Obtaining high power density at low operating temperatures has been an ongoing challenge in solid oxide fuel cells (SOFC), which are efficient engines to generate electrical energy from fuels. Here we report successful demonstration of a thin-film three-dimensional (3-D) SOFC architecture achieving a peak power density of 1.3 W/cm(2) obtained at 450 °C. This is made possible by nanostructuring of the ultrathin (60 nm) electrolyte interposed with a nanogranular catalytic interlayer at the cathode/electrolyte interface. We attribute the superior cell performance to significant reduction in both the ohmic and the polarization losses due to the combined effects of employing an ultrathin film electrolyte, enhancement of effective area by 3-D architecture, and superior catalytic activity by the ceria-based interlayer at the cathode. These insights will help design high-efficiency SOFCs that operate at low temperatures with power densities that are of practical significance.
Structural and microstructural properties as well as the fuel cell performance of anhydrous proton conducting yttria-doped barium zirconate (BYZ) membranes were investigated. The membranes were nominally about 100 nm thick and were fabricated by both atomic layer deposition (ALD) and pulsed laser deposition (PLD) techniques on micromachined Si substrates. Electrochemical cells (H 2 , Pt/BYZ/Pt, air) were fabricated using porous platinum electrodes deposited by sputtering. The cells were tested in the temperature regime 200-450 °C. Power densities of 136 mW/cm 2 at 400 °C employing a BYZ membrane fabricated by ALD and 120 mW/cm 2 at 450 °C employing a BYZ fabricated by PLD clearly represent the highest reported values in the literature at these temperatures. The difference in the cell performances for the ALD BYZ versus PLD BYZ membranes is attributed to differences in their surface morphology and interfacial microstructure.
This feature article provides a progress review of atomic layer deposition (ALD) for fabrication of oxide-ion as well as proton conducting ceramic fuel cells. A comprehensive analysis of structural, chemical, surface kinetics, and electrochemical characterization results of ALD membranes is also presented. ALD is a surface reaction limited method of depositing conformal, high quality, pinhole-free, uniform thickness nanofilms onto planar or three-dimensional structures. Deposition by one atomic layer at a time also affords unprecedented opportunities to engineer surface termination, to form compositionally graded structures or graded doping, and to synthesize metastable phases that cannot be realized otherwise. Indeed, thin ceramic electrolyte membranes made by ALD exhibit enhanced surface exchange kinetics, reduced ohmic losses, and superior fuel cell performance as high as 1.34 W cm À2 at 500 C. More importantly, ALD offers the opportunity to design and engineer surface structures at the atomic scale targeting improved performance of not only ceramic fuel cells, but also electrochemical sensors, electrolysers and pumps. Joon Hyung Shim is an Assistant Professor of Mechanical Engineering at Korea University (KU) and a Project Manager of Green Manufacturing Research Center (GMRC) at KU. Before joining KU as a faculty, he worked as a postdoctoral researcher at National Renewable Energy Laboratory (NREL) and a fulltime lecturer of Mechanical Engineering at Stanford University. He received the B.S. degree in Mechanical and Aerospace Engineering from Seoul National University in 2002. He also received the M.S. and Ph.D. degree in Mechanical Engineering from Stanford University in 2004 and 2009 respectively. Sangkyun Kang is an executive managing director of Hanchang Industries, where he oversees researches in energy materials. Before joining Hanchang Industries, he worked as a research staff member of Samsung Advanced Institute of Technology. There, he conducted ALD research as the leader of the thin lm ceramic fuel cell project. He
This study presents atomic scale characterization of grain boundary defect structure in a functional oxide with implications for a wide range of electrochemical and electronic behavior. Indeed, grain boundary engineering can alter transport and kinetic properties by several orders of magnitude. Here we report experimental observation and determination of oxide-ion vacancy concentration near the Σ13 (510)/[001] symmetric tilt grain-boundary of YSZ bicrystal using aberration-corrected TEM operated under negative spherical aberration coefficient imaging condition. We show significant oxygen deficiency due to segregation of oxide-ion vacancies near the grain-boundary core with half-width < 0.6 nm. Electron energy loss spectroscopy measurements with scanning TEM indicated increased oxide-ion vacancy concentration at the grain boundary core. Oxide-ion density distribution near a grain boundary simulated by molecular dynamics corroborated well with experimental results. Such column-by-column quantification of defect concentration in functional materials can provide new insights that may lead to engineered grain boundaries designed for specific functionalities.
High-k, low leakage thin films are crucial components for dynamic random access memory (DRAM) capacitors with high storage density and a long storage lifetime. In this work, we demonstrate a method to increase the dielectric constant and decrease the leakage current density of atomic layer deposited BaTiO3 thin films at low process temperature (250 °C) using postdeposition remote oxygen plasma treatment. The dielectric constant increased from 51 (as-deposited) to 122 (plasma-treated), and the leakage current density decreased by 1 order of magnitude. We ascribe such improvements to the crystallization and densification of the film induced by high-energy ion bombardments on the film surface during the plasma treatment. Plasma-induced crystallization presented in this work may have an immediate impact on fabricating and manufacturing DRAM capacitors due to its simplicity and compatibility with industrial standard thin film processes.
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