Ceria-based materials for high-temperature electrochemistry applications

This paper describes the experimental studies of multi-component solid state electrolytes based on CeO2 and their application in intermediate temperature electrochemical devices. Two important aspects are emphasized: the effect of different dopants’ ionic radius and concentration on the electrical properties of CeO2-based solid solutions in air and the influence of combined dopants on the electrolytic properties of solid electrolytes from the standpoint of the critical oxygen partial pressure pO2 at which point the values of the electronic and ionic components of conductivity are equal. Examples of usage of the developed multi-component Ce0.8(Sm0.75Sr0.2Ba0.05)0.2O2-δ electrolyte synthesized by solid state, laser evaporation and combustion methods and composites on the base of Ce0.8(Sm0.8Sr0.2)0.2O2−d electrolyte as a component of electrochemical devices such as solid oxide fuel cell, gas sensors and as a component of the mixed ionic and electronic conducting (MIEC) membranes for hydrogen and syngas gas production are cited.The present work was financially supported by Russian Foundation for Basic Research and Government of Sverdlovsk region, grant no. 13-03-96098

Pyrochlore-type Y2Ti2O7-based titanates as buffer layer materials for fuel-assisted solid oxide electrolysis cells

No abstract available.publishe

On the chemical stability of the structure and physical characteristics of the high-temperature spintronic composite EuO:Fe under normal conditions

The possibility of forming a limited solid solution Eu 1-x Fe x O in the structure of a spintronic composite material EuO:Fe obtained by the high-temperature solid-phase reduction method of a mixture of higher metal oxides is discussed. Its prevailing role in the formation of outstanding physical properties of this composite as a high-temperature spin injector is described from experimental and theoretical data. © 2018 Russian Academy of Natural Science. All Rights Reserved

Perovskite-Like Pr(A)MnO3 (A = Ca, Sr) as Anode Materials for Solid Oxide Fuel-Assisted Electrolysis Cells

Long-term degradation remains the main issue for the viability of solid oxide electrolysis cell (SOEC) technology as a practical hydrogen production system. One of the main specific degradation mechanisms in SOECs relates to the delamination phenomena at or near the electrolyte/anode interface. The principle of so-called fuel-assisted electrolysis is to supply the carbon-containing species which can react with oxygen at the anode side thus bringing down the oxygen chemical potential at the electrolyte/anode interface and improving its stability. The present work is aimed at the characterization of PrMnO3-based perovskites for potential application as anodes in solid oxide fuel-assisted electrolysis cells. Pr0.60-xA0.40MnO3±δ (A = Sr, Ca; x = 0 and 0.05) were synthesized by glycine-nitrate combustion technique. The characterization included XRD, SEM/EDS, XPS, dilatometry and thermogravimetry, measurements of electrical properties and oxygen permeability, and determination of oxygen nonstoichiometry. XRD analysis confirmed the formation of solid solutions with orthorhombic perovskite structure. The oxides exhibit negligible variations of oxygen content under oxidizing conditions while reducing p(O2) below 10-4 atm results in oxygen losses from the lattice and reduction of Mn cations. XPS results suggest that praseodymium remains in a 3+ oxidation state in the bulk of ceramics but may adopt a mixed 3+/4+ oxidation state at the surface. The lowp(O2) stability boundary of the perovskite phase at 800°C corresponds to ~10-17-10-16 atm; the stability domain is wider for Ca-substituted compositions and narrows with the introduction of A-site vacancies. Dilatometric studies confirmed good thermomechanical compatibility with common solid electrolytes under oxidizing conditions; however, reduction at operation temperatures (800°C) leads to undesirable chemical expansion. The electrical conductivity of Pr0.60-xA0.40MnO3±δ ceramics is p-type electronic and decreases with reducing p(O2) but still exceeds 40-50 S/cm under anticipated oxygen electrode operation conditions. The electrochemical activity of Pr0.6-xA0.4MnO3±δ electrodes was evaluated in contact with yttria-stabilized zirconia solid electrolyte as a function of relevant parameters (fabrication conditions, with and without buffer layers, with modifications via infiltration of praseodymia and/or doped ceria). The best performance was obtained for the cells with Pr0.55A0.40MnO3±δ electrodes (gadolinia-doped ceria buffer layers, PrOy load of ~33 wt.%) that showed anodic overpotential of around 50 mV under 500 mA/cm2 at 800°C in air.publishe

The development of electrolytes for intermediate temperature solid oxide fuel cells

This report describes a number of experimental studies on the solid state electrolytes for intermediate temperature solid oxide fuel cells (IT-SOFCs): Ce1-xLnxO2-δ (Ln = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb), some multicomponent systems Ce1-xLnx/2Ln x/2O2-δ (x = 0 - 0.20; Ln = Sm, La, Gd and L'n = Dy, Nd, Y), some systems with simultaneous doping by rare earth and alkali earth elements Ce0.8(Sm1-xMx)0.2O2-δ (M = Ca, Sr; x = 0.0 - 1.0) and Ce0.8(Sm1-x-yBayMx)0.2O2-δ (M = Ca, Sr; x = 0, 0.15, 0.20; y = 0.05, 0.1). Two important aspects are emphasized: the effect of different dopants' ionic radius and concentration on the electrical properties of CeO2 based solid solutions and the influence of the method of preparation on the structural properties of ceria ceramics and the electrochemical performance of single SOFCs on their base. To describe the electrolytic properties of solid electrolytes the notation of the electrolytic domain boundary (EDB) - the critical oxygen partial pressure P*O2 at which the values of the electronic and ionic components of conductivity are equal, were calculated and presented. The interpretation of these data will lead to a better understanding of, subsequent improvements to and ultimately, the commercialization of IT-SOFCs in Russia. © 2014 WIT Press.International Journal of Safety and Security Engineering;International Journal of Sustainable Development and Planning;WIT Transactions on Ecology and the Environmen

Solution combustion synthesis of α-Al2O3 using urea

The processes involved in the solution combustion synthesis of α-Al2O3 using urea as an organic fuel were investigated. The data describing the influence of the relative urea content on the characteristic features of the combustion process, the crystalline structure and the morphology of the aluminium oxide are presented herein. Our data demonstrate that the combustion of stable aluminium nitrate and urea complexes leads to the formation of α-alumina at temperatures of approximately 600-800 °C. Our results, obtained using differential thermal analysis and IR spectroscopy methods, reveal that the low-temperature formation of α-alumina is associated with the thermal decomposition of an α-AlO(OH) intermediate, which was crystallised in the crystal structure of the diaspore. © 2012 Elsevier Ltd and Techna Group S.r.l

Impact of Thermochemical Treatments on Electrical Conductivity of Donor-Doped Strontium Titanate Sr(Ln)TiO₃ Ceramics

The remarkable stability, suitable thermomechanical characteristics, and acceptable electrical properties of donor-doped strontium titanates make them attractive materials for fuel electrodes, interconnects, and supports of solid oxide fuel and electrolysis cells (SOFC/SOEC). The present study addresses the impact of processing and thermochemical treatment conditions on the electrical conductivity of SrTiO3-derived ceramics with moderate acceptor-type substitution in a strontium sublattice. A-site-deficient Sr0.85La0.10TiO3−δ and cation-stoichiometric Sr0.85Pr0.15TiO3+δ ceramics with varying microstructures and levels of reduction have been prepared and characterized by XRD, SEM, TGA, and electrical conductivity measurements under reducing conditions. The analysis of the collected data suggested that the reduction process of dense donor-doped SrTiO3 ceramics is limited by sluggish oxygen diffusion in the crystal lattice even at temperatures as high as 1300 °C. A higher degree of reduction and higher electrical conductivity can be obtained for porous structures under similar thermochemical treatment conditions. Metallic-like conductivity in dense reduced Sr0.85La0.10TiO3−δ corresponds to the state quenched from the processing temperature and is proportional to the concentration of Ti3+ in the lattice. Due to poor oxygen diffusivity in the bulk, dense Sr0.85La0.10TiO3−δ ceramics remain redox inactive and maintain a high level of conductivity under reducing conditions at temperatures below 1000 °C. While the behavior and properties of dense reduced Sr0.85Pr0.15TiO3+δ ceramics with a large grain size (10–40 µm) were found to be similar, decreasing grain size down to 1–3 µm results in an increasing role of resistive grain boundaries which, regardless of the degree of reduction, determine the semiconducting behavior and lower total electrical conductivity of fine-grained Sr0.85Pr0.15TiO3+δ ceramics. Oxidized porous Sr0.85Pr0.15TiO3+δ ceramics exhibit faster kinetics of reduction compared to the Sr0.85La0.10TiO3−δ counterpart at temperatures below 1000 °C, whereas equilibration kinetics of porous Sr0.85La0.10TiO3−δ structures can be facilitated by reductive pre-treatments at elevated temperatures

Impact of praseodymia additions and firing conditions on structural and electrical transport properties of 5 mol.% yttria partially stabilized zirconia (5YSZ)

Ceramics samples with the nominal composition [(ZrO2)0.95(Y2O3)0.05]1-x[PrOy]x and praseodymia contents of x = 0.05–0.15 were prepared by the direct firing of compacted 5YSZ + PrOy mixtures at 1450–1550 C for 1–9 h and characterized for prospective applicability in reversible solid oxide cells. XRD and SEM/EDS analysis revealed that the dissolution of praseodymium oxide in 5YSZ occurs via the formation of pyrochlore-type Pr2Zr2O7 intermediate. Increasing PrOy additions results in a larger fraction of low-conducting pyrochlore phase and larger porosity, which limit the total electrical conductivity to 2.0–4.6 S/m at 900 C and 0.28–0.68 S/m at 700 C in air. A longer time and higher temperature of firing promotes the phase and microstructural homogenization of the ceramics but with comparatively low effect on density and conductivity. High-temperature processing leads to the prevailing 3+ oxidation state of praseodymium cations in fluorite and pyrochlore structures. The fraction of Pr4+ at 600–1000 C in air is less or equal 2% and is nearly independent of temperature. 5YSZ ceramics with praseodymia additions remain predominantly oxygen ionic conductors, with p-type electronic contribution increasing with Pr content but not exceeding 2% for x = 0.15 at 700–900 C. The average thermal expansion coefficients of prepared ceramics are in the range of 10.4–10.7 ppm/K.publishe