ABSTRACT
Increasing the performance and improving the stability of solid oxide cells are critical requirements for advancing this technology toward commercial applications. In this study, a systematic comparison of anode-supported cells utilizing thin films with those utilizing conventional screen-printed yttria-stabilized zirconia (YSZ) is performed. High-resolution secondary ion mass spectrometry (SIMS) imaging is used to visualize, for the first time, the extent of Ni diffusion into screen-printed microcrystalline YSZ electrolytes of approximately 2-3 µm thickness, due to the high temperature (typically >1300 °C) used in the conventional sintering process. As an alternative approach, dense YSZ thin films and Ni(O)-YSZ nanocomposite layers are prepared using pulsed laser deposition (PLD) at a relatively low temperature of 750 °C. YSZ thin films exhibit densely packed nanocrystalline grains and a remarkable suppression of Ni diffusion, which are further associated with some reduction in the ohmic resistance of the cell, especially in the low temperature regime. Moreover, the use of a Ni-YSZ nanocomposite layer resulted in improved contact at the YSZ/anode interface as well as a higher density of triple phase boundaries due to the nanoscale Ni and YSZ grains being homogeneously distributed throughout the structure. The cells utilizing the YSZ/Ni-YSZ bilayer thin films show excellent performance in fuel cell operation and good durability in short-term operation up to 65 hours. These results provide insights into ways to improve the electrochemical performance of SOCs by utilizing innovative thin film structures in conjunction with commercially viable porous anode-supported cells.
ABSTRACT
Solid oxide fuel cells (SOFCs) are power-generating devices with high efficiencies and considered as promising alternatives to mitigate energy and environmental issues associated with fossil fuel technologies. Nanoengineering of electrodes utilized for SOFCs has emerged as a versatile tool for significantly enhancing the electrochemical performance but needs to overcome issues for integration into practical cells suitable for widespread application. Here, we report an innovative concept for high-performance thin-film cathodes comprising nanoporous La0.6Sr0.4CoO3-δ cathodes in conjunction with highly ordered, self-assembled nanocomposite La0.6Sr0.4Co0.2Fe0.8O3-δ (lanthanum strontium cobalt ferrite) and Ce0.9Gd0.1O2-δ (gadolinia-doped ceria) cathode layers prepared using pulsed laser deposition. Integration of the nanoengineered cathode layers into conventional anode-supported cells enabled the achievement of high current densities at 0.7 V reaching ~2.2 and ~4.7 A/cm2 at 650 °C and 700 °C, respectively. This result demonstrates that tuning material properties through an effective nanoengineering approach could significantly boost the electrochemical performance of cathodes for development of next-generation SOFCs with high power output.
ABSTRACT
The electrical conductivity of nickel (2 wt %)-doped BaZr0.1Ce0.7Y0.1Yb0.1O3-δ (BZCYYb) acceptor-doped perovskite oxide was evaluated under air and a 1% H2 atmosphere. The partial conductivity was calculated from the total conductivity and the transport number of each carrier (tH+, tO2-, and th+) obtained using the concentration cell method. Its correlation with the dissolution state of the protons in the oxide as studied by in situ diffuse reflection Fourier transform infrared spectroscopy is discussed. When the concentration of protons that dissolved in BZCYYb-Ni was high, the proton partial conductivity was also high. An increase in hole conductivity in the high-temperature region in an air atmosphere was observed, suggesting that dissociation of protons strongly correlates with such a dominant carrier change. The dissociation of protons should be determined by the stability of protons in the oxide by the interaction with the lattice oxygen, and it was suggested that the dissolution state of protons can be controlled by modifying such stability in the oxide.
ABSTRACT
The effect of microstructure of Gd2O3-doped CeO2 (GDC) films on oxygen surface exchange and diffusion is reported. Epitaxial GDC (10 mol% Gd) films up to 1 µm in thickness are prepared using pulsed laser deposition on (100) yttria-stabilized zirconia single-crystal substrates and subjected to high-temperature annealing at 1300 °C in air to induce microstructural modifications. Characterization using atomic force microscopy and transmission electron microscopy reveals granular morphologies comprised of densely packed columnar nanostructures for the as-grown GDC films; however, significant microstructural reconstruction of the entire GDC layer occurs after high-temperature annealing. (18)O isotope exchange depth profiling with dynamic secondary ion mass spectroscopy is employed to evaluate the oxygen surface exchange coefficient k* and the diffusion coefficient D* at T = 600 °C. The as-grown GDC exhibits up to 10 times higher k* than the annealed film. The strong differences in oxygen surface reaction are correlated to the observed film properties including surface microstructure and cerium oxidation state as evaluated using electron energy loss spectroscopy in scanning transmission electron microscopy.
