Enhanced ionic conductivity in oxide heterostructures
- Universidad Complutense, Spain
- ORNL
- Universidad Politecnica de Madrid, Spain
Fuel cells are electrochemical devices used to generate energy out of hydrogen. In a fuel cell, two conducting electrodes are separated by an electrolyte that is permeable to ions (either hydrogen or oxygen, depending on the fuel-cell category) but not to electrons. An electrode catalytic process yields the ionic species, which are transported through the electrolyte, while electrons blocked by the electrolyte pass through the external circuit. Polymeric membrane (PEMFC) or phosphoric acid fuel cells (PAFC) operating at low temperatures are the preferred option for transportation because of their quite large efficiencies (50%), compared with gasoline combustion engines (25%). Other uses are also being considered, such as battery replacements for personal electronics and stationary or portable emergency power. Solid-oxide fuel cells (SOFCs), operating at high temperatures, are a better option for stationary power generation because of their scalability. Here O{sup 2-} ions are the mobile species that travel at elevated temperatures (800-1000 C) through a solid electrolyte material to react with H{sup +} ions in the anode to produce water (Fig. 1). The high operating temperatures of solid oxide fuel cells are a major impediment to their widespread use in power generation. Thus, reducing this operating temperature is currently a major materials research goal, involving the search for novel electrolytes as well as active catalysts for electrode kinetics (oxygen reduction and hydrogen oxidation). Among oxide-ion conductors, those of anion-deficient fluorite structures such as yttria-stabilized zirconia (YSZ), xY{sub 2}O{sub 3}:(1-x) ZrO{sub 2}, are extensively used as electrolytes in SOFCs. Doping with Y{sub 2}O{sub 3} is known to stabilize the cubic fluorite structure of ZrO{sub 2} and to supply the oxygen vacancies responsible for the ionic conduction. These materials are characterized by a large number of mobile oxygen vacancies, which are randomly distributed in the structure, and thus give rise to a completely disordered anion (oxygen) sublattice. Traditionally, the main strategy to reduce the operating temperature has been to search for novel electrolyte materials with larger oxide-ion conductivity values. Only recently has the use of artificial nanostructures appeared as a promising new direction for dramatically improved properties.
- Research Organization:
- Oak Ridge National Lab. (ORNL), Oak Ridge, TN (United States)
- Sponsoring Organization:
- USDOE Office of Science (SC)
- DOE Contract Number:
- DE-AC05-00OR22725
- OSTI ID:
- 1022625
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
02 PETROLEUM
08 HYDROGEN
ANIONS
ANODES
CATALYSTS
COMBUSTION
ELECTRODES
ELECTROLYTES
ELECTRONS
ENGINES
FLUORITE
FUEL CELLS
GASOLINE
HYDROGEN
IONIC CONDUCTIVITY
KINETICS
MEMBRANES
NANOSTRUCTURES
OXIDATION
OXIDES
OXYGEN
PHOSPHORIC ACID
POWER GENERATION
SOLID ELECTROLYTES
SOLID OXIDE FUEL CELLS