GDC Phase Research Articles

Combustion synthesis of NiO–Ce0.9Gd0.1O1.95 nanocomposite anode and its electrical characteristics of semi-cell configured SOFC assembly

NiO–Ce0.9Gd0.1O1.95 (NiO–10GDC) nanocomposite anode material was synthesized through combustion technique for possible low temperature solid oxide fuel cells (LT–SOFCs). A low weight loss is seen in the TG/DTA thermogram that indicates the complete combustion of the reactant mixtures. The powder X-ray diffraction patterns showed that the presence of NiO, GDC and Ni crystallite phases in the as combusted product. Upon calcination at 600°C, the metallic Ni oxidized to NiO. TEM images showed a wide size distribution of fine spherical GDC and large irregularly shaped NiO particles. This NiO–10GDC anode material was applied over GDC electrolyte as a porous thin layer. Using this surface engineered GDC electrolyte a semi-cell (electrode/electrolyte structure) was fabricated. The electrical conductivity of the semi-cell was characterized with respect to temperature.

Effect of Pd-impregnation on performance, sulfur poisoning and tolerance of Ni/GDC anode of solid oxide fuel cells

Sulfur tolerance of Ni/Gd2O3–CeO2 (Ni/GDC) anodes promoted by impregnated palladium nanoparticles is investigated using the electrochemical impedance spectroscopy (EIS) and galvanostatic polarization techniques in the H2–H2S fuels at 800 °C. The anodes are alternately polarized in pure H2 and H2S-containing H2 fuels with H2S concentration gradually increased from 5 to 700 ppm at 200 mA cm−2. The degradation in performance for the hydrogen oxidation in H2S-containing H2 fuels especially at low H2S concentration is substantially smaller on Pd-impregnated Ni/GDC cermet anodes, as compared to that on pure Ni/GDC anodes. The potential of Pd-impregnated Ni/GDC electrodes measured in pure H2 decreases by 0.07 V after exposure to H2S-containing H2 fuels, substantially smaller than 0.13 V observed on pure Ni/GDC anodes under identical test conditions. The results show that Pd impregnation significantly enhances the sulfur tolerance of Ni/GDC cermet anodes particularly in the low H2S concentration range (e.g., <100 ppm). The results indicate that the enhanced sulfur tolerance of Pd impregnated Ni/GDC anodes is most likely due to the promotion effect of impregnated Pd nanoparticles on the hydrogen dissociation and diffusion processes. The reduced moderation of the morphology and microstructure of the anodes in the presence of Pd nanoparticles may be the result of weaker interaction or adsorption of sulfur on Ni and GDC phases.

High-performance Gd0.2Ce0.8O2-impregnated LaNi0.6Fe0.4O3−δ cathodes for intermediate temperature solid oxide fuel cell

High-performance LaNi0.6Fe0.4O3−δ (LNF) cathode for intermediate temperature solid oxide fuel cell is fabricated by the ion impregnation of oxygen ion conducting Gd-doped ceria (GDC, Gd0.2Ce0.8O2). The microstructure of the GDC-impregnated LNF cathode is characterized by the dispersion of nano-sized GDC particles in the LNF porous framework. The particle size of the impregnated GDC phase is in the range of 40–50nm. Uniform distribution of the nano-sized ionic conducting GDC phase significantly enhances the cathode activities for the O2 reduction reaction. In the case of the 21.3wt.% GDC-impregnated LNF cathode, the specific polarization resistance (Rp) is 0.13Ωcm2 at 750°C, a reduction by 81.43% compared with that of the pure LNF cathode at the same temperature. The results indicate that GDC impregnation has significant electrocatalytic effect on the O2 reduction reactions on the LNF cathodes. The improved performance of GDC-impregnated LNF cathode is attributed to the extended triple-phase boundary (TPB) and enhanced oxide ion conductivity.

Preparation of Nanocomposite GDC/LSCF Cathode Material for IT-SOFC by Induction Plasma Spraying

Homogeneous mixtures of Ce0.8Gd0.2O1.9 (GDC) and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) nanopowders were successfully synthesized using induction plasma by axial injection of a solution. The resulting nanocomposite powders consisted of two kinds of nanopowders with different mass ratio of GDC/LSCF, such as 3/7 and 6/4. The morphological features, crystallinity, and the phases of the synthesized powders were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), local energy-dispersive x-ray spectroscopy (EDS) analysis, and x-ray diffraction (XRD). The nanopowders are almost globular in shape with a diameter smaller than 100 nm and their BET specific areas are around 20 m2 g−1. The GDC and LSCF phases are well distributed in the nanopowders. In addition, suspensions, made with the as-synthesized composite nanopowders and ethanol, were used to deposit cathode coatings using suspension plasma spray (SPS). Micro-nanostructures of the coatings are discussed. The coatings are homogeneous and porous (51% porosity) with cauliflower structures.

Effect of Ni-GDC AFL Composition on Performance of IT-SOFCs

Anode supported solid oxide fuel cells (SOFCs) with various NiO content in the anode function layer (AFL) were fabricated and investigated. For AFLs with lower NiO content, the observed open circuit potential was higher. However, the highest maximum power density of 1.15 W/cm2 at 650 °C was achieved at 60 wt% of NiO in the AFL, which is a 1:1 volume ratio of Ni to GDC phase. The optimal composition was valid in the intermediate temperature range from 450 to 650 °C. The effect of the optimal composition on power density was retained for 200 hours with high power density of 1.1 W/cm2. Electrochemical impedance tests supported this result by showing the lowest electrode area specific resistance at 60 wt% NiO, which has a linear relationship with maximum power density.

A comparative study of H 2S poisoning on electrode behavior of Ni/YSZ and Ni/GDC anodes of solid oxide fuel cells

The effect of sulfur poisoning on the activity and performance of Ni/Y 2O 3–ZrO 2 (Ni/YSZ) and Ni/Gd 2O 3–CeO 2 (Ni/GDC) cermet anodes of solid oxide fuel cells has been examined by polarization and electrochemical impedance spectroscopy (EIS) measurements at 800 °C. The anodes are alternately polarized in pure H 2 and H 2S-containing H 2 fuels with H 2S concentration gradually increased from 5 ppm to 700 ppm at 200 mA cm −2 for 2 h. The results show that the anode potential of Ni/YSZ electrodes measured in pure H 2 decreases from 0.61 V to 0.34 V after exposure to H 2S-containing H 2 fuels with H 2S concentration increased from 5 to 700 ppm. On the other hand, the anode potential of Ni/GDC electrodes measured in pure H 2 decreases from 0.78 V to 0.72 V under identical test conditions. The degradation in performance for the hydrogen oxidation in H 2S-containing H 2 fuels is substantially smaller on Ni/GDC anodes, as compared to that on Ni/YSZ anodes. Similar trend is also observed for the change of the electrode polarization resistance for the hydrogen oxidation reaction on the Ni/YSZ and Ni/GDC anodes after exposure to H 2S-containing H 2 fuels. The SEM results indicate the structure modification of Ni/YSZ anodes only occurs on Ni particles, and in the case of Ni/GDC anodes, structural modification on both Ni and GDC phases occurs. The mixed ionic and electronic conductivity of GDC phase could be the primary reason for the high sulfur tolerance of the Ni/GDC cermet anodes.

Improvement of electrochemical performance of anode-supported SOFCs by NiO–Ce 0.9Gd 0.1O 1.95 nanocomposite powders

In this study, NiO–Ce 0.9Gd 0.1O 1.95 (NiO–GDC) nanocomposite powders were synthesized by hydroxide co-precipitation method, and applied to improve the microstructure of solid oxide fuel cell (SOFC) anodes. The NiO–GDC anodes prepared from the NiO–GDC nanocomposite powders showed uniform microstructure with uniform distribution of NiO and GDC phases. Due to the uniform phase distribution, the Ni–GDC anodes prepared from the NiO–GDC nanocomposite powders had longer triple phase boundary (TPB), which resulted in enhanced electrochemical reactions. The anode-supported SOFC fabricated from the co-precipitated NiO–GDC nanocomposite powders exhibited higher electrochemical performance than the anode-supported SOFC fabricated from the mechanically mixed NiO–GDC nanopowders. The experimental results show that the use of the Ni–GDC anodes with uniform microstructure can effectively improve the electrochemical performance of anode-supported SOFC.

(La 0.74Bi 0.10Sr 0.16)MnO 3− δ–Ce 0.8Gd 0.2O 2− δ cathodes fabricated by ion-impregnating method for intermediate-temperature solid oxide fuel cells

Porous composite cathodes were fabricated by impregnating (La 0.74Bi 0.10Sr 0.16)MnO 3− δ (LBSM) electronic conducting structure with the ionic conducting Ce 0.8Gd 0.2O 2− δ (GDC) phase. The ion impregnation of the GDC phase significantly enhanced the electrocatalytic activity of the LBSM electrodes for the O 2 reduction reactions, and the ion-impregnated LBSM–GDC composite cathodes showed excellent performance. At 700 °C, the value of the cathode polarization resistance (Rc) was only 0.097 Ω cm 2 for an ion-impregnated LBSM–GDC cathode, and the performance was gradually improved by increasing the loading of the impregnated GDC. For the performance testing of single cells, the maximum power density was 1036 mW cm −2 at 700 °C for a cell with the LBSM–GDC cathode. The results demonstrated the unique combination of the LBSM electronic conducting structure with high ionic conducting GDC phase was a valid method to improve the electrode performance, and the ion-impregnated LBSM–GDC was a promising composite cathode material for the intermediate-temperature solid oxide fuel cells.

Fabrication and Performance of GDC-Impregnated ( La , Sr ) MnO3 Cathodes for Intermediate Temperature Solid Oxide Fuel Cells

High-performance (LSM) cathodes for intermediate temperature solid oxide fuel cells were fabricated by the ion impregnation of oxygen ion conducting Gd-doped (GDC) oxide. The microstructure of the GDC-impregnated LSM electrode was characterized by the uniform dispersion of very fine GDC particles in the LSM porous framework. The particle size of the impregnated GDC phase was in the range of . Uniform distribution of the nanosized ionic conducting GDC phase significantly enhanced the electrode activities for the reduction reaction. In the case of the GDC-impregnated LSM electrode, electrode polarization resistance was at , 56 times lower than that of the pure LSM at the same temperature. GDC-impregnated LSM electrode showed lower activation energy and low reaction order with respect to the partial pressure of oxygen, as compared to that on the pure LSM electrodes. The results indicate that GDC impregnation has significant electrocatalytic effect on the reduction reactions on the LSM electrodes.

Preparation and Oxygen Permeability of Gd-Doped Ceria and Spinel-Type Ferrite Composites

ABSTRACTThe preparation and oxygen permeability of composites of Ce0.8Gd0.2O2-ö (GDC) and spinel-type ferrites, MFe2O4 (M = Co and Mn) have been investigated. The composites of GDC -x vol% MFe2O4, where x ranged from 5 to 65, were prepared by a citrate-based liquid-mix technique. The composites were found to be almost fully densified by sintering at 1300 °C for 2 h. From TEM observations, the grain size of GDC and spinel-type phases was found to be less than 0.5 μm. In the case of M = Co, GDC - 25 vol% CoFe2O4 with a membrane thickness of 1.0 mm exhibited an oxygen flux density of 0.21 μmol·cm-2·s-1 under the P(O2) difference between He (20 sccm) and air at 1000 °C. Under reducing atmosphere of Ar-5%H2, the oxygen flux density of this composite increased up to 1.3 μmol·cm-2·s-1. Moreover, under Ar-10%CH4 gas flow, GDC - 15 vol% MnFe2O4 with a membrane thickness of 0.24 mm exhibited the oxygen flux density of 2 and 7 μmol·cm- · s- at 800 and 1000 °C, respectively.