Oxygen exchange on platinum in zirconia electrochemical cells

Thesis/Dissertation · Fri Jan 01 04:00:00 EST 1988

OSTI ID:6849437

Robertson, N L

Electrochemical cells based on high-temperature solid oxide ionic conductors such as yttria-stabilized zirconia are popular as oxygen sensors and are under increasing study for use as fuel cells. A better understanding of the kinetics of the most fundamental reaction at the electrodes in these cells, oxygen exchange between the gas and electrolyte, is needed to better utilize these electrochemical cells. Oxygen exchange kinetics on porous platinum electrodes in a zirconia electrochemical cell were measured at 600-800 C in 10{sup {minus}5} to 0.21 atm oxygen. Steady-state polarization and potential-step chronoamperometric experiments were performed. Steady-state current-voltage characteristics exhibited limited Tafel regions and anodic and cathodic limiting currents. At and below 600 C, the initial decay of the current following anodic and cathodic potential steps was linear in 1/(time){sup {1/2}}. This Cottrell-type behavior indicates that the charge-transfer step in the mechanism of oxygen exchange must occur at the three-phase boundary where the electrode, electrolyte, and gas-phase intersect and not in the two-phase electrode-electrolyte interface as has been previously suggested. The potential-step experiments were also used to study the capacitance of the double layer at the interface between the electrode and the electrolyte. The capacitance is independent of oxygen partial pressure and electrode potential and increases from 0.2 {mu}F/cm{sup 2} at 555 C to 1.3 {mu}F/cm{sup 2} at 695 C. These values are at least ten times smaller than the capacitances measured by AC methods indicating that the capacitive behavior of the electrodes in zirconia cells is dominated by time-dependent faradic processes.

• Research Organization: California Univ., Berkeley, CA (USA)
• OSTI ID: 6849437
• Country of Publication: United States
• Language: English

Related Subjects

30 DIRECT ENERGY CONVERSION
300505* -- Fuel Cells-- Electrochemistry
Mass Transfer & Thermodynamics
CAPACITANCE
CHALCOGENIDES
CHEMICAL REACTION KINETICS
DIRECT ENERGY CONVERTERS
ELECTRICAL PROPERTIES
ELECTROCHEMICAL CELLS
ELECTRODES
ELEMENTS
FUEL CELLS
KINETICS
MASS TRANSFER
METALS
NONMETALS
OXIDES
OXYGEN
OXYGEN COMPOUNDS
PHYSICAL PROPERTIES
PLATINUM
PLATINUM METALS
PRESSURE DEPENDENCE
REACTION KINETICS
SOLID ELECTROLYTE FUEL CELLS
TEMPERATURE DEPENDENCE
TRANSITION ELEMENT COMPOUNDS
TRANSITION ELEMENTS
YTTRIUM COMPOUNDS
YTTRIUM OXIDES
ZIRCONIUM COMPOUNDS
ZIRCONIUM OXIDES