ADSORPTION OF O-2 AT PT AND KINETICS OF THE OXYGEN REACTION AT A POROUS PT ELECTRODE IN CONTACT WITH A SOLID OXIDE ELECTROLYTE

The oxygen-platinum interaction and polarization resistance (Rη) of ethe oxygen reaction at a porous platinum electrode in contact with solid oxide electrolyte (0.9ZrO2+0.06Sc2O3+0.04Y2O 3) have been studied at temperatures 825-1031 K and P02 1-4.6×10-9 atm. Isotherms of weakly bound oxygen (Δns) on Pt have been obtained. Adsorption isotherms have been calculated assuming 1/Rη to be proportional to θ(1-θ), where θ is the equilibrium surface coverage of platinum by atomic oxygen. θ-P02 and Δns-P02 curves proved to be close. The oxygen adsorption heat at θ≤ (0.35-0.5) has been obtained to be 171∓5 kJ/mol. The activation energy of Rη of the oxygen reaction is 145±5 kJ/mol and independent of θ. The oxygen reaction rate near the equilibrium potential is limited by the diffusion rate of atomic oxygen over the platinum surface to (from) the three-phase line gas-platinum-electrolyte or by the occupation (liberation) rate of the reaction sites along the triple line at distances from the latter not more than 10-7 cm. © 1990.