Nikolay Danilov

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.

Electrochemical Approach for Analyzing Electrolyte Transport Properties and Their Effect on Protonic Ceramic Fuel Cell Performance

The design and development of highly conductive materials with wide electrolytic domain boundaries are among the most promising means of enabling solid oxide fuel cells (SOFCs) to demonstrate outstanding performance across low- and intermediate-temperature ranges. While reducing the thickness of the electrolyte is an extensively studied means for diminishing the total resistance of SOFCs, approaches involving an improvement in the transport behavior of the electrolyte membranes have been less-investigated. In the present work, a strategy for analyzing the electrolyte properties and their effect on SOFC output characteristics is proposed. To this purpose, a SOFC based on a recently developed BaCe0.5Zr0.3Dy0.2O3-δ proton-conducting ceramic material was fabricated and tested. The basis of the strategy consists of the use of traditional SOFC testing techniques combined with the current interruption method and electromotive force measurements with a modified polarization-correction assessment. This allows one to determine simultaneously such important parameters as maximal power density; ohmic and polarization resistances; average ion transport numbers; and total, ionic, and electronic film conductivities and their activation energies. The proposed experimental procedure is expected to expand both fundamental and applied basics that could be further adopted to improve the technology of electrochemical devices based on proton-conducting electrolytes.

The effect of oxygen and water vapor partial pressures on the total conductivity of BaCe0.7Zr0.1Y0.2O3–δ

The effect of oxygen and water vapor partial pressure on the total conductivity of the proton-conducting BaCe0.7Zr0.1Y0.2O3–δ material is investigated in the present work. Single-phase and dense ceramic materials have been successfully obtained using the citrate–nitrate synthesis method. The contributions of partial conductivities (hole, oxygen-ionic, protonic) are evaluated based on electrical and emf measurements. At 900xa0°C in air atmosphere, ionic and hole conductivities almost equivalently contribute to the total conductivity, while in reducing temperatures, the transport of the studied material becomes ionic; the predominant protonic transport (tHxa0≈xa01) realizes under wet hydrogen atmospheres at temperatures below 700xa0°C. Based on the measurements of total conductivity as a function of water vapor partial pressure, it is found that the increase of conductivity in reducing atmospheres is associated with the growth of proton conductivity. A non-monotonic change of total conductivity in oxidizing atmospheres is caused by the competing effects, namely decreasing the hole conductivity and increasing the protonic one.

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.