Gadolinium doped ceria (GDC) (known alternatively as gadolinia doped ceria, gadolinium doped cerium oxide, cerium(IV) oxide-gadolinium doped, and GCO, formula Gd:CeO2) is a ceramic electrolyte used in solid oxide fuel cells (SOFCs). It has a cubic structure and a density of around 7.2 g/cm3 in its oxidised form. It is one of a class of ceria-doped electrolytes with higher ionic conductivity and lower operating temperatures (<700 °C) than those of yttria-stabilized zirconia, the material most commonly used in SOFCs. Because YSZ requires operating temperatures of 800-1000 °C to achieve maximal ionic conductivity, the associated energy and costs make GDC a more optimal (even "irreplaceable", according to researchers from the Fraunhofer Institute ) material for commercially viable SOFCs.
Structure and properties
Oxygen vacancies are created when gadolinium (a trivalent cation) is introduced into ceria (CeO2, with Ce in the 4+ oxidation state) or on reduction in CO or H2. The high concentration and mobility of the oxide ion vacancies results in a high ionic conductivity in this material. In addition to its high ionic conductivity CGO is an attractive alternative to YSZ as an electrolyte due to low reactivity and good chemical compatibility with many mixed conducting cathode materials. Dopant levels of Gd typically range from 10-20%. The majority of SOFC researchers and manufacturers still favor the use of YSZ over CGO due to YSZ having superior strength and because CGO will reduce at high temperature when exposed to H2 or CO.
Methods of synthesis have included precipitation, hydrothermal treatment, sol-gel, spray pyrolysis technique (SPT), combustion and nanocasting using cerium sources such as cerium nitrate, ammonium ceric nitrate  [clarification needed], cerium oxalate, cerium carbonate, cerium peroxide, and cerium hydroxide. GDC has been synthesized in such forms as powder, ink, solid solutions, discs, and nanomaterials (including nanoparticle, nanocrystals, nanopowder, and nanowires).
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