In order to investigate an effect of the preparation process on protonic conductivity of La1−xBa1+xGaO4−δ, we attempt to prepare the samples with x = 0.1, La0.9Ba1.1GaO4−δ, by a liquid synthesis method as well as a conventional solid-phase method. Their electrical conductivities are measured from 300 to 900°C in various water vapor partial pressures, PH2O. From the result, it is found that the protonic conductivity is higher in the sample synthesized by the liquid synthesis method compared with that by the solid-phase method. In addition, it is also indicated that the PH2O-dependence of the electrical conductivity around 600°C is more significant in the sample prepared by the liquid synthesis method. This result implies that this method enhances proton dissolution in La0.9Ba1.1GaO4−δ at least around the temperature range. To investigate a crystal structure change by the synthesis method, we perform powder neutron diffraction measurements. The Rietveld and maximum entropy method (MEM) analyses demonstrate that nuclear density of the proton is clearly observed between neighboring O3 sites, and suggest that the liquid synthesis method makes a site occupancy of proton higher.
Electrolytic removal of ammonia was investigated by using zeolite packed electrolysis reactor in batch mode. The results showed that 27.8 mg N/L ammonia could be removed to a concentration as low as 0.3 mg N/L within 1 h. Nitrite, nitrate and chloramines were determined to be 0.02 mg N/L, 3.9 mg N/L and 15.8 mg Cl/L, respectively, which accounted for a total nitrogen removal of 80% after 1.5 h of electrolysis. The main components and crystalline structure of the packed zeolite were found to be unchanged after long time of electrolysis. The specific surface area and pore volume of zeolite increased from 15.9 m2/g and 0.05 cm3/g to 42.6 m2/g and 0.08 cm3/g, respectively, which might be caused by the removal of impurities and formation of new channels and cavities during electrolysis. The adsorption capacities of zeolite for ammonia before and after electrolysis were close.
Bipolar plates in fuel cells and redox flow batteries are one of the most expensive components, which become a crucial factor for their commercialization. In this report, nickel and carbon are co-electrodeposited from Watts solution containing carbon black powder, and the Ni-C composites are characterized by SEM, EDS, XRD and surface profilometry. The intrinsic passivation behavior and the sheet resistance of Ni-C are on a par with pure Ni when carbon is introduced less than 26 at% in the composite, but the introduction of carbon to Ni suppresses the increase in sheet resistance after a storage corrosion test, which invites the expectation of high durability as bipolar plate materials. This kind of approach where carbon is introduced to metal-based bipolar plates by electrodeposition can improve the surface properties of pure metal bipolar plates with maintaining their price competitiveness over graphite-based composites and other high cost manufacturing techniques.
As part of studies for finding active materials in the redox-flow battery system using ionic liquids (ILs) as electrolyte, we have synthesized [Fe(L)x][Tf2N]2 (L = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), or 2,2′:6′,2′′-terpyridine (terpy); Tf2N = bis(trifluoromethylsulfonyl)imide, x = 3 for bpy and phen; 2 for terpy), and examined their electrochemical properties in [BMI][Tf2N] (BMI = 1-butyl-3-methylimidazolium). From 1H-NMR and UV-vis absorption spectra, it was confirmed that three Fe(II) species exist as [Fe(L)x]2+ in [BMI][Tf2N] solution. Cyclic voltammograms (CVs) and chronoamperograms (CAs) of the [Fe(L)x]2+ species in [BMI][Tf2N] solution were measured at 25°C. In the CVs, two peaks corresponding to the redox couples of Fe(II)/Fe(III) were observed around 1 V vs. Ag/AgCl, and their redox reactions were found to be quasi-reversible. The diffusion coefficients of [Fe(L)x]2+ were estimated to be (3−9) × 10−7 cm2 s−1 by chronoamperometry. The standard rate constants for the redox reactions were estimated to be (2−6) × 10−3 cm s−1 at 25°C. Furthermore, the present Fe(II)/Fe(III) redox systems were found to be cycled stably. From these results, the [Fe(L)x]2+ species are expected to be used as cathode active materials for the redox-flow batteries using [BMI][Tf2N] as the electrolyte.
We have found that the current range is divided into two parts for the appearance of potential oscillation during methanol oxidation on polycrystalline platinum at 315 K when the methanol concentration is between 10 and 0.03 mol dm−3 (M). The current range for oscillation disappearance, named ΔI (od), increases with a decrease in the methanol concentration. At currents below the ΔI (od), the oscillation waveform is always a large-amplitude and long-period (sometimes of the order of an hour) oscillation, named oscillation L. At currents immediately above the ΔI (od), a small-amplitude and short-period oscillation, named oscillation S, is observed for 0.03 to 0.1 M methanol and oscillation L is for 0.3 to 10 M methanol. For the latter methanol concentrations, oscillation S also becomes observed at higher currents. Such a ΔI (od) has not been found for potential oscillations during formic acid or formaldehyde oxidation and, thus, the existence of the ΔI (od) is distinctive to potential oscillations during methanol oxidation.
One-dimensional electrochemical cellular automaton (1D-ECA) has been run for the calculation of the chemical impedance, in which quasi-sine voltage signal of the dimensionless period 2N, where N ranges from 2 to 13, is superposed on the equilibrium potential. The voltage and the resulting current are Fourier-transformed, and their ratio at the fundamental frequency is plotted in the complex impedance plane, giving the charge-transfer resistance and the Warburg impedance. The dependence of these quantities on the parameters of 1D-ECA has been examined. Another type of modulation based on alternating pulses has also been successfully tested.
As a kind of environmentally friendly corrosion inhibitor, the extract from pomelo peel was evaluated for C38 carbon steel in 1 M HCl solution. The corrosion inhibiting performances of the extract from pomelo peel was confirmed using electrochemical method, weight loss measurement and scanning electron microscope (SEM) observation in the temperature range between 298 and 328 K. The inhibition efficiency was found to increase with the concentration of the extract from pomelo peel. Electrochemical impedance spectroscopy (EIS) measurement indicated that the corrosion process of the steel was inhibited by the adsorption of the extract from pomelo peel, following a Langmuir-type isotherm.
LiCoO2 particles were coated with 33Li4GeS4·67Li3PS4 (mol%) solid electrolyte (SE) thin films by pulsed laser deposition (PLD). The all-solid-state cells using positive electrodes, composed of only LiCoO2 particles coated with SE thin films, were fabricated and their electrochemical performances were investigated. The cell was charged and discharged with a higher capacity of 67 mAh g−1 than that using LiCoO2 particles without SE-coating. Moreover, the capacity of all-solid-state cell increased to 80 mAh g−1 after enhancing the ionic conductivity of SE thin films by heat treatment at 200°C. The use of highly lithium-ion conductive thin films was effective in the formation of sufficient lithium-ion conduction paths in positive electrodes for bulk-type all-solid-state batteries.
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