Reaction kinetics of the Pt, O-2(g)vertical bar c-ZrO2 system: precursor-mediated adsorption

A micro kinetic model of the Pt, O-2(g) was developed in state space form ( model M3). The oxygen adsorption/desorption process was modeled as a precur sor-mediated surface reaction. The surface diffusion of atomic oxygen and t he electrochemical reduction of atomic oxygen near the three-phase boundary (tpb) were considered. It was shown that the simulated charge-transfer beh avior of M3 is significantly different from models with ordinary Langmuir k inetics (model M2). The electrochemical rate constant was estimated from se lected experimental data as k(10) = (6.05+/-0.25).10(6) m(3) /(mol.s). From experimental results it was concluded that only one adsorbed oxygen specie s is relevant for the dynamic behavior. In porous Pt electrodes binary gas phase diffusion of oxygen in O-2/N-2 gas mixtures becomes relevant at oxyge n partial pressures below similar to 10(-3) atm. The general procedure for state and parameter estimation can be well adopted for the investigation of further reaction mechanisms. (C) 1999 Elsevier Science B.V. All rights res erved.