Design and Synthesis of Oriented Guest-Host Nanostructures for Enhanced Membrane Performances Page: 1 of 5
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Final Report Project Number: 3210-2123
Design and Synthesis of Oriented Guest-Host Nanostructures
For Enhanced Membrane Performances
Michael Z. Hul, Valmor de Almeida, Igor Kosacki,2 Douglas A. Blom,2 and E. Andrew Payzant2
1Nuclear Science and Technology Division
2Metals and Ceramics Division
This project has demonstrated a novel nanomaterial design concept and a synthesis method for "guest-
host" type superionic-conducting nanocomposite membranes. This concept consists of nanophases of
oxide electrolyte nanograins (guest) encapsulated inside the nanopore channels of an oxide layer matrix
(host), with channels oriented perpendicular to the layer surface. Using ionic conducting YSZ (yttrium
stabilized zirconia) as a special case, we have shown that the host-guest design allows orientation of a
large number channels, allowing a high density of of nanograin boundaries/interfaces to be built into the
film to enhance cross-membrane conductivity. This structure allowed conductivity measurements with
impedance spectroscopy to be performed for the first time at room temperature. Cross-membrane
conductivity values at low temperature ranges of interest are the higher than any reported values. The
conductivity-enhancing mechanisms could be attributed to (1) controlled orientation and increased
number density of YSZ nanograin-host interfaces and (2) creation and stabilization of YSZ
nanocrystalline phases inside nanopore channels (<10 nm dia.). This successful initial demonstration of
host-guest nanostructures is expected to have direct impact on fuel cell technologies, and may also have
beneficial use in a broad range of applications such as in solar cells, sensors, chemical/gas separations,
catalysis, and magnetic memory devices. This work may also lead to a new way to develop membrane
technologies that offer orders-of-magnitude higher permeability and selectivity, as well as improved
thermal stability of the desirable nanocrystalline phases.
Oxide ionic conductors, such as oxygen- or proton-conducting ceramic membranes, are very important
materials for a wide range of applications, such as in fuel cells, microbatteries, and other solid-state
ionics-based devices. Solid oxide fuel cells (SOFCs) present an efficient and ecologically acceptable way
to simultaneously generate heat/electricity with theoretical efficiency as high as 70%. One future
development goal is to introduce intermediate-temperature solid oxide fuel cells (IT-SOFCs) by
considering alternative materials (such as electrolyte and electrode) that would enable lowering the
operating temperature from 1000 C to below 800 C without loss of performance. Lower-temperature
operation will reduce the system materials requirement and cost, and also avoid many undesirable
interfacial reactions between electrode and electrolyte materials. At low operating temperatures, superior
ionic conductivity of the oxide electrolyte layer (> 102 S/cm) is required for success in fuel cell
applications. A technical challenge lies in the creation of a stable membrane nanostructure that offers
cross-membrane conductivity far above what is available today.
Nanomaterials have been considered promising in improving materials performance for solid-state ionics
and SOFCs. The objectives of this project are to:
1. Demonstrate that novel host-guest nanocomposite membrane can be synthesized,
2. Prove that the designed nanostructure (i.e., large number density of oriented guest-host interfaces and
nanocrystalline grain boundaries) can enhance cross-membrane ionic conductivity, and
3. Demonstrate improved thermal stability of nanocrystalline phases due to host nanopore confinement.
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Hu, M.Z. Design and Synthesis of Oriented Guest-Host Nanostructures for Enhanced Membrane Performances, report, November 15, 2005; [Tennessee]. (digital.library.unt.edu/ark:/67531/metadc892710/m1/1/: accessed October 20, 2018), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.