D. Medvedev

Recent activity in the development of proton-conducting oxides for high-temperature applications

High-temperature proton-conducting materials constitute a unique class of oxide materials, which are able to exhibit protonic conductivity under hydrogen-containing atmospheres. Besides being of great fundamental interest, such oxide systems possess practical significance because they can achieve high protonic conductivity levels. This opens the possibility of using proton-conducting materials as electrolytes for a wide range of intermediate- and high-temperature solid oxide electrochemical devices. Recent advances in the field of solid oxide proton-conducting materials that belong to the class of perovskite-based materials (such as doped BaCeO3, BaZrO3, BaCeO3–BaZrO3, SrCeO3, and LaScO3) and to other classes of materials (such as doped Ba2In2O5, CeO2, and LaNbO4) are presented and analyzed in this review. In order to highlight the most appropriate materials for applications in electrochemical devices, the analysis is devoted to the establishment of correlations between compositional and structural characteristics and their transport, thermal and stability properties.

A new Dy-doped BaCeO3–BaZrO3 proton-conducting material as a promising electrolyte for reversible solid oxide fuel cells

The present work describes the features of the synthesis and physicochemical and electrical properties of a new Dy-doped BaCeO3–BaZrO3 proton-conducting electrolyte as well as its application in a reversible solid oxide fuel cell. The electrolyte material with a composition of BaCe0.5Zr0.3Dy0.2O3−δ (BCZD) is successfully synthesized by a citrate–nitrate combustion synthesis method followed by sintering at 1450 °C for 5 h. The as-prepared ceramic materials are found to possess high ceramic quality (∼16% of total shrinkage, 98% of relative density, no open porosity), improved electrical properties (19 and 13 mS cm−1 at 600 °C in wet air and wet hydrogen atmospheres, respectively) and acceptable chemical and thermal compatibilities with functional electrodes (NiO–BCZD and La2NiO4+δ–BCZD). An electrochemical cell with a 30 μm thick electrolyte is fabricated by a tape calendaring method and then characterized in solid oxide fuel cell (SOFC) and solid oxide electrolysis cell (SOEC) operation modes. The electrochemical characteristics, such as open circuit voltage (OCV), current density, power density and amount of hydrogen produced by electrolysis, are obtained and then compared with literature data. On the basis of comparative analysis, it can be deduced that Dy-doped cerate–zirconates can be considered as promising alternatives to traditional Y-doped ones due to sufficient levels of output characteristics of reversible solid oxide fuel cells and good properties of these electrolytes (average ion transport numbers are more than ∼0.9) in the SOFC and SOEC operation modes at 550–750 °C.

Development of the Cathode Materials for Intermediate-Temperature SOFCs Based on Proton-Conducting Electrolytes

High-temperature proton-conducting oxide materials are of great fundamental interest due to the phenomenon of proton conductivity which appears with oxygen-ionic conductivity in a humidified atmosphere and is strongly dependent on temperature. The practical interest associated with the use of such Co-ionic electrolyte materials in solid oxide fuel cells (SOFCs) derives from the increased efficiency as a result of the higher open circuit voltage and, correspondingly, power output characteristics in comparison with those of SOFCs based on unipolar oxygen-ion conducting electrolytes. Today there is much work directed toward enhancing an SOFC’s electrochemical characteristics by developing new cathode materials that have excellent electrocatalytic activity. Thermal affinity between electrolyte and cathode materials should also be considered in order to attain both long-term stability and cycling. In this work the analysis of structural, electrical, and thermal properties of simple and layered cobaltites (GdBaCo2O5 + δ, NdBaCo2O5 + δ, Ba0.5Sr0.5CoO3–δ, Y0.8Ca0.2BaCo4O7 + δ), cobaltite-ferrites (NdBa0.5Sr0.5Co1.5Fe0.5O5 + δ, GdBaCoFeO5 + δ, Ba0.5Sr0.5Co0.8Fe0.2O3–δ, Ba0.5Sr0.5Co0.2Fe0.8O3–δ, La0.6Sr0.4Co0.2Fe0.8O3), nikelites (La2NiO4 + δ and its alkali earth element substituted derivatives) and nikelate (LaNi0.6Fe0.4O3–δ) was investigated in terms of their perspective applications in intermediate-temperature SOFCs based on proton-conducting electrolytes.

Correction: CO2-promoted hydrogen production in a protonic ceramic electrolysis cell

Correction for ‘CO2-promoted hydrogen production in a protonic ceramic electrolysis cell’ by Nikolay Danilov et al., J. Mater. Chem. A, 2018, 6, 16341–16346.

CO2-promoted hydrogen production in a protonic ceramic electrolysis cell

A novel solid oxide electrolysis cell based on high-performance and CO2-tolerant materials, a BaCe0.3Zr0.5Dy0.2O3−δ proton-conducting electrolyte and a Nd1.95Ba0.05NiO4+δ oxygen electrode, was successfully fabricated and tested. Unusual characteristics leading to enhanced improvement were observed for this cell when the reducing atmosphere was enriched with CO2. A possible mechanism by which this behaviour may be explained is proposed.