Open-circuit Emf Research Articles

UAS based Li-ion battery model parameters estimation

Estimation of Lithium-ion (Li-ion) battery model parameters is key for accurately determining battery state of charge (SOC). Estimating these parameters requires substantial experimental effort. This work reduces the experimentation required, by using universal adaptive stabilization (UAS) for estimating parameters appearing in battery model state equations. Accuracy of estimated model parameters is verified by comparing the estimated and measured battery terminal voltage. SOC obtained using the estimated model parameters, and open circuit EMF vs SOC curve, captures effects due to discharge currents of small magnitude, which Coulomb counting, well known filtering methods ignore. Rigorous mathematical analysis supports the experimental results presented.

Electron-Ion Transport in ZrO2-Y2O3-CeO2Ceramics

Simultaneous conduction of oxide ions and electrons in solid ceramic systems provides the capability for oxygen transport under a concentration gradient without the need for an externally applied electric field. In the present study, ionic transference numbers have been measured in the ZrO2-5.8%Y2O3-10%CeO2 system by open circuit Emf measurements involving different metal/metal oxide electrodes. In order to correlate the ionic transference number with grain size, high-density ceramic discs of different grain sizes (50 nm–5 μm) were prepared by sintering pressed powders at various temperatures and times. Hydrothermal synthesis was used to prepare nanocrystalline powders of the above material with uniform crystallite size (10 nm) and chemistry. Emf measurements on the samples suggested both ionic and electronic transport, the ionic transference number decreasing with increase in the grain size. This observation was attributed to an increase in the amount of continuous crystalline grain boundary phase in the ceramics as the grain size increased. The presence of crystalline silicate and zirconate phases in the grain boundary region was confirmed by electron microscopic imaging combined with microanalysis. In the large grain (5 μm) ceramics, the ionic transference number decreased linearly with temperature. As the grain size decreased, a maximum occurred in the ionic transference number vs. temperature curve. This maximum became more pronounced at smaller grain sizes. Better grain-grain contact and the doping effect of trivalent Ce in the grain boundary core are proposed to explain this observation.

Investigation of defect equilibria in YBa 2Cu 3O x by a solid state electrochemical method

The partial pressure of oxygen, P(O 2), in equilibrium with YBa 2Cu 3O x was determined as a function of oxygen composition, x, and temperature, T, in the range 6.35> x>5.97 and 1120> T>825 K. A solid state electrochemical method was used allowing for accurate control of composition by Coulometric titration and determination of P(O 2) by open circuit EMF measurements. Decomposition of YBa 2Cu 3O x was found to occur at x values as high as 6.1. Evidence for additional possible phase transitions for x>6.1 are discussed. Three relevant defect models are considered in detail and fitted to these and other data. The outcome of this analysis is a model that is consistent with all the available data and assumes that the dominant defects are neutral oxygen interstitials, O t ∗ and that the concentration of charged defects is small compared to [ O i ∗ ]. The hole concentration, p, follows a P( O 2) 1 2 dependence over a significant range of x. The relative change in the position of the Fermi energy upon reduction from x=6.35 to x=6.1 is 0.2 eV. The partial molar enthalpy of oxygen in YBa 2Cu 3O 6.1 with respect to pure oxygen is 179 kJ/mol. It is suggested that the chemical and tracer diffusion coefficient are independent of the diffusivity determined from conductivity. Information concerning the thermodynamic factor and the enthalpy of oxidation is presented.

Potentiometric determination of activities in the two-phase fields of the system Na 2O(α)Al 2O 3

Three compounds have been found to be stable in the pseudobinary system Na 2O(α)Al 2O 3 between 825 and 1400 K; two nonstoichiometric phases, β-alumina and β″-alumina, and NaAlO 2. The homogeneity of β-alumina ranges from 9.5 to 11 mol% Na 2O, while that of β″-alumina from 13.3 to 15.9 mol% Na 2O at 1173 K. The activity of Na 2O in the two-phase fields has been determined by a solid-state potentiometric technique. Since both β- and β″-alumina are fast sodium ion conductors, biphasic solid electrolyte tubes were used in these electrochemical measurements. The open circuit emf of the following cells were measured from 790 to 980 K: ▪ ▪ ▪ The partial molar Gibbs' energy of Na 2O relative to γ-Na 2O in the two-phase regions can be represented as: Δ Ḡ Na 2O (α- + β-alumina) = −270,900 + 24.03 T, Δ Ḡ Na 2O (β- + β″-alumina) = −232,700 + 56.19 T, and Δ Ḡ Na 2O (β″-alumina + NaAlO 2) = −13,100−4.51 T J mol −1. Similar galvanic cells using a Au Na alloy and a mixture of Co + CoAl 2+2 x O 4+3 x +(α)Al 2O 3 as electrodes were used at 1400 K. Thermodynamic data obtained in these studies are used to evaluate phase relations and partial pressure of sodium in the Na 2O(α)Al 2O 3 system as a function of oxygen partial pressure, composition and temperature.

Standard Free Energy of Formation of Iron Iodide

not Available.

Electrochemical cell investigations of LixTiS2 and LixNayTiS2 using a polymer electrolyte

Ionic complexes of polymers are a new class of ionic solids which deserve special attention(1). The open-circuit EMF of cell (A) has been measured as a function of composition, x, in LixTiS2 at temperatures between 30 and 100 C. Li/LiC2O2F3 in polyethylene oxide/LixTiS2 (A) The results agree with a previous study(2) in which a liquid organic-solvent electrolyte was used. Thus, the LiC2O2F3-polyethylene oxide complex is a suitable lithium electrolyte for open circuit measurements in this temperature range.Open-circuit EMF's of cell (B) have also been measured for values of x between 0.2 and 0.8. Li/LiC2O2F3 in polyethylene oxide/LixNa0.16TiS2 (B) Some LixNa0.16TiS2 compounds with x between 1.0 and 1.8 have also been prepared, but EMF's of cells using these materials as cathodes were unstable. The measured compositional variation of the lithium chemical potential in LixNa0.16TiS2 is discussed in terms of a recent thermodynamic model(3) to increase the understanding of alkali-metal interactions in intercalated dichalcogenides. The results are also used to calculate a theoretical energy density and to assess the electrode applications of these novel materials.

Kinetics, limit cycles, and mechanism of the ethylene oxidation on platinum

The oxidation of ethylene on polycrystalline Pt films was studied in a CSTR at atmospheric pressure and temperatures between 200 and 400 °C. The new technique of solid electrolyte potentiometry (SEP) was used to monitor the activity of oxygen on the metal catalyst. To this end the platinum film catalyst also served as one of the electrodes of a solid-electrolyte oxygen concentration cell and the open-circuit emf of the cell was monitored during reaction. It was found that the steady-state surface oxygen activity a 0 satisfies the equation a 0 = K s P O 2 P ET , where K s depends on temperature only. The reaction rate is first order in ethylene and adsorbed oxygen. Over a certain range of temperature and gas-phase composition both the surface oxygen activity and the reaction rate exhibit self-sustained oscillations. Limit cycles appear only over a well-defined range of surface oxygen activity a 0 values. The oscillations can be explained in terms of the stability of a surface platinum oxide. The reaction mechanism is discussed in light of these observations.

The Measurement of Sulfur Chemical Potential Differences Using a Calcium Fluoride Solid Electrolyte

Calcium fluoride has been conventionally used as a solid electrolyte to measure fluorine chemical potentials in high temperature systems. However in this investigation, this electrolyte has been used as a sulfur sensor. Opencircuit emf measurements have been carried out with the following four galvanic cellsThe cells were investigated in the temperature range, 500°–900°C. Using Richardson and Antill's data for the standard Gibbs energy of formation of, the standard Gibbs energies of formation of , , , and have been determined.

Solid electrolyte aided study of the ethylene oxide oxidation on silver

The oxidation of ethylene oxide on polycrystalline Ag films supported on stabilized zirconia was studied in a CSTR at atmospheric pressure and temperatures between 250 and 400 °C. The new technique of solid electrolyte potentiometry (SEP) was used to monitor the chemical potential of oxygen adsorbed on the metal catalyst. To this end the silver film catalyst also served as one of the electrodes of a solid electrolyte oxygen concentration cell and the open-circuit emf of the cell was monitored during reaction. It was found that the steady-state surface oxygen activity α o is given by a 0 = P O 2 1 2 /(1 + K ETOXP ETOX 2), with K ETOX = 3.3 · 10 −5 exp ( 10,600 T ) . This equation as well as the kinetics can be explained in terms of a simple reaction mechanism.

Chemistry at catalytic surfaces: The SO 2 oxidation on noble metals

The high temperature solid electrolyte cell air, M¦ ZrO 2 (8% Y 2O 3 )¦M , air-SO 2SO 3, where M is Pt, Ag, or Au, was used to monitor the oxygen activity on Pt, Ag, or Au catalyst films exposed to mixtures of O 2, SO 2, and SO 3 at temperatures above 400 °C and 1 atm total pressure. One electrode functioned simultaneously as both electrode and catalyst. The opencircuit EMF of the cell reflected the oxygen activity on the working catalyst and simultaneously the steady-state chemical kinetics were observed. For Pt it was found that the surface oxygen activity generally does not equal the gas phase P O 2 , but is determined by P SO 2 or the P SO 3 P SO 2 ratio, depending on the temperature and gas phase composition. These observations suggest that the rate-limiting step in the SO 2 oxidation on Pt is not generally the reaction between chemisorbed oxygen and gaseous SO 2, except at high temperatures and very low P so 2 , but rather the desorption of a chemisorbed phase of SO 3 or the adsorption of oxygen, depending upon the temperature, P SO 2 , P SO 3 , and P O 2 . The results with Au and Ag films show that chemisorbed SO 3 is also formed on these metals exposed to SO 2, O 2 mixtures. The values of surface oxygen activity compared to those obtained for Pt, provide an explanation for the weakly catalytic and noncatalytic properties of Au and Ag, respectively, for the SO 2 oxidation.

ChemInform Abstract: ELECTROMOTIVE FORCE MEASUREMENTS ON CELLS INVOLVING BETA‐ALUMINA SOLID ELECTROLYTE

Open circuit emf measurements have been made to demonstrate that a two-phase, polycrystalline mixture of beta- alumina and alpha-alumina could be used as a solid electrolyte in galvanic cells with reversible electrodes fixing oxygen or aluminum chemical potentials. These measurements indicate that such a two phase solid electrolyte can be used to monitor oxygen chemical potentials as low as that corresponding to Al, Al2O3 coexistence. The activity of Na2O in beta-alumina in coexistence with alpha-alumina was also determined by emf measurements.

Transition from Ionic to Electronic Conduction in Pure ThO2 Under Reducing Conditions

Open‐circuit emf and ac conductivity studies were conducted on two batches of dense polycrystalline ThO2. The open‐circuit emf data were used to delineate the low‐po2 ionic domain boundary for “pure” ThO2, which is presented as a log Pθ line on a log Po2‐1/T diagram. In addition the ionic conductivity, σion, and the high‐Po2 log Pθ boundary were also determined, mainly from ac conductivity measurements, which also confirmed the Po2I/4 dependence of σp, the p‐type electronic conductivity, shown by other investigators. The main results are, for the first batch, log Pθ= 12.7−220.2 × 103/4.575T, log σion= 1.9−44.3×103/4.575T, and log Pθ=−1.0−31.4 × 103/4.575T; for the second batch, log Pθ=11.2−219.7 × 103/4.575T, log σion= 1.7−41.6 × 103/4.575T, and log Pθ=0.6−40.4 × 103/4.575T. The oxygen permeability of ThO2 tubes and the oxidation rate constant of Th were predicted from the conductivity and emf data and compared with direct measurements previously reported. The calculated and previously measured permeabilities agreed very well; however, the correlation between the predicted and previously measured oxidation kinetics was somewhat less satisfactory.

Batteries with Solid Ion‐Exchange Membrane Electrolytes: II . Low‐Temperature Hydrogen‐Oxygen Fuel Cells

Hydrogen‐oxygen fuel cells employing a commercial ion‐exchange membrane as the electrolyte are described. Some performance data on this type of cell operating at room temperature with a cation membrane in the hydrogen form and with hydrogen and oxygen at 1 atm are presented. The open circuit EMF is about 0.3 v below the value of 1.23 expected for a reversible cell. This deficiency is found to be caused by the oxygen electrode which does not achieve the reversible half‐cell potential. Equilibration of the membrane electrolyte with sulfuric acid prior to cell assembly results in improved polarization characteristics. Favorable features of these cells include their simple construction and their small unit thickness. In addition, the presence of as much as 67% in the hydrogen feed gas is found to have little effect upon performance. Since the electrolyte is a cross‐linked, water‐saturated polymer, the electrolyte is locked into the structure and cannot be leached from the cell when it is operated within the stability limits of the polymer. No dilution occurs from the water formed at the oxygen electrode during cell operation because it is rejected from the saturated electrolyte.