THERMOELECTRIC-POWER OF YSZ

Thermoelectric power of an yttria stabilized zirconia (YSZ) thermocell , Pt\YSZ\Pt, has been determined at 1273 K in different atmospheres. T he atmospheres used have been mixtures Of O-2-inert gases, CO-CO2, and H-2-H2O. Oxygen partial pressures ranged between 1 and 10(-21) atm. T he yttria content in the YSZ was 8 mol%. The dependence on temperature of the thermoelectric power of YSZ in air has also been measured betw een 600 and 1100-degrees-C. The thermoelectric power was determined to be 0.486 mV/K in air at 1 atm, the colder end was positive relative t o the hotter end. The transported entropy of O-2- in yttria-stabilized zirconia is calculated from a combination of thermodynamic and measur ement data and is found to be 33 JK-1 mol-1, independent of oxygen par tial pressure and temperature. It is shown that the major contribution to the measured thermoelectric power comes from the entropy change of the electrode reactions. It is possible, from the thermoelectric powe r of a YSZ thermocell, experimentally to determine approximative value s of the single electrode reversible heat evolution in an SOFC. These calculations give that 60 kJ/mol e- will be evolved at the cathode whe n air is the cathode gas and 41 kJ/mol e- will be consumed at the anod e in a mixture of 98% H-2 and 2% H2O, at 1273 K when the total gas pre ssure at both cathode and anode is 1 atm.