Na2SO4 Aqueous Solution Research Articles

Microscale Electrolysis Using Coin-Type Lithium Batteries and Filter Paper

An educational experiment illustrates the electrolysis of water and copper chloride to middle school science students. The electrolysis cell is composed of filter paper soaked with Na2SO4 or CuCl2 aqueous solution sandwiched, along with a sheet of platinum foil, between two coin-type lithium batteries. When the electrolysis is carried out, the electrolysis cell is connected to a current indicator with a light-emitting diode (LED) and to a current-regulating diode (CRD). Because no elaborate components such as an ammeter, dc supply, or Hoffman Cell are needed, the experiment is easy and inexpensive to carry out. In addition, the time needed to obtain the result is less than 5 min and the results are visually clear. The water electrolysis experiment was tried in science classes of ninth grade students, and the responses from the students were positive.

Efficient Electrolyte Additives of Phosphate, Carbonate, and Borate to Improve Redox Capacitor Performance of Manganese Oxide Electrodes

For a faradaic electrochemical capacitor, birnessite-based manganese dioxide electrode, prepared by the electrochemical activation of ball-milled Mn3O4 composite electrodes as we recently reported, delivers 190 F g−1 in a Na2SO4 aqueous solution in the potential range of −0.1 and 0.9 V vs. Ag/AgCl at a current rate of 1.0 A g−1. However, the specific capacitance of birnessite gradually decreases during successive charge and discharge cycle, and the capacity decrease is accompanied by the gradual loss of net weight of manganese oxide because of manganese dissolution from electrode into electrolyte solution. By adding and dissolving small amounts of Na2HPO4, NaHCO3, and Na2B4O7 into the Na2SO4 solution, the capacitance of birnessite increases to 200–230 F g−1 with much improved cyclability over >1000 cycles, resulting from suppression of the manganese dissolution because of pH buffer action by the additives. The improvement of cyclability and capacitance is due to the formation of protection layer on the birnessite and the optimized pH buffer capacity of aqueous electrolyte.

Synthesis of graphene–NiFe2O4 nanocomposites and their electrochemical capacitive behavior

Reduced graphite oxide-NiFe2O4 (RGO-NiFe2O4) composites were synthesized by adding different amounts of NH3 center dot H2O into a mixed aqueous solution of graphite oxide, Ni(NO3)(2) and Fe(NO3)(3) at room temperature. NH3 center dot H2O was used to adjust the synthesis system's pH value. The morphology and the microstructure of the as-prepared composites were characterized by X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) and transmission electron microscope (TEM) techniques. The structure characterizations indicate that NiFe2O4 successfully deposited on the surface of the RGO and the morphologies of RGO-NiFe2O4 show a transparent structure with NiFe2O4 homogeneously distributed on the RGO surfaces. Capacitive properties of the synthesized electrodes were studied using cyclic voltammetry and electrochemical impedance spectroscopy in a three-electrode experimental setup using 1 M Na2SO4 aqueous solution as electrolyte. It is found that the pH value plays an important role in controlling the electrochemical properties of these electrodes. Among the synthesized electrodes, RGO-NiFe10 (pH = 10) shows the best capacitive properties because of its suitable particle size and good dispersion property. It could be anticipated that the synthesized electrodes will gain promising applications as novel electrode materials in supercapacitors and other devices by virtue of their outstanding characteristics of controllable capacitance and facile synthesis.

Hierarchical TiO2 nanobelts@MnO2 ultrathin nanoflakes core–shell array electrode materials for supercapacitors

Hierarchical TiO2 nanobelts@MnO2 ultrathin nanoflakes core–shell arrays (TiO2@MnO2 NBAs) have been fabricated on a Ti foil substrate by hydrothermal approach and further investigated as the electrode for a supercapacitor. Their electrochemical properties were examined using cyclic voltammetry (CV), galvanostatic charge–discharge, and electrochemical impedance spectroscopy (EIS) in a three-electrode cell. The experimental observations clearly show that the fabricated TiO2@MnO2 NBAs electrode possesses superior rate capability and outstanding cycling performance due to its rationally designed nanostructure. A specific capacitance as high as 557.6 F g−1 is obtained at a scan rate of 200 mV s−1 (454.2 F g−1 at a current density of 200 mA g−1) in 1 M Na2SO4 aqueous solution. The energy density and power density measured at 2 A g−1 are 7.5 Wh kg−1 and 1 kW kg−1 respectively, demonstrating its good rate capability. In addition, the composite TiO2@MnO2 NBAs electrode shows excellent long-term cyclic stability. The fabrication method presented here is facile, cost-effective and scalable, which may open a new pathway for real device applications.

RuO2/MnO2 core–shell nanorods for supercapacitors

RuO2/MnO2 NRs as an electrode for supercapacitors show a high electrochemical performance with a specific capacitance of 793 F g−1 (based on MnO2) by cyclic voltammetry (CV) at a scan rate of 2 mV s−1 in 1 M Na2SO4 aqueous solution. A good rate capability with a specific capacitance of 556 F g−1 at a current density of 1 A g−1 and a good cycling stability (20% degradation after 1000 cycles) were also achieved. The enhancement of capacitive behavior can be attributed to the conductive RuO2 template with a series resistance of 0.75 Ω and a charge transfer resistance of 0.75 Ω. The results show that an active material such as a MnO2 hybrid with highly conductive 1D nanowires may greatly improve the electrochemical performance for supercapacitors.

Large scale synthesized sulphonated reduced graphene oxide: a high performance material for electrochemical capacitors

Large scale reduced graphene oxide (RGO) with sulfonic acid groups (SRGO) has been synthesized by a one-step facial method for high performance electrochemical capacitors (ECs). The as-prepared SRGO shows an enhanced specific surface from 254 to 434 m2 g−1 and bulk conductivity from 2 × 10−4 to 2.5 × 10−4 S m compared with that of pristine RGO. An asymmetric EC was assembled with SRGO as the working electrode and Pt as the counter electrode immersed in a 1 M neutral aqueous Na2SO4 solution. The results showed that a maximum specific capacitance of 130 F g−1 was achieved by the SRGO, which is much higher than that of pristine RGO. The SRGO also exhibits a high rate capability and superior cycling stability of more than 99% retention of the specific capacitance after 1000 cycles. Furthermore, it also exhibits excellent specific energy and power densities of 14.6 W h kg−1 and 50 W kg−1 at a current density of 100 mA g−1, respectively. These results suggest that our SRGO material could be a very promising and versatile building block for carbon-based materials as electrodes towards the next generation of high-performance ECs.

A Study on the Influence of Na2SO4 on the Solubility of CO2 in Aqueous Solutions of (N,N-dimethylmethanamide)

Abstract The influence of sodium sulphate on the solubility of carbon dioxide in aqueous solutions of N,N-dimethylmethanamide {= N,N-dimethylformamide, (CH3)2N-C(H)O, DMF} was investigated experimentally at three temperatures (314 K, 354 K, and 395 K). The solvent was an aqueous solution of DMF (mole fraction of DMF in the salt-free solution ≈ 0.05) and sodium sulphate (molality ≈ 0.6 mol·(kgH2O)−1). The maximum pressure of the new experimental gas solubility data reaches nearly 10 MPa. A thermodynamic model that combines two models for the solubility of CO2 (in aqueous solutions of Na2SO4 on one side and in aqueous solutions of DMF on the other side) is used to predict the influence of Na2SO4 on the solubility of CO2 in aqueous solutions of DMF. The new experimental data are compared with such predictions and with calculations from an extension of that model where a single ternary parameter for interactions between the three solutes (i.e., CO2, Na2SO4, and DMF) is adjusted to improve the representation of the experimental data.

Pressure dependence of the Raman spectra of aqueous solutions and anthracene

The shifts of the main bands in the Raman spectra during isothermal pressurization up to 140 MPa for anthracene and 1 M solutions of NaClO4 and Na2WO4 are measured using an optical cell with sapphire windows. The resulting shifts in the maxima of the spectral bands (from 0.6 to 1.1 cm−1 per 100 MPa) are close to the published value for a 1 M Na2SO4 aqueous solution.

Characteristics of Colored Passive Layers on Zirconium: Morphology, Optical Properties, and Corrosion Resistance

Brightly colored and uniform passive layers on Zr can be formed by applying alternating current (ac) voltage (V(ac)) for 10 s in 10 wt % aqueous Na(2)SO(4) solution at T = 298 K. The coloration originating from iridescence can be fine-tuned by adjusting V(ac) in the 10-80 V range. Visible light microscopy analysis shows that different grains reveal two or three different colors due to the polycrystalline nature of Zr, and the resultant coloration is the sum of these contributions. Reflectance spectroscopy spectra show maxima that can be related to the coloration displayed by various grains. Surface morphology and roughness in the micrometer and nanometer ranges are examined using stylus surface profilometry and atomic force microscopy. The formation of colored passive layers on polished Zr makes them smoother but their formation on etched Zr decreases the roughness in the case of low V(ac) and increases in the case of high V(ac). Focused ion beam and scanning electron microscopy are used to determine the thickness (d) of the colored passive layer on etched Zr. It is found that d is in the 51-264 nm range and increases linearly with V(ac). Scanning transmission electron microscopy and electron back scattered diffraction measurements demonstrate that the colored passive layers are uniform and crystalline in nature. Corrosion behavior of the colored passive layers in 1 wt % aqueous NaCl solution is examined using inductively coupled plasma-mass spectrometry. The results indicate that the polished samples hardly undergo any corrosion and the amount of dissolved Zr does not exceed 12 ppb even after exposure for 56 days. On the other hand, the corrosion of the etched samples is ~3 orders of magnitude greater than that of the polished ones, and the amount of dissolved Zr approaches 970 ppb after exposure for 56 days. Corrosion behavior of etched and colored passive layers on Zr in 1 wt % aqueous NaCl solution is also analyzed by recording potentiodynamic polarization curves in the -1.0 to 3.0 V vs RHE range at a scan rate of s = 1 mV s(-1) and at T = 298 K. They have similar shapes but the formation of colored passive layers decreases the current density (j) at any given potential (E), and the thicker the passive layer the greater the reduction in j. The development of colored passive layers on etched Zr increases the corrosion potential (E(corr)) and decreases the corrosion current density (j(corr)).

Characterization of high-temperature oxide films on dysprosium-doped Fe-20Cr alloys by electrochemical techniques

The oxidation properties of Fe-20Cr, Fe-20Cr-0.2Dy and Fe-20Cr-1Dy alloys were studied using gravimetric and electrochemical techniques. The high-temperature oxide films of Dy-doped Fe-20Cr alloys were prepared in air at 900 °C for 24, 48 and 100 h, respectively. The electrochemical experiment was performed by a three-electrode electrochemical cell and in 0.1 mol/L Na2SO4 aqueous solution. Proper models were built for describing electrochemical impedance spectroscopy of the different oxide layers and the spectra were interpreted in terms of a two-layer model of the films. The results revealed that the oxide films of Dy-doped Fe-20Cr alloys became compacter than that of undoped alloys and retained their good protective ability for a relatively long time. With increasing content of Dy, the protection of the oxide films slightly decreased. Mott-Schottky curves indicated that all the oxides were n-type semi-conductors, and the Nd value of oxide film on Fe-20Cr was much larger than that of Dy-doped Fe-20Cr alloys. The results of kinetic curves and SEM were in agreement with electrochemical impedance spectroscopy and Mott-Schottky data.

Current Generation from Na2SO3 and H2SO3 by Using Carbon Fiber Anode

Abstract Current generation from Na2SO3 aqueous solution was found to occur by using PAN-based carbon fibers with heat treatment at 700 °C. Sixty mL of 0.1 M Na2SO3 and 80 mL of 0.5 M H2SO4 were added into the anode cell and cathode cell, respectively, and current generation was performed for 10 h. As a result, the current value increased from background current of 0.04 to 22.3 mA after 5 min. Afterward, the current was almost constant, and decreased a little in the final stage, accompanied by decrease of the amount of Na2SO3. The current efficiency was calculated to be 91%. The mechanism of the current generation is assumed to be described by the equation: SO32− + 2OH− → SO42− + H2O + 2e−. In the current generation using a 30 Ω resistor, the current was 11.3 mA, so that the voltage is calculated to be 0.339 V. The maximum electric power of this cell is calculated to be 3.83 mW. Next, 60 mL of 0.02 M H2SO3 was added to the anode cell, and current generation was performed for 4 h as well as in the case of Na2SO3. As a result, the current was 8.25 mA after 6 min. Afterward, the value linearly decreased, and the value was 3.80 mA after 3 h. The current generation almost finished after 4 h. In this case, the current efficiency was 28%. Furthermore, chemical groups on the surface of carbon fibers with heat treatment were measured by X-ray photoelectron spectroscopy. The element analysis on the surface resulted in: C, 82 atom %; N, 7.2 atom %; and O, 10.9 atom %; the existence of COO, C=O, C–O, C–C, C=C, C–N, and C=N groups was thus suggested.

The influence of the surface finishing on the electrochemical behaviour of austenitic and superaustenitic steels

AbstractThe influence of surface roughness on the pitting potential and the corrosion potential of the DIN W.Nr. 1.4541 and DIN W.Nr 1.4465 stainless steels were examined using electrochemical techniques. Roughness and electrochemical tests were performed on samples with various surface finishing. Electrochemical studies were conducted in an electrochemical cell where steel electrodes were immersed in 0.1 M NaCl and 0.1 M NaCl + 0.1 M Na2SO4 aqueous solutions. We found for both materials when immersed in 0.1 M NaCl aqueous solution lower pitting potential than in 0.1 M NaCl + 0.1 M Na2SO4. The results showed that the electrochemical behaviour of the DIN W.Nr. 1.4465 is better than of DIN W.Nr. 1.4541.

The simple preparation of birnessite-type manganese oxide with flower-like microsphere morphology and its remarkable capacity retention

Birnessite-type manganese oxide with flower-like microsphere morphology and large specific surface area has been prepared by hydrothermal treating a mixture solution of KMnO4 and (NH4)2SO4 at 90°C for 24h. The obtained material is characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy and N2 adsorption–desorption. Results indicate that the birnessite-type manganese oxide shows novel flower-like microsphere morphology and a specific surface area of 280m2g−1, and the flower-like microsphere consists of the thin nano-platelets. Electrochemical characterization indicates that the prepared material exhibits an ideal capacitive behavior with a capacitance value of 278Fg−1 in 1molL−1 Na2SO4 aqueous solution at a scan rate of 5mVs−1. Moreover, the prepared manganese oxide electrode shows excellent cycle stability, and the specific capacitance can maintain 98.6% of the initial one after 5000 cycles.

Performances of high voltage electrochemical capacitor using ball-milled graphite/Mn3O4 composite electrodes

A novel ball-milled graphite/Mn3O4 composite has been prepared directly through the reaction between high-energy ball-milled graphite and potassium permanganate under microwave irradiation. The microstructure and morphology of the composite have been investigated by X-ray diffraction and transmission electron microscopy. Three-electrode investigations show that the ball-milled graphite/Mn3O4 composite has a high potential window (ΔE=1.9V) in 1M Na2SO4 aqueous solution. A symmetric electrochemical capacitor has been built using graphite/Mn3O4 composite with 1M Na2SO4. This system exhibits ideal supercapacitive properties and stable cycle behavior while the cell voltage is set to as high as 1.8V.

Electrophoretic deposition of MnO2-coated carbon nanotubes on a graphite sheet as a flexible electrode for supercapacitors

A flexible electrode was prepared by microwave heating deposition of manganese oxide (MnO2) on carbon nanotubes (CNTs) followed by electrophoretic deposition of the MnO2-coated CNTs on a flexible graphite sheet (FGS). The prepared MnO2-coated CNTs were characterized by scanning and transmission electron microscopy, and X-ray diffraction. A uniformly thin nano-scale MnO2 coating was formed on the surface of the CNTs. The MnO2-coated CNTs–FGS electrode showed highly capacitive behaviour in the 0.5M Na2SO4 aqueous solution, with a specific capacitance of 442.9F/g based on MnO2 at 2mV/s. It exhibited an excellent cycling stability with no more than 1.1% capacitance loss after 1000cycles at 50mV/s.

Synthesis of Ta3N5 Nanotube Arrays Modified with Electrocatalysts for Photoelectrochemical Water Oxidation

Tantalum nitride (Ta3N5) is a promising material for photoelectrochemical (PEC) water oxidation with a narrow band gap (2.1 eV) that can effectively utilize visible light in the solar spectrum. Ta3N5 nanotube (NT) arrays were synthesized on a Ta foil by electrochemical anodization followed by an ammonia treatment at 800 °C. The photocurrent of nanostructured Ta3N5 was over 3 times higher than that of a dense regular Ta3N5 film in 0.1 M Na2SO4 aqueous solution at pH 11. Several electrocatalysts (IrO2 nanoparticles (NPs), Co3O4 NPs, cobalt phosphate, and Pt NPs) were used to modify Ta3N5 NTs for PEC water oxidation. The photocurrent of Ta3N5 NTs modified with IrO2 and Co3O4 was ca. four times higher than that of unmodified NTs. Cobalt phosphate also showed a positive improvement for PEC water oxidation on Ta3N5 NTs, whereas Pt was ineffective. Scanning electrochemical microscopy was used to measure the faradaic efficiency of the Ta3N5 photoanodes for water oxidation, which can reach as high as 88% for a Co3O4–Ta3N5 NTs photoanode, but is less than 15% at best, for Ta3N5 without the electrocatalyst. The results indicate that cobalt oxide and cobalt phosphate are promising candidates as electrocatalysts on Ta3N5 for water oxidation because Co is an earth-abundant material.

Enhancement of electrochemical capacitive properties based on complementation of morphologies

Manganese dioxides octahedral molecular sieve nanowires with 2×2 tunnels (designated OMS-2) and amorphous manganese dioxides were synthesized via a hydrothermal treatment and a sol–gel method, respectively. Amorphous MnO2 nanoparticles were incorporated into the matrix of OMS-2 nanowires to form homogenous nanocomposites. The structures and morphologies of as-synthesized OMS-2 nanowires and amorphous MnO2 nanoparticles were characterized using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM) and transmission electron microscopy (TEM). Electrochemical behaviors of the as-prepared nanocomposites with varying ratios were investigated by cyclic voltammetry (CV), galvanostatic charge/discharge and potentiostatic electrochemical impedance spectroscopy (EIS) using a three-electrode system in a 0.5M Na2SO4 aqueous solution. Pure OMS nanowires exhibit a specific capacitance of about 37Fg−1, and amorphous MnO2 nanoparticles demonstrate relatively higher specific capacitance of about 106Fg−1 at a scan rate of 2mVs−1. The enhancement of specific capacitance can be carried out by mixing OMS-2 nanowires and amorphous MnO2 nanoparticles to form nanocomposites and the optimized mole ratio of OMS-2 nanowires to amorphous MnO2 as 1:5 can be achieved. The improved specific capacitance can be attributed to the increase of electrode conductivity and the effective interfaces between MnO2 active materials and electrolyte.

Surface Structures of NaF and Na2SO4 Aqueous Solutions: Specific Effects of Hard Ions on Surface Vibrational Spectra

We elucidated surface structure and sum frequency generation (SFG) spectra of aqueous NaF and Na2SO4 solutions by molecular dynamics (MD) simulation. These electrolyte solutions contain hard ions, and their surfaces are considered to be void of ion species. Nevertheless, the two solutions have shown remarkably different SFG spectra, implying different surface structure. The present MD analysis confirmed that all the ionic species are repelled from the surface, though their experimental SFG spectra are well reproduced. The difference in their surface structure is observed in the subsurface region, where slight charge separation occurs in the Na2SO4 solution. The perturbation in the SFG spectra is not attributed to the topmost layer but to the water orientation in a fairly deep region of the surface.

Tin oxide coating on molybdenum oxide nanowires for high performance supercapacitor devices

Tin oxide coated molybdenum oxide nanowires (SnO2/MoO3) are synthesized by a combination of hydrothermal and wet chemical routes. The electrochemical capacitance properties of the SnO2/MoO3 core shell composite nanowires are measured by cyclic voltammetry (CV) and galvanostatic charge–discharge method in 1M Na2SO4 aqueous solutions. The results showed that specific capacitance of SnO2/MoO3 core shell composite nanowires is 295Fg−1, which is much higher than the specific capacitance of pure individual MoO3 (69Fg−1) and SnO2 (96.6Fg−1). Moreover the synthesized core shell composite nanowires has also exhibited excellent long-term cycling stability (only 3% loss of its initial specific capacitance after 1000 cycles) which may lead to its multifarious usage in high-performance energy storage devices for future potential applications.

Novel composite membranes prepared by interfacial polymerization on polypropylene fiber supports pretreated by ozone-induced polymerization

Interfacial polymerization (IP) is a powerful technique for the fabrication of thin film composite (TFC) membranes. In this work, porous polypropylene fiber films were used as a support to fabricate TFC nanofiltration membrane using IP technique. Firstly, the surface of polypropylene fiber film was hydrophilized by introducing peroxide onto the membrane surface using ozone treatment followed by grafting acrylamide. And then interfacial polymerization could be successfully proceeding on the hydrophilized PP membrane. The monomeric system chosen for IP was m-phenylenediamine (MPDA) and trimesoyl chloride (TMC). The ozone treatment time was investigated, and in the range of 5–10min ozone treatment time, the PP fiber membrane had an available amount of peroxides for grafting while keeping the mechanical strength. The characteristics of the original membrane, grafted membrane and TFC membrane were studied with various analytical methods, such as SEM and FTIR-ATR. Meanwhile, the nanofiltration performance was evaluated with aqueous solutions of Na2SO4 (2g/L) and Fast Green FCF (MW 808.84, 10mg/L). The rejection rate of 60% and 90% were achieved for Na2SO4 and Fast Green FCF, respectively, at a transmembrane pressure of 0.5MPa.