Optimization of proton conductors for application in solid oxide fuel cell technology

Application of proton-conducting ceramic membranes in various electrochemical devices (e.g. SOFCs, SOECs) is considered as highly beneficial. Because of a unique transport mechanism associated with proton movement in oxide materials, designing and optimization, as well as practical application of such proton conductors is a challenge. In this work, apart from discussion of literature data, authors’ own results are provided, which are focused on material-related issues, including development of electrolyte and electrode materials exhibiting high proton conductivity

Optimization of proton conductors for application in solid oxide fuel cell technology

Application of proton-conducting ceramic membranes in various electrochemical devices (e.g. SOFCs, SOECs) is considered as highly beneficial. Because of a unique transport mechanism associated with proton movement in oxide materials, designing and optimization, as well as practical application of such proton conductors is a challenge. In this work, apart from discussion of literature data, authors’ own results are provided, which are focused on material-related issues, including development of electrolyte and electrode materials exhibiting high proton conductivity

ReBaCo

Decrease of the operation temperature is considered as one of the most important targets in development of Solid Oxide Fuel Cells (SOFC), as it leads to considerable extension of their long-term operation and makes construction and utilization of the SOFC generators cost-effective. Relatively high value of the activation energy of the oxygen reduction reaction (ORR) occurring at the cathode, and consequently, large cathodic polarization resistance at lower temperatures is a major obstacle hindering usage of SOFCs at decreased temperatures. In this work possibility of application of manganese-doped cobalt-based cation-ordered perovskites as candidate cathode materials in the intermediate temperature (IT, ca. 600-800 °C) range is discussed. The considered oxide materials, depending on chemical composition, i.e. choice of Re element and Mn-doping level exhibit high values of mixed ionic-electronic conductivity, as well as good catalytic activity toward the oxygen reduction and moderate thermal expansion. Cathode layers manufactured on a basis of selected ReBaCo2-xMnxO5+δ oxides show low polarisation resistance

Development of novel air electrode materials for the SOFC and SOEC technologies

One of major goals in the development of solid oxide fuel cells and its reversible mode, solid oxide electrolyzer cells, is related to a decrease of the operating temperature, down to the intermediate range (600-800 °C) or even lower temperatures. However, this reduction causes an increase of the polarization resistance, especially for the air electrode, which results in a significant decline of the efficiency of the device. Therefore, it is essential to obtain new, thermally and chemically stable materials with the high ionic-electronic conductivity and good catalytic activity for the oxygen reduction reaction working in the decreased temperature range. At the same time, environmental and economic aspects have to be considered in the development of the new compounds. Promising cobalt-free electrode materials can be Cu-based oxides with the perovskite and perovskite-related structures

Influence of Doping on the Transport Properties of Y1−xLnxMnO3+δ (Ln: Pr, Nd)

It has been documented that the total electrical conductivity of the hexagonal rare-earth manganites Y0.95Pr0.05MnO3+δ and Y0.95Nd0.05MnO3+δ, as well as the undoped YMnO3+δ, is largely dependent on the oxygen excess δ, which increases considerably at temperatures below ca. 300 °C in air or O2. Improvement for samples maintaining the same P63cm crystal structure can exceed 3 orders of magnitude below 200 °C and is related to the amount of the intercalated oxygen. At the same time, doping with Nd3+ or Pr3+ affects the ability of the materials to incorporate O2, and therefore indirectly influences the conductivity as well. At high temperatures (700–1000 °C) and in different atmospheres of Ar, air, and O2, all materials are nearly oxygen-stoichiometric, showing very similar total conduction with the activation energy values of 0.8–0.9 eV. At low temperatures in Ar (δ ≈ 0), the mean ionic radius of Y1−xLnx appears to influence the electrical conductivity, with the highest values observed for the parent YMnO3. For Y0.95Pr0.05MnO3+δ oxide, showing the largest oxygen content changes, the recorded dependence of the Seebeck coefficient on the temperature in different atmospheres exhibits complex behavior, reflecting oxygen content variations, and change of the dominant charge carriers at elevated temperatures in Ar (from electronic holes to electrons). Supplementary cathodic polarization resistance studies of the Y0.95Pr0.05MnO3+δ electrode document different behavior at higher and lower temperatures in air, corresponding to the total conduction characteristics

Peculiar Properties of Electrochemically Oxidized SmBaCo2−xMnxO5+δ (x = 0; 0.5 and 1) A-Site Ordered Perovskites

Fully-stoichiometric SmBaCo2-xMnxO6 oxides (x = 0, 0.5, 1) were obtained through the electrochemical oxidation method performed in 1 M KOH solution from starting materials having close to equilibrium oxygen content. Cycling voltammetry scans allow us to recognize the voltage range (0.3–0.55 V vs. Hg/HgO electrode) for which electrochemical oxidation occurs with high efficiency. In a similarly performed galvanostatic experiment, the value of the stabilized voltage recorded during the oxidation increased with higher Mn content, which seems to relate to the electronic structure of the compounds. Results of the iodometric titration and thermogravimetric analysis prove that the proposed technique allows for an increase in the oxygen content in SmBaCo2-xMnxO5+δ materials to values close to 6 (δ ≈ 1). While the expected significant enhancement of the total conductivity was observed for the oxidized samples, surprisingly, their crystal structure only underwent slight modification. This can be interpreted as due to the unique nature of the oxygen intercalation process at room temperature

MIEC-type ceramic membranes for the oxygen separation technology

Mixed ionic-electronic conducting ceramic membrane-based oxygen separation technology attracts great attention as a promising alternative for oxygen production. The oxygen-transport membranes should not only exhibit a high oxygen flux but also show good stability under CO2-containing atmospheres. Therefore, designing and optimization, as well as practical application of membrane materials with good CO2 stability is a challenge. In this work, apart from discussion of literature data, authors’ own results are provided, which are focused on materia - related issues, including development of electrode materials exhibiting high ionic and electronic conductivities