This article summarizes our research on solid electrolytes for rechargeable aqueous lithium-air batteries. Aqueous lithium-air batteries have potential application as a power source for electric vehicles, because of their high specific energy density. A water-stable lithium ion conducting solid electrolyte is the key material for lithium-air batteries to use lithium metal in aqueous circumstance. In this article, two types of lithium ion conducting solid electrolytes, NASICON-type Li1+xAxTi2−x−yGey(PO4)3 (A = Al, Fe) and garnet-type Li7−xLa3Zr2−xAxO12 (A = Nb, Ta) are introduced, and the conductivity behavior of these solid electrolytes by elemental substitution, their chemical stabilities in water and electrochemical stabilities with lithium metal are discussed. Lithium ion conductivities of 1.3 × 10−3 and 5.2 × 10−4 S cm−1 at 25°C were observed in Li1.4Al0.4Ti1.4Ge0.2(PO4)3 and Li6.75La3Zr1.75Ta0.25O12, respectively. These solid electrolytes are unstable in water, but stable in saturated LiOH with saturated LiCl aqueous solution. The former solid electrolyte is unstable in contact with lithium metal, while the latter electrolyte shows stability against lithium metal.
We first report an AlCl3-containing diglyme electrolyte for room temperature Al electrodeposition, which have relatively low volatilities and low cost. With the molar ratio of AlCl3:diglyme = 1:5, the diglyme solution enabled deposition and dissolution of Al, which required relatively small overpotentials at room temperature. The deposits were not dendritic, indicating potential applications for Al plating or Al ion batteries.
Nanocarbon films formed by using unbalanced magnetron sputtering equipment were employed to detect Cd and Pb using anodic stripping voltammetry. The electrode performance was evaluated in acetate and citrate buffers. The Cd-acetate complex was easily reduced because the complexation constant was moderate. This is quite different from the Cd-EDTA complex which cannot be deposited onto an electrode. In contrast, citrate buffer at lower pH is suitable for detecting Pb ion due to weak interaction between Pb2+ and citrate anion. As a result, acetate buffer (pH 5.0) and citrate buffer (pH 2.0) are the optimum solutions for determining Cd and Pb, respectively. Detection limits of 0.5 ng/mL (0.004 µmol dm−3) and 5 ng/mL (0.02 µmol dm−3) were obtained for Cd and Pb ions, respectively. These detection limits are about one order of magnitude better than those obtained with a glassy carbon (GC) electrode. The morphology of the deposited Pb was studied by using Kelvin force microscopy. The deposition was more uniform on the nanocarbon film than that on the GC. These results indicate that the uniform surface of the nanocarbon film realized the homogeneous deposition of metal ions and reduced the noise level due to the small surface area.
In this work, electrocatalytic hydrogenation (ECH) of phenol to cyclohexane and cyclohexanol was studied. Experiments were run in a H-type cell with a Pt sheet as anode. The cathode material and structure were found to have a large effect on the ECH of phenol. Among the cathodes studied, the 1.5% Pt supported on graphite gave the highest product yield and current efficiency. Temperature was another important variable, the yield of cyclohexane increased from 44.1% at 20°C to 63.7% at 60°C, but then dropped back to 50.3% at 80°C. Effects of electrolyte composition on ECH of phenol were also investigated. The yield of cyclohexane was highest when 0.2 mol/L HClO4 as electrolyte. Variable current studies in the range of 10–90 mA showed an increase in product yields with increasing current from 10–30 mA, but yields decreased when current above 70 mA. The suitable starting concentration of phenol was 50 mmol/L.
A new type of oscillation, which we name regeneration oscillation, is investigated in detail. The regeneration oscillation is the ordinary potential oscillation with the higher turning potential lower than 0.85 V appearing repeatedly after the potential stays at a value higher than 1.0 V for a long time, of the order of 10 min or an hour. The oscillation has been observed during the oxidation of methanol, formaldehyde, and formic acid at 315 K when their concentrations are high, 1 or 10 mol/L (M), in the presence of high chloride ion concentrations, such as 10−2 M, at a current far lower than the maximum current for the appearance of ordinary oscillation. The reason for the appearance of regeneration oscillation has been found by voltammetry and surface-enhanced infrared absorption spectroscopy to be due to the presence of two potentials for oxidizing adsorbed CO, one shifting to a value higher than 1.0 V and the other remaining unchanged, with increasing chloride ion concentration.
We studied the efficiency and accuracy of a general purpose finite element software in the numerical solution of electrochemical models. Typical numerical complications like boundary singularities, stiffness and multiscale problems were addressed. The convergence order was determined for various mesh refinement strategies. As a general rule, the numerical efficiency of the software proved adequate to the problems dealt, but the default generated meshes and the adaptive mesh adjustment do not work properly, if high levels of accuracy are required. Therefore, a manual adjustment of the mesh control parameters is indispensable. A thorough discussion of the problem of adjusting the mesh was presented to serve as a general introduction to the subject for beginners in the field. Additionally, it was suggested a general approach for mesh optimization through which the convergence rate can be considerably increased.
The performance of a batch electrocoagulation cell (rotating cylinder electrochemical reactor) in the demulsification of crude oil emulsions was investigated. The cell used a rotating Al cylinder as anode and a stationary cylindrical screen of aluminum as cathode. Parameters studied are the current density, the NaCl concentration, initial pH, the anode rotation speed, initial oil concentration and the nature of the supporting electrolyte. Increasing the current density led to increasing the rate of de-emulsification; a current density of 11.4 mA/cm2 allowed complete separation in 10 minutes while a current density of 17.1 mA/cm2 allowed complete separation in 6 minutes. The optimum pH range for the electrocoagulation is 7–11, acidic media (pH 3–5) retarded the electrocoagulation. The increase in the concentration of the NaCl led to an increase in the rate of oil removal. Higher electrolyte conductivity of the emulsion increased the rate of oil removal. Anode rotation was found to have a strong effect in improving oil removal efficiency. The higher the initial concentration of the emulsion, the higher the rate of oil removal. NaOH was found to be the best electrolyte, followed by NaCl, then KCl and finally NH4Cl.
In the study, ternary oxides coated Ti/SnO2-Sb2O5-IrO2 anode was used for degradation of 16 priority polycyclic aromatic hydrocarbons (PAHs) in a laboratory scale electrochemical batch reactor. To determine the optimum conditions for electrochemical degradation of PAHs from produced water, Box-Behnken design was used with three independent variables, viz., current density, pH and electrolysis time and response variable, viz., ΣPAHs removal %. Quadratic regression model was recommended as the best fit model. The results of Analysis of Variances (ANOVA) exhibited that the regression model adequately described the functional relationship between the independent variables and the response. This study affirmed that electrochemical degradation of PAHs followed first-order kinetics.
To well understand the mechanism of acid stratification in vented lead-acid batteries, the distributions of sulfuric acid in the vertical direction were measured by a refractive index meter. Also, the measurement of the electrochemical potential distributions in the vertical direction was tried using four dynamic hydrogen electrodes (DHEs). The acid stratification and its relaxation were confirmed by the measurement of sulfuric acid distributions during the charge/discharge and the rest state. There was a difference of four times in the time constant of the acid stratification relaxation between the upper part (top) and the lower part (bottom). This suggests that the acid diffusion is not a dominant reaction of the acid stratification relaxation. The local charge and discharge simultaneously must be occurred on the positive and negative electrode individually due to the electrochemical potential difference. In other words, the electrochemical potential difference probably is the dominant driving force of the acid stratification relaxation. The electrochemical potential distributions in the vertical direction were actually measured using the four DHEs.
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