Solid Oxide Electrolyte Galvanic Cell Research Articles

Determination of standard thermodynamic properties of Sb2O3 by a solid-oxide electrolyte EMF technique

A solid oxide electrolyte galvanic cell has been employed to obtain the thermodynamic properties of antimony trioxide Sb2O3 in the temperature range from 782 to 1080K. Standard Gibbs energy of formation ΔfG°, the standard enthalpy of formation ΔfH°298 and standard entropy S°298 were obtained by the electromotive force (EMF) method. The experimental procedure has been improved in order to increase the accuracy of the existing thermodynamic data. The obtained results have been compared to the data gathered in the previous studies. The standard Gibbs energies of formation obtained from multiple galvanic cells are linear functions of temperature as:ΔfG°/kJmol−1=−679.82+0.235T/K±0.413 (782−903.65K) both phases are solidΔfG°/kJmol−1=−739.53+0.301T/K±0.502 (903.65−929.15K) Sb—liquid; Sb2O3—solidΔfG°/kJmol−1=−682.21+0.239T/K±0.419 (929.15−1080K) both phases are liquidThe standard enthalpy of formation ΔfH°298 (−709.74/kJmol−1) and standard entropy S°298 (124.05/J(molK)−1) were calculated for Sb2O3 using the measured values and cp functions given by previous studies.

Molten Alkali Carbonate as an Effective Oxygen Electrode for a Solid Oxide Electrolyte Galvanic Cell

The excellent performance, recently reported in the literature, of a solid-state oxygen concentration cell equipped with an alkali carbonate-based electrode has been interpreted in accordance with the proposition that the carbonate is an alkali-ion conductor. This interpretation is the consequence of all facts known about the electrochemical behavior of solid and liquid alkali carbonates. The new view allows to refrain from postulating fast-diffusing peroxycarbonate ions as prerequisite for the function of the electrode and, thus, is much more realistic considering the bulkiness and voluminousness of the peroxycarbonate ion in comparison with an alkali ion.

Standard Gibbs energy of formation of tellurium dioxide measurement by a solid-oxide electrolyte EMF technique

The standard Gibbs energy of formation of TeO2 in the temperature range 369–795°C was measured by the EMF method involving solid-oxide electrolyte galvanic cells of the type:(−)Pt,Ir,Te(s,l),TeO2(s,l)|YSZ|O2,Pt(+),where YSZ denotes stabilized zirconia with 8.5mass percent of yttrium oxide. The standard Gibbs energies of formation obtained from the above cells are linear functions of temperature as:ΔfG° (kJ/mol)=−317.09+0.180T(K)±0.307(642–722.15K) both phasess are solid.ΔfG° (kJ/mol)=−318.01+0.181T(K)±0.308(722.15–1005.8K) Te – liquid; TeO2 – solid.ΔfG° (kJ/mol)=−256.26+0.120T(K)±0.226(1005.8–1068K) both phases are liquid.

Thermodynamic Characterization of the Eutectic Phase Mixture NaNbO3/Na3NbO4. II: Solid‐State Electrochemical Investigation

The difference in the standard Gibbs‐free energies of NaNbO3 and Na3NbO4 has been determined by means of two electrochemical approaches based on potentiometric solid oxide electrolyte galvanic cells. The results are consistent with each other and prove the phase equilibrium between the niobates to be univariant. Quantitatively, the data can be represented by (525°–700°C) image The results are in between a wide range spanned by estimated literature data and are close to the findings of a previous manometric study.

Thermodynamic characterisation of some doped lanthanum chromites used as interconnects in SOFC

The solid-oxide electrolyte galvanic cell method has been employed in order to characterize, from the thermodynamic point of view, some materials based on substituted lanthanum chromites: La 1− x M x CrO 3 (where M=Sr, Ca; x=0.2, 0.3) and La 0.8Sr 0.2Cr 0.95Mg 0.05O 3. The thermodynamic properties represented by the relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the partial pressures of oxygen, have been obtained as a function of temperature and substituent nature within the temperature range of 1073–1273 K and in reducing atmosphere (10 −5 Pa). The influence of oxygen stoichiometry change on thermodynamic properties was examined using the data obtained by a coulometric titration technique coupled with EMF measurements. An attempt to verify a previously proposed defect-structure model is also made.

Zinc(II) oxide-zinc(II) molybdate composite humidity sensor

Humidity sensing properties of composites made from ZnMoO 4 (ZM) and ZnO (ZO) were investigated. Sintered polycrystalline disks of ZnMoO 4 (ZMZO-10) and ZnO (ZMZO-01) and composites of ZM and ZO in the mole ratios 8:2, 6:4, 4:6 and 2:8 designated as ZMZO-82, 64, 46 and 28, respectively, were subjected to dc resistance measurements as a function of relative humidity in the range of 5–98% RH. The dc conductance measurements were carried out on the samples from which the activation energies were determined. Thermoelectric power measurements in the temperature range 250–400 °C revealed the materials to be n-type. The stability of the composites was evaluated by emf measurements by constructing solid oxide electrolyte galvanic cells with a view to (a) correlate the metastable coexistence of ZnO with ZnMoO 4 without forming ZnO+Zn 3MoO 6 and (b) to detect moisture in hydrogen streams. The metastable coexistence of ZnO with ZnMoO 4 in the composites was confirmed by SEM studies. The dc resistance of these hybrid oxides decreased on exposure to humidity at room temperature and the use of a mixture of oxides was found to be effective for optimizing humidity sensing performance in dc mode. The composite ZMZO-28 has the highest humidity sensitivity, greater than 2×10 3, with a response time of approximately 3 min, attributed mainly to the optimization of pore size and its even distribution in a biphasic matrix which is a metastable mixture of the two terminal phases, viz. ZnMoO 4 and ZnO.

Thermodynamic properties of the SrFeO 2.5 and SrMnO 2.5 brownmillerite-like compounds by means of EMF-measurements

The solid-oxide electrolyte galvanic cell method has been employed in order to obtain thermodynamic properties of the brownmillerite-like compounds SrFeO 2.5 and SrMnO 2.5 within the temperature range of 1073–1273 K. The standard Gibbs energy, the enthalpy and the entropy of formation, as well as the partial pressures of oxygen have been obtained. The experimental thermodynamic data have been compared to the existing theoretical estimated values.

Thermodynamic properties of some perovskite type oxides used as SOFC cathode materials

The solid-oxide electrolyte galvanic cells method has been employed in order to obtain the thermodynamic properties of some perovskite-type materials based on lanthanum strontium manganite and lanthanum strontium ferrite manganite. The relative partial molar free energies, enthalpies and entropies of oxygen dissolution in the perovskite phase, as well as the partial pressures of oxygen have been obtained in the temperature range of 1073–1273 K. By solid state coulometric titration, the initial composition of the perovskite phase was altered under controlled conditions. The results evidence the influence of the oxygen relative stoichiometry change on the thermodynamic properties. The effect of the iron content and of the overall A-site stoichiometry is also discussed. Broadening the potentialities of solid state EMF techniques, the method was proved very useful in thermodynamic studies when searching improved cathode materials used in solid oxide fuel cells (SOFC).

Thermodynamic studies on Cs 4U 5O 17(s) and Cs 2U 2O 7(s) by emf and calorimetric measurements

The oxygen potentials over the phase field: Cs 4U 5O 17(s)+Cs 2U 2O 7(s)+Cs 2U 4O 12(s) was determined by measuring the emf values between 1048 and 1206 K using a solid oxide electrolyte galvanic cell. The oxygen potential existing over the phase field for a given temperature can be represented by: Δ μ(O 2) (kJ/mol) (±0.5)=−272.0+0.207 T (K). The differential thermal analysis showed that Cs 4U 5O 17(s) is stable in air up to 1273 K. The molar Gibbs energy formation of Cs 4U 5O 17(s) was calculated from the above oxygen potentials and can be given by, Δ f G 0 (kJ/mol)±6=−7729+1.681 T (K). The enthalpy measurements on Cs 4U 5O 17(s) and Cs 2U 2O 7(s) were carried out from 368.3 to 905 K and 430 to 852 K respectively, using a high temperature Calvet calorimeter. The enthalpy increments, ( H 0 T − H 0 298), in J/mol for Cs 4U 5O 17(s) and Cs 2U 2O 7(s) can be represented by, H 0 T − H 0 298.15 (Cs 4U 5O 17) kJ/mol±0.9=−188.221+0.518 T (K)+0.433×10 −3 T 2 (K)−2.052×10 −5 T 3 (K) (368 to 905 K) and H 0 T − H 0 298.15 (Cs 2U 2O 7) kJ/mol±0.5=−164.210+0.390 T (K)+0.104×10 −4 T 2 (K)+0.140×10 5(1/ T (K)) (411 to 860 K). The thermal properties of Cs 4U 5O 17(s) and Cs 2U 2O 7(s) were derived from the experimental values. The enthalpy of formation of (Cs 4U 5O 17, s) at 298.15 K was calculated by the second law method and is: Δ f H 0 298.15=−7645.0±4.2 kJ/mol.

Molar Gibbs energy formation of RbUO3(s)

The molar Gibbs energy of formation of RbUO3(s) was determined by measuring the oxygen pressure over the phase field, RbUO3(s) + Rb2U2O7(s) + Rb2UO4(s), using a solid oxide electrolyte galvanic cell in the temperature range 920 to 1100 K and the partial pressure of rubidium using the Knudsen effusion mass loss method in the temperature range 1305 to 1459 K. The oxygen potential and the rubidium potential existing over the phase field can be respectively given by Δμ(O2)±0.4(kJ mol−1) = −531.6+0.2026T(K) and Δμ(Rb)±0.6(kJ mol−1) = −152.7+0.018T(K).

ChemInform Abstract: Molar Gibb′s Free Energy of Formation of Rb2U4O11(s) by Solid Oxide Electrolyte Galvanic Cell.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Molar Gibbs' free energy of formation of Rb 2U 4O 11(s) by solid oxide electrolyte galvanic cell

The molar Gibbs' free energy of formation of Rb 2U 4O 11 was determined by measuring the oxygen potentials over the Rb 2U 4O 11 + Rb 2U 4O 12 system using a solid oxide electrolyte galvanic cell with Ni + NiO as reference electrode in the temperature range 985–1186 K. It was found by X-ray diffraction analysis that Rb 2U 4O 11 coexists with Rb 2U 4O 12 up to 1300 K. The molar Gibbs' free energy formation of Rb 2U 4O 11 is calculated from the e.m.f. values and can be given by: Δ f G° (kJ mol −1) ± 0.65 = −5348.87 + 1.076 T (K). The kinetics of oxidation of Rb 2U 4O 11 in air, studied by thermogravimetry indicated that the reaction is phase boundary controlled with an activation energy of 123.6 kJ mol −1.

Electrocatalytic Reactivity of Hydrocarbons on a Zirconia Electrolyte Surface

An experimental survey of the electrochemical reactivity of five common fuel species was made employing a solid oxide electrolyte galvanic cell with porous Au and Pt electrodes in the temperature range 700°–850°C. The electrolyte used was (SSZ). The fuel species electro‐oxidized at the anode were: , , , , and . Rates of reaction were determined coulometrically, so that species other than could have undergone an undetermined amount of thermal dissociation during electro‐oxidation. The concomitant reactivity of , which is reduced at the cathode, was also investigated. The current‐overpotential behavior at both the cathode and anode was found to be similar whether Au or Pt was used to form the porous electrodes. In the low overpotential range, the rate of charge transfer is found to be rate determining for both the cathodic and anodic reactions. Activation enthalpies obtained from an analysis of the data in this low overpotential range are also found to be similarly independent of the electrode materials. Reduction of the electrolyte by current blackening leads to two to three orders of magnitude increase in both the cathodic and anodic current density at a given overpotential. Again, the current overpotential characteristics obtained with Au and Pt electrodes are very similar. Activation enthalpies obtained with the electrolyte in the blackened state do not deviate significantly from those obtained with an unblackened electrolyte. These experimental observations are consistent with a reaction mechanism in which the major electrochemical steps occur at active sites on the electrolyte surface rather than on the metal electrodes. The electrochemical reaction sites are hypothesized to be oxygen vacancies with electrons migrating along the electrolyte surface to or away from these active sites. Thus, an effective localized electronic conductivity of the electrolyte surface is postulated.

Thermodynamic stability of Sb 2O 3 by a solid-oxide electrolyte e.m.f. technique

The potentials of the solid-oxide electrolyte galvanic cells: Pt|C|Sb(cr)|Sb 2O 3(cr)|ysz|air { p( O 2 p ° )=0.21}|Pt , from 662 to 890 K, and Pt|C|Sb(l)|Sb 2O 3(l)|ysz|air { p( O 2 p ° )=0.21}|Pt , from 948 to 1051 K, where ysz denotes 15 mass per cent of Y 2O 3 stabilizing ZrO 2 have been measured over the temperature ranges shown. These have been used to derive the standard molar Gibbs energies of formation: Δ f G m °( Sb 2O 3,cr ,T)/(kJ·mol −1)=(−686.36+0.24594T/ K)±0.80 , Δ f G m °( Sb 2O 3,l ,T)/(kJ·mol −1)=(−663.42+0.21953T/ K)±0.65 . Even with the high precision of the e.m.f. technique, the orthorhombic-to-cubic transformation of Sb 2O 3 at 846 K could not be detected. Hence it has been assumed that Sb 2O 3 saturated with Sb remained in the orthorhombic form at least up to 895 K. A third-law treatment of the Δ f G m o(Sb 2O 3, cr, T) results has shown the absence of significant temperature-dependent errors in e.m.f. and has yielded a value of −(706.0 ± 2.0) kJ · mol −1 for Δ f H m o(Sb 2O 3, cr, orthorhombic, 298.15 K). The e.m.f.s in the range 895 to 950 K have been found to be irreproducible, the reasons for which have been discussed in the light of mutual solubility and proximity of the transition temperature of Sb and Sb 2O 3. The standard molar Gibbs energy expressions for solid and liquid Sb 2O 3 have yielded a value of 22.9 kJ · mol −1 for the difference in the two intercepts, in good agreement with 21.8 kJ · mol −1 calculated from the standard molar enthalpy of transformation of Sb 2O 3 from orthorhombic to cubic and of fusion of Sb and Sb 2O 3 reported in the literature (neglecting ∫ C p, m ° d T terms). A comparison of the Δ f G m o( T) results with those from earlier e.m.f. studies has also been made.

The role of sintering time on reversibility of Ni(s)?NiO(s) electrodes for high temperature solid oxide electrolyte galvanic cells

The reversibility of solid electrolyte galvanic cells such as $${\text{Mo/Ni(s)}}--{\text{NiO(s)/CSZ/Fe(s)}}--{\text{Fe}}_{{\text{1}}--\delta } {\text{O(s)/Mo}}$$ has been studied with respect to the sintering time of the active powders. Pellets from short (7h) and long (14h) sintering times have been prepared and assembled to give the above cells. Each of them has been thermally cycled and only the cells containing Ni(s)-NiO(s) electrodes prepared with a long sintering time give emf versus T curves which are independent of cycle. These values are in close agreement with the literature. For the cell reaction $${\text{NiO(s)}} + (1 - \delta ){\text{Fe(s) = Ni(s)}} + {\text{Fe}}_{1 - \delta } {\text{O(s)}}$$ the free energy change $$\Delta G = - (27.85 \pm 0.06) - (0.02157 \pm 0.00004)T{\text{ kJ mol}}^{ - {\text{1}}} $$ has been found in the temperature range 977–1350 K.

Thermodynamic properties of Fe 2Mo, Fe 3Mo 2, and FeMoO 3: galvanic-cell measurements using solid-oxide electrolyte

The e.m.f.'s of the following solid-oxide electrolyte galvanic cells have been measured over the temperature ranges shown. FeMoO 3, Fe 3Mo 2, Fe 0.933MO 0.067|O 2−|Fe 0.947O, Fe, (1240 to 1320 K), (1) FeMoO 3, Fe 2Mo, Fe 0.95MO 0.05|O 2−|Fe 0.947O, Fe, (1168 to 1232 K), (2) FeMoO 3, Fe 3Mo 2, Fe 2MO |O 2−|Fe 0.947O, Fe, (1160 to 1222 K), (3) FeMoO 3, Fe 3Mo 2, MO |O 2−|Fe 0.947O, Fe, (1276 to 1366 K), (4) The results have been used to obtain the standard Gibbs energies, enthalpies, and entropies of formation of Fe 2Mo, Fe 3Mo 2, and molybdate FeMoO 3 in the temperature ranges of investigation. The thermodynamic quantities for Fe 2Mo and Fe 3Mo 2 are compared with those of isostructural phases in the Fe + W, Co + Mo, and Co + W systems.

Electrochemical determination of the standard Gibbs free energy change of the graphite-Oxygen reactions

A calcia doped zirconia solid oxide electrolyte galvanic cell was investigated in the temperature range of 700–950°C to directly and more accurately measure the standard Gibbs free energy change of the following reactions: CO(g) + 1 2 O 2(g) = CO 2(g) C ( graphite) + CO 2( g) = 2 CO( g). The results obtained in the present investigation are well within the scatter band of the calorimetric and spectroscopic data.

The Determination of the Amount of Oxygen in Molten Copper-Nickel and Copper-Silver Alloys by the EMF Method

Abstract Using the following solid oxide-electrolyte galvanic cells, Pt/air//ZrO2 (+CaO) O//(in Cu–Ni alloy)/Mo and Pt/air//ZrO2 (+CaO) O//(in Cu–Ag alloy)/Mo, the electromotive forces of the cells have been measured as a function of the oxygen concentration in copper-nickel or -silver alloys at oxygen concentrations ranging from several ppm to 1000 ppm, at 1210°C for copper-nickel alloys and at 1100°C or 1200°C for copper-silver alloys respectively. The activity coefficient of oxygen has been determined from the electromotive force for the alloy systems investigated. In the case of copper-nickel, the activity coefficient of oxygen decreases with an increase in the nickel concentration and also with a decrease in the oxygen concentration. The solubility of oxygen in the copper-nickel alloy has also been measured at 1210°C by the use of the following galvanic cell, Pt/air//ZrO2(+CaO)//O(in Cu–Ni alloy), NiO/Mo.