power density of 10 kW/kg were achieved in 6.0 mol/L KOH aqueous electrolyte when these carbon composites were applied as supercapacitor electrodes. Moreover, the composite electrode also exhibited good electrochemical stability with no capacitance loss after 1000 cycles of galvanostatic charge-discharge process.     

High sensitive simultaneous determination of catechol and hydroquinone at mesoporous carbon CMK-3 electrode in comparison with multi-walled carbon nanotubes and Vulcan XC-72 carbon electrodes

The simultaneous voltammetric determination of catechol (CC) and hydroquinone (HQ) has been achieved at a mesoporous carbon CMK-3 modified electrode in phosphate buffer solution (pH 7.0). At the electrode both CC and HQ can cause a pair of quasi-reversible and well-defined redox peaks and their peak potential difference increases. In comparison with multi-walled carbon nanotubes (MWCNTs) and Vulcan XC-72 carbon modified electrodes the CMK-3 modified electrode shows larger peak currents and higher adsorbed amounts for the two dihydroxybenzene isomers. This is related to the higher specific surface area of CMK-3. Under the optimized conditions, the linear concentration ranges for CC and HQ are 5 × 10⁻⁷ to 3.5 × 10⁻⁵ M and 1 × 10⁻⁶ to 3 × 10⁻⁵ M, respectively. In the presence of 5 μM isomer, the linear concentration range of CC (or HQ) is 5 × 10⁻⁷ to 2.5 × 10⁻⁵ M (or 5 × 10⁻⁷ to 2.0 × 10⁻⁵ M). The sensitivity for CC or HQ is 41 A M⁻¹ cm⁻² or 52 A M⁻¹ cm⁻², which is close to that without isomer. The detection limits (S/N = 3) for CC and HQ are 1 × 10⁻⁷ M after preconcentration on open circuit for 240 s.     

HEDP溶液体系电沉积铜的电化学行为

采用循环伏安曲线法和阴极极化曲线法研究了0.388 mol/L HEDP(羟基亚乙基二磷酸)+0.160 mol/L Cu SO4·5H2O溶液体系(p H=9.3或9.5)电沉积铜的电极过程动力学规律和添加剂对阴极极化的影响。结果表明,HEDP溶液体系电沉积铜是Cu2+的一步放电还原,遵循无前置化学转化反应或前置化学转化反应很快的不可逆电极过程动力学规律。添加剂HES(含硒无机化合物)和复配添加剂HES+HEA(多胺高分子聚合物)具有促进电沉积铜和抑制析氢的双重作用,提高了HEDP溶液体系电沉积铜的阴极电流效率。     

Magnesiothermal synthesis of nanostructured SiC from natural zeolite (clinoptilolite) and mesoporous carbon CMK-1

Magnesiothermal synthesis of nanosized SiC has been successfully achieved from a mixture of the natural zeolite clinoptilolite and a high-surface area mesoporous carbon CMK-1, synthesized by impregnating a mesoporous silica template MCM-48 with sucrose, followed by carbonization in argon and removal of the silica template. Magnesium powder was used to initiate the self-combustion reaction. Removal of the alkaline and alkaline earth exchangeable cations from the clinoptilolite by ion exchange with NH₄⁺ was essential for a good yield of product, which is also dependent on the use of excess of carbon. TEM confirmed the nanostructure and size of the 15–25 nm SiC product crystallites.     

Calculation of XRD patterns of simulated FDU-15, CMK-5, and CMK-3 carbon structures

XRD patterns of model structures of the ordered mesoporous carbon materials FDU-15, CMK-5, and CMK-3 have been calculated. The structure models had been derived by filling tubular (CMK-5), rod-like (CMK-3), or channel wall (FDU-15) spaces in a given unit cell with carbon atoms. The generated carbon sites then have been used for the calculation of the XRD patterns. It could be shown that XRD patterns of CMK-5 materials vary substantially with variation of the tube diameter and carbon wall thickness. For a certain range of tube diameters, the XRD patterns do not resemble those of CMK-3 or FDU-15. The carbon material FDU-15 is isostructural to the silica SBA-15, CMK-3 is the negative replica of SBA-15. XRD patterns of CMK-3 and FDU-15 models also vary with varying rod or pore diameter but the changes are not as significant as for different CMK-5 models. As expected, the XRD patterns of FDU-15 and CMK-3 resemble each other very much for a given lattice parameter if the rods of CMK-3 are of the same size as the pore diameters of FDU-15.     

Ni- and CuNi-modified activated carbons and ordered mesoporous CMK-3 for furfural hydrotreatment

In this paper, various carbon materials such as activated carbons and mesoporous carbon material CMK-3 modified with nickel and copper, are investigated in the production of a potential biofuel 2-methylfuran with furfural hydrotreatment. Deep characterization of the prepared catalysts revealed differences in pore size, surface area, and metal particle size. Furthermore, the acidity of the catalysts varied significantly affecting the product distribution. Very high activity and selectivity towards 2-methylfuran was achieved with two steam activated carbons (Norit RB4C and Darco) and ordered mesoporous carbon material CMK-3 modified with copper and nickel. 2-Methylfuran yield as high as 60.2% was achieved with 5/5 wt% CuNi/RB4C in 2 h at 230 °C. The operation in slurry phase was observed to promote the reaction towards 2-methylfuran.     

Hydrogen production from catalytic decomposition of methane over ordered mesoporous carbons (CMK-3) and carbide-derived carbon (DUT-19)

This paper presents a thermogravimetric analysis of catalytic methane decomposition using ordered mesoporous carbon nanorods (CMK-3) and ordered mesoporous carbide-derived carbon (DUT-19) as catalysts. X-ray diffraction and N₂ physisorption analyses were performed for both fresh catalysts. Threshold temperatures for methane decomposition with DUT-19 and CMK-3 were estimated by three different methods found in literature. Carbon formation rate and carbon weight gain as a function of time at various temperatures and methane partial pressures were studied, and the kinetics of CMK-3 and DUT-19 as catalysts for methane decomposition were investigated. Arrhenius energy values of 187 kJ/mol for CMK-3 and 196 kJ/mol for DUT-19 with a reaction order of 0.5 were obtained for both catalysts. Results show that carbon deposition on the catalyst during the reaction lead to catalyst deactivation with significant surface modification. Scanning electron microscope studies of fresh and deactivated catalyst samples show the blocking of catalyst pores and the formation of agglomerates on the outer surface of the catalyst during the course of reaction. DUT-19 catalytically outperforms CMK-3 because of a lower threshold temperature, higher surface area, and higher pore volume. These results show that ordered mesoporous carbons are promising catalysts for methane decomposition.     

Detailed structure of the hexagonally packed mesostructured carbon material CMK-3

Detailed investigation of the ordered mesoporous CMK-3 carbon using XRD structural modeling based on the continuous electron density representation and the Rietveld technique allowed deriving comprehensive and consistent information on the material anatomy. The electron density distribution map agrees with carbon ‘bridges’, which seem to be attributed to the material interconnecting carbon nanorods in the CMK-3 mesostructure. These carbon ‘bridges’ are supposed to be derived from former complementary mesopores of the SBA-15 template used.     

Electrochemical behavior of anatase TiO2 in aqueous lithium hydroxide electrolyte

The electrochemical behavior of titanium dioxide (TiO₂) in aqueous lithium hydroxide (LiOH) electrolyte has been investigated. Cyclic voltammetry shows that electroreduction results in the formation of a number of products. X-ray diffraction of the electroreduced TiO₂ shows that Li _x TiO₂, Ti₂O₃, Ti₂O and TiO are formed. The formation of Li _x TiO₂ is confirmed through X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR) studies of the electroreduced TiO₂. The formation of Li _x TiO₂ is electro reversible. In this respect, the electrochemical behavior of TiO₂ in concentrated aqueous lithium hydroxide electrolyte is similar to that for lithium perchlorate (LiClO₄) non-aqueous media.     

Synthesis of CaCO3 nanoparticles by controlled precipitation of saturated carbonate and calcium nitrate aqueous solutions

Calcium carbonate nanoparticles (CCNP) were synthesised by precipitation from saturated sodium carbonate and calcium nitrate aqueous solutions. The effect of agitation rate, mixing time, calcium/carbonate ions concentration and temperature on particle size and morphology were investigated. Particles were characterised using X‐ray diffraction (XRD), transmission electron microscopy (TEM) and thermogravimetric analysis (TGA). Increasing the mixing time from 30 to 180 min resulted in a decrease in particles size. Mixing rate variation between 300 and 14 000 rpm decreased the particle size. Temperature increase favoured a significant growth in particle size and in the formation of aragonite beginning from 80°C. Calcium and carbonate ion concentrations are key parameters controlling the CCNP particle size. Calcite is the main polymorph obtained as revealed by XRD analysis. © 2011 Canadian Society for Chemical Engineering     

Factors contributing to ageing of high voltage carbon/carbon supercapacitors in salt aqueous electrolyte

Accelerated ageing based on floating has been used to investigate the state of health of high voltage carbon/carbon capacitors in aqueous Li₂SO₄ electrolyte and to determine the factors influencing their life-time. A pressure sensor connected to the cell allowed to measure gas evolution caused by overcharging of the system and to determine the maximum operating voltage limit of the cell. At voltage higher than 1.5 V, gases started to evolve, together with oxidation of the positive carbon electrode material and formation of decomposition and/or corrosion products. The positive electrode was found to entail the ageing of the entire system, being covered by twice more surface oxygenated groups than the negative one after 120 h of floating at 1.7 V. The blockage of pore entrances by oxygenated surface functionalities decreases the accessible pore volume, causing a decrease of capacitance and an increase of internal resistance during floating. A drop of capacitive current is observed at voltage higher than 1.2 V on the voltammograms already after 20 h floating at 1.7 V. From the study, it can be concluded that the AC/AC supercapacitors using aqueous Li₂SO₄ with stainless steel current collectors can operate safely up to 1.5 V, which is actually much more than the voltage value of 0.8–1 V reached with aqueous KOH and H₂SO₄ electrolytes.     

炭砖在混合硝酸熔融盐中的腐蚀行为

对6种常用炭砖在两种混合硝酸熔融盐中的腐蚀行为进行了研究,借助金相显微镜观察腐蚀前后试样表面形貌,用X射线衍射仪(XRD)分析腐蚀产物成分,并从炭砖的基本性能出发,对其在混合硝酸熔盐中的腐蚀规律进行了探讨。结果表明,炭砖在空气中的传热性能对其在熔融盐传热系统中的应用十分有利,但使用温度不能超过其起始氧化温度,炭砖的石墨化度、气孔率等都会影响到抗腐蚀性,炭砖在400℃及更低温度下的混合硝酸熔融盐中的腐蚀不属于化学腐蚀,主要是物理性破坏。     

Prediction of carbon dioxide gas hydrate formation conditions in aqueous electrolyte solutions

A methodology for predicting the incipient equilibrium conditions for carbon dioxide gas hydrates in the presence of electrolytes such as NaCl, KCl and CaCl₂ is presented. The method utilizes the statistical thermodynamics model of van der Waals and Platteeuw (1959) to describe the solid hydrate phase. Three different models were examined for the representation of the liquid phase: Chen and Evans (1986), Zuo and Guo (1991), and Aasberg-Petersen et al. (1991). It was found that the model of Zuo and Guo (1991) gave the best results for predicting incipient CO₂ gas hydrate conditions in aqueous single salt solutions. The model was then extended for prediction of CO₂ gas hydrates in mixed salts solutions. The predictions agree very well with experimental data.     

Template synthesis of CMK-3 nanostructured carbon material and study of its properties

Mesostructured carbon has been obtained by template synthesis. SBA-15 mesostructured silicate has been used as a template. The effect of the properties of a template on the ordering of a replica has been studied. It has been shown with the use of X-ray diffraction, gas adsorption, and electron microscopy that there are evident correlations of the conditions of synthesis of a template with the ordering of a carbon replica, which can be guided by the synthesis of materials. The ordering of a replica significantly depends on the mesopore volume of the initial template and thickness of the pore wall. One should use templates with the highest possible mesopore volume and minimal wall thickness to obtain highly ordered replicas. These templates can be prepared during the treatment of synthesized materials at temperatures close to 100°C. It has been determined that, when there is SBA-15, the presence of micropores is a necessary condition for the preparation of carbon replicas that retain the structure of the template.     

Iron (III) oxide nanoparticles within the pore system of mesoporous carbon CMK-1: intra-pore synthesis and characterization

Iron (III) oxide nanoparticles were synthesized inside the pore system of mesoporous carbon CMK-1. This intra-pore synthesis was carried out using several cycles of wet impregnation, drying and calcination procedures. The existence of iron (III) oxide nanoparticles within the pore system was proved by powder X-ray diffraction, nitrogen physisorption, preservation of the host structure by Raman spectroscopy and transmission electron microscopy. Finally, the local structure of the iron oxide was determined by X-ray absorption spectroscopy.