Intermediate Solid Oxide Fuel Cells Research Articles

Doping strategy on improving the overall cathodic performance of double perovskite LnBaCo2O5+δ (Ln=Pr, Gd) as potential SOFC cathode materials

A series of single-phase double perovskite Pr1-xGdxBaCo2-yFeyO5+δ (x = 0, 0.5 and 1, 0 ≤ y ≤ 1) materials were engineered through A/B site co-doping strategy to improve the mechanical, electrical and electrochemical properties as potential cathode materials for the application of intermediate solid oxide fuel cells (IT-SOFCs). The corresponding thermochemical stability, thermal expansion behavior, electrical conductivity and cathodic polarization resistance of the materials were systematically investigated. It was found that the A-site dual lanthanide doped Pr0.5Gd0.5BaCo2O5+δ (PGBCO) exhibits improved electrical conductivity, reduced thermal expansion, and comparatively low electrochemical polarization resistance versus single lanthanide double perovskite, PrBaCo2O5+δ (PBCO) and GdBaCo2O5+δ (GBCO) materials. Further investigation on the effect of B-site Fe-doping on Pr0.5Gd0.5BaCo2-yFeyO5+δ (PGBCF-y, 0 ≤ y ≤ 1) reveals that all the PGBCF-y compositions exhibit excellent chemical stability with Gd-doped ceria (GDC) at operating temperatures not higher than 1 100 °C. Besides, doping of Fe in B-site can effectively reduce the thermal expansion coefficients (TECs) of the Pr0.5Gd0.5BaCo2O5+δ ceramics at 30–1 000 °C. And the electrochemical impedance spectra (EIS) results show that the PGBCF-y|GDC| PGBCF-y symmetric cells have acceptable low area specific polarization resistances. Further examination of the cathodic polarization and characteristic capacitance from the AC impedance spectra by employing the relaxation time distribution (DRT) method demonstrated that charge transfer is the dominating sub-process for the oxygen transport through the materials.

Structure, thermal expansion and electrical conductivity of La2–xGdxNiO4+δ (0.0 ≤x≤ 0.6) cathode materials for SOFC applications

A new series of La2–xGdxNiO4+δ (0.0 ≤ x ≤ 0.6) synthesized via formate pyrolysis were tested as potential cathode materials for intermediate solid oxide fuel cells (IT-SOFCs). It was found that the materials are single-phase up to x = 0.5 and crystallize in a tetragonal structure (I4/mmm space group). They show superior oxygen over-stoichiometry values, δ, to those of both the undoped lanthanum nickelate and the one doped with alkali-earth elements. To satisfy the requirements for the increased efficiency and durability of SOFCs, chemical and thermo-mechanical compatibility between the cathode materials developed and a Ce0.8Gd0.2O1.9 solid-state electrolyte was studied. Concentration dependences of electrical and thermal properties of the La2–xGdxNiO4+δ compounds were discussed in interrelation with their structural peculiarities and the temperature behavior of δ.

Electrochemical characteristics of La 0.6 Sr 0.4 Co 1−y Fe y O 3 (y=0.2–1.0) fiber cathodes

Abstract Electrospun La x Sr 1−x Co 1−y Fe y O 3 (LSCF) fibers with y=0.2 – 1.0 have been investigated as the cathode of intermediate solid oxide fuel cells (IT-SOFC). The electrochemical performances of LSCF (y=0.2–1.0) fibers were studied by impedance spectroscopy in symmetrical cells containing gadolinium doped ceria (CGO) electrolyte and LSCF electrode infiltrated with CGO. Impedance measurements showed that the impedance spectra have two or three semicircles, depending on the measurement temperature. The LSCF electrodes with higher cobalt content exhibit lower polarization resistance (R p ) and the La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 electrode displayed the lowest polarization resistance between 500 and 900 °C, classifying this composite cathode as a promising material for intermediate temperature SOFC based on CGO electrolyte.

La 2NiO 4+ δ potential cathode material on La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 electrolyte for intermediate temperature solid oxide fuel cell

La 2NiO 4+ δ , a mixed ionic-electronic conducting oxide with K 2NiF 4 type structure, has been studied as cathode material with La 0.9Sr 0.1Ga 0.8Mg 0.2O 2.85 (LSGM) electrolyte for intermediate solid oxide fuel cells (IT-SOFCs). XRD results reveal excellent chemical compatibility between the La 2NiO 4+ δ sample and LSGM electrolyte. A single cell (0.22 cm 2 active area) was fabricated with La 2NiO 4+ δ as cathode, Ni–Sm 0.2Ce 0.8O 1.9 (2:1; w/w) as anode and LSGM as electrolyte. A thin buffer layer of Sm 0.2Ce 0.8O 1.9 (SDC) between anode and electrolyte was used to avoid possible interfacial reactions. The cell was tested under humidified H 2 and stationary air as fuel and oxidant, respectively. The electrochemical behaviour was evaluated by means of current–voltage curves and impedance spectroscopy. Microstructure and morphology of the cell components were analysed by SEM-EDX after testing. The maximum power densities were 160, 226, and 322 mW cm −2 at 750, 800 and 850 °C, respectively with total polarisation resistances of 0.77, 0.48 and 0.31 Ω cm 2 at these temperatures. Cell performance remained stable when a current density of 448 mA cm −2 was demanded for 144 h at 800 °C, causing no apparent degradation in the cell. The performance of this material may be further improved by reducing the electrolyte thickness and optimisation of the electrode microstructure.

Comparison between Ni–Rh/gadolinia doped ceria catalysts in reforming of propane for anode implementations in intermediate solid oxide fuel cells

Steam and autothermal reforming of propane over Ni–Rh/GDC catalysts prepared by coprecipitation and by Pechini method were investigated in the temperature range 873–1073 K. The weight ratio for Ni, Rh and Ce 0.8Gd 0.2O 2 (45:5:50) and the operating temperatures were chosen in order to gain propaedeutical information on fuel reactivity under typical intermediate solid oxide fuel cell (IT-SOFC) operating conditions. The Pechini synthesis allows to obtain catalysts with lower surface area, smaller nickel crystallites and a bimodal distribution of rhodium in comparison to the coprecipitation method. Despite the different methods of synthesis lead to catalysts with different morphological and structural properties, the activity of catalysts is quite similar. At reaction temperature higher than 973 K, under both steam reforming (SR) and autothermal reforming (ATR), the catalysts show high propane conversion and syngas (H 2 + CO) productivity. Deactivation of catalysts was observed at 873 and 973 K under SR conditions due to coke formation. In ATR, coke formation was almost completely depressed and the catalysts resulted to be very stable even at low reaction temperature (873 K). In SR coke formation occurs with higher rate on the catalyst having higher Ni dispersion, probably since propane cracking reaction is the pre-eminent phenomenon in promoting coke formation.

Intermediate Temperature Solid Oxide Fuel Cells Using LaGaO3 Electrolyte II. Improvement of Oxide Ion Conductivity and Power Density by Doping Fe for Ga Site of LaGaO3

Effects of small amounts of Fe doping for Ga site in oxide on oxide ion conductivity is investigated in this study. It is found that doping a small amount of Fe is effective for improving the oxide ion conductivity in (LSGM). The highest oxide ion conductivity was exhibited at x = 0.03 in among the Fe‐doped samples. Electron spin resonance (ESR) measurements suggest that Fe is trivalent in lattice. The application of the Fe‐doped oxide for the electrolyte of solid oxide fuel cell was further investigated. Power density of the solid oxide fuel cell was increased by using Fe‐doped LSGM for electrolyte. This can be explained by the decrease in electrical resistance loss by improving the oxide ion conductivity. A maximum power density close to was obtained at 1073 K on the cell using 0.5 mm thick (LSGMF) and as the electrolyte and the oxidant, respectively. Therefore, close to the theoretical open‐circuit potential was exhibited by the LSGMF cell. On the other hand, the power density was slightly smaller than that of the cell using Co‐doped LSGM as electrolyte, especially, at temperatures lower than 973 K. This may result from the large activation energy for ion conductivity. However, the power density of the LSGMF cell was higher than that of the LSGM cell. Therefore, LSGM doped with a small amount of Fe is a promising electrolyte similar to Co‐doped LSGM for the intermediate solid oxide fuel cell. © 2000 The Electrochemical Society. All rights reserved.