High Temperature Fabrication of Nanostructured Yttria-Stabilized-Zirconia (YSZ) Scaffolds by <em>In Situ</em> Carbon Templating Xerogels

Abstract

We demonstrate a method for the high temperature fabrication of porous, nanostructured yttria-stabilized-zirconia (YSZ, 8 mol% yttria - 92 mol% zirconia) scaffolds with tunable specific surface areas up to 80 m·g. An aqueous solution of a zirconium salt, yttrium salt, and glucose is mixed with propylene oxide (PO) to form a gel. The gel is dried under ambient conditions to form a xerogel. The xerogel is pressed into pellets and then sintered in an argon atmosphere. During sintering, a YSZ ceramic phase forms and the organic components decompose, leaving behind amorphous carbon. The carbon formed in situ serves as a hard template, preserving a high surface area YSZ nanomorphology at sintering temperature. The carbon is subsequently removed by oxidation in air at low temperature, resulting in a porous, nanostructured YSZ scaffold. The concentration of the carbon template and the final scaffold surface area can be systematically tuned by varying the glucose concentration in the gel synthesis. The carbon template concentration was quantified using thermogravimetric analysis (TGA), the surface area and pore size distribution was determined by physical adsorption measurements, and the morphology was characterized using scanning electron microscopy (SEM). Phase purity and crystallite size was determined using X-ray diffraction (XRD). This fabrication approach provides a novel, flexible platform for realizing unprecedented scaffold surface areas and nanomorphologies for ceramic-based electrochemical energy conversion applications, e.g. solid oxide fuel cell (SOFC) electrodes.

Enhancing Activity, Charge Transport, Power Production, and Stability of Commercial Solid Oxide Fuel Cells with Yttria-Stabilized Zirconia Nanoparticles

“…Material preparation.-NanoYSZ was generated via an in situ carbon templating processing method, which has also been shown to generate ultra-high surface area particles for other SOFC relevant mixed-metal-oxides including GDC, LSCF, and strontium titanate. [17][18][19][20] The in situ carbon templating method involves two steps. First, a hybrid inorganic-organic material containing stoichiometric amounts of metal components of the desired mixed-metaloxide is heat treated at 850 °C-1350 °C in an inert atmosphere such as nitrogen or argon.…”

“…This method produces high surface area mixedmetal-oxides by heating hybrid inorganic-organic materials to 850 °C-1350 °C in nitrogen or argon followed by oxidation at 700 °C in air. [17][18][19] As stated previously, nanoYSZ is a pure oxygen ion conductor and has virtually no electrocatalytic activity for the oxygen reduction reaction. Similar to reports on infiltrated MIECs, the addition of nanoYSZ lowered the cathode reaction impedance by 40%.…”

Processing Nano-YSZ in Solid Oxide Fuel Cells: The Effect of Sintering Atmosphere on Thermochemical Stability

“…YSZ-Propylene Oxide-Glucose (YSZ-POG) hybrid materials were prepared following the same procedure that was used in our previously reported works. [1][2][3][4] Briefly, stoichiometric amounts of ZrCl 4 (99.5+%, Alfa Aesar), Y(NO 3 ) 3 •6H 2 O (99.9%, Alfa Aesar), and glucose (≥ 99.9%, Alfa Aesar) were sequentially dissolved in deionized water and magnetically stirred until complete dissolution. Propylene Oxide (PO, ≥ 99.5%, Sigma-Aldrich) was then added to the solution and stirred for about five minutes, after which a translucent yellow gel formed.…”

“…We recently developed a processing method that produces high surface area mixed-metal-oxides (up to 99 m 2 • g −1 ) in the 850 • C-1350 • C temperature range. [1][2][3][4] The processing method is referred to as the in situ carbon templating method and has been shown to work for numerous ceramics used in solid oxide fuel cell (SOFC) electrodes, including yttria-stabilized zirconia (YSZ), gadolinia-doped ceria (GDC), lanthanum-strontium-cobalt-iron-oxide (LSCF), and strontium titanate (STO). The in situ carbon templating method involves two steps.…”

“…In the second step, the amorphous carbon is burned away at 700 • C in air, a temperature low enough to preserve the ceramic nanoparticles. We have shown that the processing method works for two hybrid materials: (1) propylene oxide gels with a glucose additive to vary the carbon template concentration [1][2][3][4] and (2) citric acid gels; the carbon template concentration is controlled by the concentration of citric acid. 3,4 We have also shown that the surface area of nano-YSZ prepared with this approach is still high after 2000 hours at 500 • C (65 m 2 • g −1 ) and 700 • C (35 m 2 • g −1 ).…”