A. K. Demin

Thermodynamic analysis of a hydrogen fed solid oxide fuel cell based on a proton conductor

Abstract In the present investigation, the thermodynamic analysis of a solid oxide fuel cell based on protonic electrolyte (SOFC(H+)) and fed with hydrogen is performed. The influence of such parameters as hydrogen purity, air humidity, hydrogen and oxygen utilization as well as working temperature on the fuel cell efficiency is established. The results obtained show that the hydrogen fed SOFC(H+) has an essential advantage as compared to the hydrogen fed SOFC based on an oxygen ion electrolyte (SOFC(O2−)) regarding the efficiency of chemical energy to electrical power transformation. It was established that the maximum SOFC(H+) efficiency in the range between 1000 and 1300 K exceeds 80%, which is significantly higher than that of the SOFC(O2−). It was also estimated that the SOFC(H+) efficiency at 1000 K is about 70% when it runs at 60% of its maximum power, whereas the practically reachable SOFC(O2−) efficiency under the above-mentioned conditions is less than 55%.

Electrical conductivity of iron-doped calcium titanate

Abstract Both total and partial electronic conductivity of iron-doped calcium titanates, of general formula CaTi 1− x Fe x O 3−δ ( x =0, 0.1,…0.5), were investigated as a function of oxygen partial pressure at high temperatures (900, 1000°C) by means of the four-probe technique and the Hebb–Wagner polarization method, respectively. The oxygen partial pressure interval extended from 1 to 10 −18 atm. Ti substitution by Fe results in a considerable increase of both ionic and electronic conductivity and in appearance of a wide region of primarily ionic conductivity, independent of the oxygen partial pressure. Of these compositions, the x =0.2 sample has the highest oxygen ion conductivity. A model of defect equilibrium is discussed.

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.

Effect of doping with Co2O3, TiO2, Fe2O3, and Mn2O3 on the properties of Ce0.8Gd0.2O2−δ

The effects of Co, Fe, Mn, and Ti oxide additions on the sinterability and crystal-chemical, thermal, and electrical properties of Ce0.8Gd0.2O2−δ have been studied. The results indicate that these oxides enhance the sinterability of the mixed oxide, regardless of whether they were introduced before or after synthesis. The most effective sintering aid is Co2O3. The lattice parameters of Ce0.8Gd0.2O2−δ samples containing different metal oxide additions (1 mol %) are refined in space group Fm3m. The temperature-dependent thermal expansion data are used to determine the linear thermal expansion coefficients of the samples. Manganese oxide additions reduce the electrical conductivity of Ce0.8Gd0.2O2−δ, whereas the other dopants increase it in the order Ti < Fe < Co. The activation energy for conduction increases in the order Co < Ti < Fe < Mn.

Formation of dense electrolytes based on BaCeO3 and BaZrO3 for application in solid oxide fuel cells: The role of solid-state reactive sintering

Methods of synthesis and formation of a high-dense ceramic prepared from barium cerate and zirconate, which is applied as electrolyte in solid oxide fuel cells, are considered in the present work. The main attention is devoted to the relatively new strategy of solid-state reactive sintering method, which consists in the introduction of small amounts of sintering additives to initial precursors. Analysis of published data on the effect of sintering additives on the physicochemical and transport properties of proton-conducting electrolytes is carried out.

Transfer phenomena in an electrochemical reactor based on mixed oxide conductor

Abstract Operation of an electrochemical reactor (ECR) for hydrogen production from steam based on the membrane having mixed oxygen ion and electronic conductivity has been considered. On the basis of the described model, one can obtain the dependence of the ECR productivity on the anode and cathode gases parameters as well as the distributions of EMF, membrane conductivity and current density over the electrochemical section of the ECR. The results for the ECR based on the CaTi0.8Fe0.2Oy membrane are presented.

Solid electrolytes based on CeO2 for medium-temperature electrochemical devices

CeO2-based solid solutions with a fluorite structure are promising materials as electrolytes of medium-temperature electrochemical devices: electrolytic cells, oxygen sensors, and solid oxide fuel cells. In this work, studies are presented of the effect of the dopant cation radius and its concentration on the physico-chemical properties of the Ce1 − xLnxO2 − δ solid solutions (x = 0–0.20; Ln = La, Nd, Sm, Eu, Gd, Dy, Ho, Er, Yb) and also of multicomponent solid solutions of Ce1 − xLnx/2Ln′x/2O2 − δ (x = 0–0.20; Ln = Sm, La, Gd and Ln′ = Dy, Nd, Y) and Ce1 − x − ySmxMyO2 − δ (M = Ca, Sr, Ba) obtained using the solid-phase synthesis technique. Electric properties of the samples were studied in the temperature range of 623–1173 K and in the oxygen partial pressure range of 0.01–10−22 MPa. The values of oxygen critical pressure

Structure and electric properties of BaCe0.77 − xZrxGd0.2Cu0.03O3 − δ

left( {p_{O_2 }^* } right)

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

are presented, at which the ionic and electron conductivity values are equal. The values were calculated on the basis of experimental dependences at 1023 K at the assumption that the ionic conductivity value is determined only by the dopant concentration and its effective ionic radius and is independent of the oxygen partial pressure.

Influence of acceptor doping on ionic conductivity in alkali earth titanate perovskites

AbsractIn the present work, samples with the composition of BaCe0.77 − xZrxGd0.2Cu0.03O3 − δ (x = 0, 0.1…0.7, 0.77) were synthesized according to the standard solid state technique. The effect of zirconium oxide on the phase character, structure, and conductivity was studied using the methods of X-ray diffraction analysis, scanning electron microscopy, and four-probe method, accordingly. Stability of these materials in the flow of carbon dioxide was studied. The results show that introduction of zirconium oxide leads to preservation of a single-phase system (x ≤ 0.6), a decrease in the grain size, and an increase in stability in the CO2 atmosphere.