Exploring the mixed transport properties of sulfur(vi)-doped Ba₂In₂O₅ for intermediate-temperature electrochemical applications

Abstract

Thestabilised orthorhombic perovskite Ba2In1.8S0.2O5.3 was synthesised by solid state reaction at low-temperature. The mixed (electronic-protonic-oxide-ionic) conducting properties of this composition were investigated in detail for potential interest in a wide range of membrane applications including Protonic Ceramic Fuel Cells. The electrochemical analyses performed include impedance spectroscopy in wet/dry conditions of N2 and O2 and modified electromotive force measurements in wet/dry mixtures of N2/O2. In dry oxidising conditions the sample possesses mixed electronic-oxide-ionic contributions to the electrical transport in the whole range of temperature, associated with the equilibrium between oxygen vacancies and holes. In wet atmospheres, protonic species arise from the hydration reaction. Protons represent the dominant charge carriers for temperatures lower than 550 °C, while oxide-ions and holes are the major mobile species for temperatures higher than 700 °C. Appreciable mixed contributions to the electrical transport from protons, oxide ions and holes are confirmed between 550-700 °C. The experimental data obtained from modified electromotive force measurements and impedance spectroscopy fit well with the expected results according to the proposed defect chemistry model.

Temperature dependence of partial conductivities of the BaZr 0.7 Ce 0.2 Y 0.1 O 3-δ proton conductor

“…As mentioned, this technique is based on the defect chemistry of the system under the corresponding working conditions. In order to check the accuracy of the results, assessment of the transport numbers by a direct procedure developed previously based on a modified emf method was employed at 750 ºC [12,22]. The sample was located in parallel with a variable auxiliary resistor and submitted to a gradient of pO2 at a fixed condition of pH2O for determination of the electronic transport number and the total ionic transport number.…”

“…The sample was located in parallel with a variable auxiliary resistor and submitted to a gradient of pO2 at a fixed condition of pH2O for determination of the electronic transport number and the total ionic transport number. The observed electromotive force (Eobs) varies with the magnitude of the auxiliary resistance (Raux) as a consequence of the modification of the electronic current leakage, as follows [12,22]:…”

“…where C is a constant dependent of the protonic, oxide-ionic and electrode-polarisation resistances, Re is the electronic resistance and The protonic transport number was subsequently determined under a pH2O gradient, with an average value corresponding to the fixed pH2O of the first experiment, at a fixed condition of pO2 (corresponding to the average pO2 gradient of the first approach). The effect of the variable resistance on the electromotive force of the system may be represented as follows [12,22]:…”

Photocatalytic CO2 reduction by Cr-substituted Ba2(In2-Cr )O5·(H2O) (0.04 ≤ x ≤ 0.60)

“…Ba 2 In 2 O 5 has drawn increasing research interest regarding fast oxide ion and proton conduction due to its unique crystal structure [1][2][3][4][5][6]. Partial cationic and/or anionic substitution in Ba 2 In 2 O 5 brings marked changes in crystal structure, defect structure, and electronic structure resulting in a number of materials properties, which are interesting for various technical applications [2,[7][8][9][10][11][12][13][14][15][16][17][18][19]. For example, gallium or zirconium substituted Ba 2 In 2 O 5 for solid oxide fuel cells (SOFC) with an intermediate operating temperature range of 823 -1023 K was a research focus in recent years [13,[20][21][22].…”

Investigation into the Effect of Sulfate and Borate Incorporation on the Structure and Properties of SrFeO3-δ

“…As an extension to this work on cuprate superconductors, we have demonstrated successful oxyanion doping of perovskite materials for SOFC applications. This has included oxyanion (sulfate, silicate, phosphate) doping of Ba 2 (In/Sc) 2 O 5 electrolyte materials [13][14][15][16]. Doping with these oxyanions introduces disorder on the oxygen sublattice, leading to improvements in the ionic conductivity.…”