Na2SO4 Aqueous Solution Research Articles

Manganese oxide nanowires wrapped with nitrogen doped carbon layers for high performance supercapacitors

In this study, manganese oxide nanowires wrapped by nitrogen-doped carbon layers (MnOx@NCs) were prepared by carbonization of poly(o-phenylenediamine) layer coated onto MnO2 nanowires for high performance supercapacitors. The component and structure of the MnOx@NCs were controlled through carbonization procedure under different temperatures. Results demonstrated that this composite combined the high conductivity and high specific surface area of nitrogen-doped carbon layers with the high pseudo-capacitance of manganese oxide nanowires. The as-prepared MnOx@NCs exhibited superior capacitive properties in 1M Na2SO4 aqueous solution, such as high conductivity (4.167×10−3Scm−1), high specific capacitance (269Fg−1 at 10mVs−1) and long cycle life (134Fg−1 after 1200 cycles at a scan rate of 50mVs−1). It is reckoned that the present novel hybrid nanowires can serve as a promising electrode material for supercapacitors and other electrochemical devices.

Facile synthesis of functionalized porous carbon with three-dimensional interconnected pore structure for high volumetric performance supercapacitors

Functionalized porous carbon with three-dimensional (3D) interconnected pore structure has been successfully synthesized through direct heat-treatment of KOH-soaked soybeans. Benefiting from heteroatoms (N, O) doping, interconnected porous carbon framework with high surface area as well as high packing density (up to 1.1gcm−3), the as-obtained porous carbon material exhibits high volumetric capacitance of 468Fcm−3, good rate capability and excellent cycling stability (91% of capacitance retention after 10,000 cycles) in 6M KOH electolyte. More importantly, the as-assembled symmetric supercapacitor delivers high volumetric energy density of 28.6WhL−1 in 1M Na2SO4 aqueous solution.

Friction and wear behaviour of selected titanium and zirconium based nitride coatings in Na2SO4 aqueous solution under low contact pressure

The low contact pressure friction and wear behaviour of four titanium and zirconium-based nitride coatings were investigated in Na2SO4 electrolyte. The experiments were performed using two different potentiostatic conditions, namely OCP and 0.5V. For all selected potentials, zirconium-based nitride coatings showed an enhanced wear resistance, when compared to titanium-based coatings. This improved wear performance is due to the formation of stable oxide layers for the selected loading conditions, resulting in low and steady friction. Alternatively, titanium-based coatings were more prone to wear accelerated corrosion, which yielded a high and unstable coefficient of friction accompanied by significantly higher wear.

Effect of surfactant on the electrochemical performance of graphene/iron oxide electrode for supercapacitor

In this study, reduced graphene oxide- Fe3O4 (RGO-Fe3O4) nanocomposite is fabricated using simple electrophoretic deposition (EPD) method followed by an electrochemical reduction process. It is characterized using atomic force microscopy, X-ray diffraction, X-ray photoelectron spectroscopy, Raman spectroscopy and scanning electron microscopy. Fe3O4 nanoparticles with 20–50 nm in diameter are uniformly formed on RGO. Electrochemical properties of nanocomposite are characterized by cyclic voltammetery, galvanostatic charge/discharge and electrochemical impedance spectroscopy. According to the galvanostatic charge/discharge analysis, RGO-Fe3O4/SS presents specific capacitance (Cs) of 154 F g−1 at current density of 1 A g−1, which is higher than that of RGO/SS (81 F g−1) in Na2SO4 electrolyte. Also, the electrochemical behaviors show that addition of three kind of surfactant, i.e. sodium dodecyl sulphate, cetyltrimethylammonium bromide, t-octyl phenoxy polyethoxyethanol (Triton X-100) to Na2SO4 aqueous solution can improve the Cs of RGO-Fe3O4/SS electrodes. RGO-Fe3O4/SS in Na2SO4 electrolyte containing Triton X-100 shows maximum Cs of 236 F g−1 at 1 A g−1 which retains 97% of initial capacitance after 500 cycles.

Preparation and characterization of CeO2 decorated TiO2 nanotube arrays photoelectrode and its enhanced photoelectrocatalytic efficiency for degradation of methyl orange

The highly oriented CeO2/TiO2 nanotube arrays (CeO2/TiO2 NTAs) were fabricated by the electrodeposition of CeO2 in 1.0 mol/L Na2SO4 aqueous solution on TiO2 NTAs. CeO2/TiO2 NTAs were characterized by SEM, TEM, XRD, XPS. Its ultraviolet–visible absorption and photoelectrochemical properties were investigated. The degradation of methyl orange was used to evaluate the photoelectrocatalytic activity of CeO2/TiO2 NTAs. The results showed that the CeO2 nanoparticles with a homogenous spherical size of about 15 nm were uniformly deposited onto the surface of TiO2 NTAs. The CeO2 composed with Ce4+ and Ce3+ ions could be observed. CeO2/TiO2 NTAs exhibited a stronger UV and visible light absorptions with 40 nm red-shift of the absorption edge compared with TiO2 NTAs. The separation efficiency of the photogenerated charge carriers of CeO2/TiO2 NTAs can significantly enhanced by the CeO2 deposited. The removal efficiencies (98.1 %) of methyl orange at the CeO2/TiO2 NTAs photoelectrodes was larger than that of the bare TiO2 nanotube arrays photoelectrode (78.1 %).

Photoelectrochemical cell based on n-CuIn5S8 film as photoanodes for photocatalytic water splitting

In this paper, photoelectrochemical cell has been developed using indium tin oxide (ITO) as the substrate of the CuIn5S8 photoanode and Pt as the cathode. The photoresponse measurements have been conducted in neutral Na2SO4 aqueous electrolyte solutions in three-electrode system and under irradiation of 100 mWcm−2. We have found that the [Cu]/[In] molar ratio has strongly influenced the current voltage (J–V) response. The highest photocurrent density of ca. 8 mA/cm2 with an applied potential of 0.25 V vs. Ag/AgCl has been observed for sample deposited from the molar ratio of ([Cu]/[In] = 0.28). The results show that ternary n-CuIn5S8 thin film electrodes have potential in photocatalytic water splitting application.

Preparation and Photoelectrochemical Properties of Multilayered WS2 Coated Titanium Dioxide Nanocomposites

Since TiO2 was discovered for water-splitting to generate hydrogen under UV light, plenty of techniques have been explored to obtain suitable sensitizers for visible-light adsorption in order to increase the activity of water-splitting reaction for hydrogen generation [1-3]. Among them, dispersing a 2D graphene andsimilar layered material on TiO2 nanoparticle exhibits highly photocatalytic activities (i.e. MoS2) [2]. In this paper, graphene-liked WS2 was chosen due to its activity as HER (hydrogen evolution reaction) catalyst and relatively abundant storage [4]. The expected composite was formed through high energy ball milling technique which makes WS2 disperse on the surface of TiO2nanoparticles [5]. The composites consist of 99.5% TiO2 and 0.5% WS2and were prepared by high energy ball milling for five different periods of time-2hours, 4hours, 8hours, 16hours and 32hours. To identify phase evolution of the as-prepared nanocomposites during high energy ball milling procedure, X-ray diffraction (XRD) was performed to examine phase transition, which is shown in Fig.1. It can be seen that, with increasing milling time, the crystallization decrease at first and increase after further milling. To further study the photoelectrochemical (PEC) characterization of composites after ball milling, a three-electrode setup was used, which is shown in inset of Fig. 2. This three-electrode device consists of a reference electrode (Ag/AgCl), a Pt wire counter electrode, a quartz container filled of 0.5M Na2SO4 aqueous solution and a working electrode. Sintered composites on indium-tin-oxide (ITO) glass substrate acts as the working electrode. Fig.2 shows the PEC measurement results of pure TiO2 and milled composites with milling time for 2hours, 8hours and 32hours. As can be seen, composite reaches the best photocurrent response with 8 hours milling. It is obvious that compared to pure TiO2 sample, adding of WS2and high energy ball milling make positive effect to composites. In summary, the structure of TiO2 and WS2 nanocomposites through high energy ball milling has been studied by X-ray diffraction. Photoelectrochemical properties of the TiO2 coated with few layered WS2 shows the optimization photochemical response for 8 hours milled nanocomposites. This work provides a facile and low cost process for large amount production of few layer doped TiO2nanocomposites.

Fabrication of ordered mesoporous carbons anchored with MnO nanoparticles through dual-templating approach for supercapacitors

Ordered mesoporous carbons anchored with MnO nanoparticles (Cs–Mn) for supercapacitor have been produced by a simple double-template strategy. Pluronic F127 and polyurethane (PU) foam are used as the soft and hard template, respectively, and phenolic resol as a carbon source, and the MnO nanoparticles were in-situ anchored by directly dissolved solid Mn(CH3COO)2⋅2H2O in the phenolic resol solution through evaporation induced self-assembly (EISA) of the mesostructure on the struts of the PU foam scaffold, followed by carbonization. The microstructure, morphology and electrochemical performance of Cs–Mn were investigated by small angle X-ray scattering, transmission electron microscopy, Raman spectropy, nitrogen adsorption–desorption and electrochemical measurements. Results show that Cs–Mn have a hexagonally ordered mesostructure. The pore size of Cs–Mn centered at ca. 2.0–4.2nm, high specific surface area (222m2/g) and great pore volume (up to 0.14cm3/g). The electrochemical measurements show that the Cs–Mn as an electrical double-layer capacitor electrode presents high specific capacitance of 100F/g at a current density of 0.125A/g and excellent rate capability using 0.5M Na2SO4 aqueous solution.

Experimental studies and modeling of CO2 solubility in high temperature aqueous CaCl2, MgCl2, Na2SO4, and KCl solutions

The phase equilibria of CO2 and aqueous electrolyte solutions are important to various chemical‐, petroleum‐, and environmental‐related technical applications. CO2 solubility in aqueous CaCl2, MgCl2, Na2SO4, and KCl solutions at a pressure of 15 MPa, the temperatures from 323 to 423 K, and the ionic strength from 1 to 6 mol kg−1 were measured. Based on the measured experimental CO2 solubility, the previous developed fugacity‐activity thermodynamic model for the CO2‐NaCl‐H2O system was extended to account for the effects of different salt species on CO2 solubility in aqueous solutions at temperatures up to 523 K, pressures up to 150 MPa, and salt concentrations up to saturation. Comparisons of different models against literature data reveal a clear improvement of the proposed PSUCO2 model in predicting CO2 solubility in aqueous salt solutions. © 2015 American Institute of Chemical Engineers AIChE J, 61: 2286–2297, 2015

Controlled Construction of Hierarchical Nanocomposites Consisting of MnO2 and PEDOT for High‐Performance Supercapacitor Applications

AbstractThe integration of hierarchical nanostructure design and encapsulation strategies using a combination of electrochemical deposition, hydrothermal, and in situ reaction methods has been recognized as one of the most effective strategies to realize practical applications of various supercapacitor materials. Herein, a facile and scalable method is developed to synthesize a core–shell–branch hierarchical MnO2@PEDOT@MnO2 composite by using a simple electrochemical deposition strategy. The proposed synthesis method facilitates the structural integration of three‐dimensional nickel foam and the synergy of different electroactive materials, which offers several advantages including simplicity, efficiency, no binder, and low cost. The as‐prepared, freestanding, hierarchical MnO2@PEDOT@MnO2 electrodes exhibit high specific capacitance and rate capability. An asymmetric supercapacitor is fabricated with the hierarchical MnO2@PEDOT@MnO2 nanocomposite as the positive electrode, activated carbon as the negative electrode, and Na2SO4 aqueous solution as the electrolyte. The asymmetric supercapacitor can be cycled reversibly in a high‐voltage window of 0–1.8 V and exhibits a high energy density of 47.8 Wh kg−1 at a power density of 180 W kg−1, indicating remarkable rate capability as well as reasonable cycling performance with 91.3 % retention after 5000 cycles.

Synthesis and characterization of VO2(B)/graphene nanocomposite for supercapacitors

A hydrothermal method assisted with freeze drying process was adopted to form composite supercapacitor materials of metastable vanadium dioxide [VO2(B)] nanobelts on reduced graphene oxide (RG) layers. The VO2(B) nanobelts were well dispersed on the graphene layers as verified by scanning electron microscopy and high-resolution transmission electron microscope. Cyclic voltammetry and galvanostatic charge–discharge measurements were adopted to investigate the electrochemical properties of VO2(B)/RG composites in 1.0 M Na2SO4 aqueous solution. The VO2(B)/RG composites delivered better specific capacitance and superior rate capability in comparison with the pure VO2(B). The initial specific capacitance of the composites reached 290.4 F g−1 at 0.2 A g−1 and maintained 82.3 % of the initial value after 1000 cycles at 2 A g−1, 37.9 % higher than the pure VO2(B). Therefore, our results suggest that graphene greatly enhances the electrochemical performance of VO2(B) and VO2(B)/RG composite is a potential material for supercapacitor.

Assessments of Surface Coverage after Nanomaterials are Drop Cast onto Electrodes for Electroanalytical Applications

AbstractThe drop‐casting method for the suspension of nanomaterials on conducting surfaces is a commonly used procedure for evaluating the electrochemical properties of the drop‐cast materials. In this study, we pinpoint a key limitation of the method, which may lead to misinterpretation of the obtained data, especially when evaluating heterogeneous electron‐transfer rates. The electrochemical responses recorded at 1 mm‐diameter copper electrodes modified with porous layers of drop‐cast multiwalled carbon nanotubes (MWCNTs) in 0.1 M Na2SO4 aqueous solutions were examined. Standard amounts of the MWCNTs that are typically used for the drop‐casting procedure (1 mg MWCNT in 1 mL of dimethylformamide) were deposited drop wise on the surface of the copper electrodes. Layers of MWCNTs were progressively built up on the electrode surface by varying the number of drops from 0 to 10. The ability of the MWCNTs to cover and prevent diffusion to the base copper electrode was assessed by performing oxidative cyclic (CV) and linear‐sweep voltammetry (LSV) experiments in the presence of aggressive SO42− supporting electrolyte, where a large oxidative current indicated the occurrence of corroding copper metal. It was demonstrated that a total of 10 drops of the coating solution (equivalent to 640 μg cm−2 of MWCNTs per unit area) was still insufficient in providing complete coverage over the underlying electrode surface (as a corrosion current was still observed), even though considerably lower CNT loadings have been applied in many literature reports. The electrochemical results indicate that, for experiments that utilize the drop‐casting procedure to modify electrode surfaces, it cannot be assumed that the base electrode, nor the pore structure of the coating material, does not significantly contribute to the overall observed voltammetric response.

Construction of cellulose based ZnO nanocomposite films with antibacterial properties through one-step coagulation.

Cellulose based ZnO nanocomposite (RCZ) films were prepared from cellulose carbamate-NaOH/ZnO solutions through one-step coagulation in Na2SO4 aqueous solutions. The structure and properties of RCZ films were characterized using XRD, FTIR, XPS, SEM, TEM, TG, tensile testing, and antibacterial activity tests. The content of ZnO in RCZ films was obtained in the range of 2.7-15.1 wt %. ZnO nanoparticles with a hexagonal wurtzite structure agglomerated into large particles, which firmly embedded in the cellulose matrix. RCZ films displayed good mechanical properties and high thermal stability. Moreover, the films exhibited excellent UV-blocking properties and antibacterial activities against Staphylococcus aureus and Escherichia coli. A dramatic reduction in viable bacteria was observed within 3 h of exposure, while all of the bacteria were killed within 6 h. This work provided a novel and simple pathway for the preparation of regenerated cellulose films with ZnO nanoparticles for application as functional biomaterials.

Nano-iron oxide (Fe2O3)/three-dimensional graphene aerogel composite as supercapacitor electrode materials with extremely wide working potential window

The composite of nano-iron oxide (Fe2O3)/three-dimensional graphene aerogel (Fe2O3/GA) was synthesized by a hydrothermal method. The structural and morphological properties of Fe2O3/GA were characterized through X-ray diffraction and scanning electron microscopy. Fe2O3 particles with 30–60nm in size were homogenously encapsulated in graphene aerogel(GA). In the three-electrode system, an extremely wide working potential window was observed from −0.8 to 0.8V(vs. SCE) in 0.5M Na2SO4 aqueous solution, and a specific capacitance of 81.3Fg−1 was obtained at a constant current density of 1Ag−1.

Controlled Synthesis of Monodispersed Sub‐50 nm Nanoporous In2O3 Spheres and Their Photoelectrochemical Performance

AbstractUniform nanoporous In2O3 nanospheres with high surface areas were synthesized through a simple solvothermal route with ethylenediamine (en) as the solvent. The prepared In2O3 nanospheres with diameters about 50 nm are composed of many nanoparticles with average sizes of ca. 5 nm. The unique nanospheres inherit both the large surface areas of the nanoparticles and the high crystallinity of bulky materials. The introduction of water or some other solvents into the reaction solution results in the formation of InOOH and In(OH)3 particles indicating that en is indispensable for synthesis of In2O3 with a nanoporous nanosphere structure. UV/Vis spectroscopy reveals that the band‐gap of synthesized In2O3 nanospheres is about 2.95 eV, mostly close to that of the single‐crystalline bcc‐In2O3. The PL spectrum of the In2O3 nanospheres shows two emission peaks located at 470 nm and 483 nm. The photocurrent of the prepared In2O3 electrodes by electrophoretic deposition strongly depends on the calcination temperature. The highest photocurrent density up to 1.9 mA cm–2 at 0.65 V (vs. Ag/AgCl) in 0.1 M Na2SO4 aqueous solution was recorded in the sample annealed at 550 °C. The high photocatalytic activity of the In2O3 nanospheres can be attributed to the high surface area, and the large number of nanopores in the In2O3 nanospheres.

One-Step Electrodeposition Process To Fabricate Corrosion-Resistant Superhydrophobic Surface on Magnesium Alloy

A simple, one-step method has been developed to construct a superhydrophobic surface by electrodepositing Mg-Mn-Ce magnesium plate in an ethanol solution containing cerium nitrate hexahydrate and myristic acid. Scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy were employed to characterize the surfaces. The shortest electrodeposition time to obtain a superhydrophobic surface was about 1 min, and the as-prepared superhydrophobic surfaces had a maximum contact angle of 159.8° and a sliding angle of less than 2°. Potentiodynamic polarization and electrochemical impedance spectroscopy measurements demonstrated that the superhydrophobic surface greatly improved the corrosion properties of magnesium alloy in 3.5 wt % aqueous solutions of NaCl, Na2SO4, NaClO3, and NaNO3. Besides, the chemical stability and mechanical durability of the as-prepared superhydrophobic surface were also examined. The presented method is rapid, low-cost, and environmentally friendly and thus should be of significant value for the industrial fabrication of anticorrosive superhydrophobic surfaces and should have a promising future in expanding the applications of magnesium alloys.

An Investigation on the Degradation Behavior of an Asymmetric Supercapacitor of α-MnO2//AC

We have investigated the degradation behavior of a typical asymmetric supercapacitor cell operating in an aqueous solution of Na2SO4 with a voltage window of 2 V, where α-MnO2 and activated carbon (AC) were chosen as the active materials for positive and negative electrodes, respectively. In this study, potentials of α-MnO2 and AC electrodes of the asymmetric cell were monitored with respect to an Ag/AgCl reference electrode during repetitive charge/discharge cycling. Since the charges passed at positive and negative electrodes are the same, a change in a certain parameter should be compensated by changes in the other parameters. An irreversible current due to reduction of water on AC electrode triggered capacitance fade in the initial charge/discharge cycling. This phenomenon made the lowest potential more positive to be deviated from the potential region where water reduction can occur, resulting in the following stable operation. Then, α-MnO2 facilitated the oxidation of water, which deactivated α-MnO2 itself probably due to an irreversible increase in reduced Mn sites. The deactivation of α-MnO2 was compensated by expansion of its potential window in the cathodic scan, leading to further capacitance fade due to dissolution.

Heat transport across a gold nanowire/water interface enhanced by the solution ionic strength

ABSTRACTLithographically fabricated gold nanowires are optically excited with 532nm CW laser and the local temperature change is measured in air, pure water and various concentration aqueous solutions of ionic solutes NaCl, Na2SO4 and MgSO4 using the thermal sensor film of Al0.94Ga0.06N embedded with Er3+ ions. The interface thermal resistance for heat transfer from the excited nanowires into the surrounding liquid is determined from the slopes of the temperature change versus laser intensity plots obtained for the nanowire excitation under various solutions. Addition of ionic solute molecules into the solution decreases the interface thermal resistance and hence leads to increased heat dissipation into the surrounding liquid. Interface thermal resistance decreases exponentially with the ionic strength of solution and saturates around zero for solution ionic strength of 0.3M and higher.

Facile synthesis of α-MnO2 nanowires/spherical activated carbon composite for supercapacitor application in aqueous neutral electrolyte

One-dimensional (1-D) α-MnO2 nanowires/spherical activated carbon composite, namely the α-MnO2 nanowires growth onto the surface of activated mesocarbon microbeads (a-MCMB), has been prepared by using a simple hydrothermal synthesis method. The α-MnO2 nanowires are found to be less than 50 nm in diameter and have a characteristic length up to 2 μm. The novel α-MnO2 nanowires/a-MCMB composite when used for supercapacitor electrode material exhibits a specific capacitance (C s) of 357 F g−1 in 1 M Na2SO4 aqueous neutral solution. The C s based on the α-MnO2 nanowires is estimated to be as high as 890 F g−1. A good cycling stability of this composite material is also demonstrated for supercapacitor application.

Electrolyte Pressure Influence on the Speed of Steel 110G13L Electrochemical Dissolution during Electrochemical Jet Machining

An experimental investigation of an electrochemical dissolution of steel 110G13L (steel of Hadfield) in NaNO3, Na2SO4, and NaCl aqueous solutions was carried out. It has been found that the electrochemical dissolution of steel 110G13L in NaNO3, Na2SO4 aqueous solutions occurs in the active state when φ = 4.5 V. Based on the results of the polarization analysis and determination of the steel 110G13L dissolution depth in each of these solutions, the rational electrolyte composition was chosen for ECJM. The technologic experiment has shown that an increase in the electrolyte feeding pressure up to two МPа leads to a machining depth increase up to 600 μm.