Chemical surface exchange of oxygen on CeO_(2−δ) in an O_2/H_2O atmosphere

Abstract

The chemical surface reaction rate constant controlling the change of oxidation state of undoped ceria, k_(Chem), was measured at 1400 °C in the range of (∼0 ≤ (pH_2O/atm) ≤ 0.163(9)) and (10^(−3.85) ≤ (pO_2/atm) ≤ 10^(−2.86)) via the electrical conductivity relaxation method. In humidified atmospheres, k_(Chem) is fully described as the sum of k_(Chem,O2) and k_(Chem,H2)O, which are, respectively, the rate constants for oxidation by O_2 and by H_2O alone. Using measurements under appropriately controlled gas conditions, the total rate constant is found to follow the correlation k_(Chem)/cm s^(−1) = 10^(−(1.35±0.07)) × (pO_2/atm)^(0.72±0.02) + 10^(−(3.85±0.03)) × (pH_2O/atm)^(0.36±0.03) where the pO_2 and pH_2O values of relevance are explicitly those of the final gas condition. The results suggest that at such high temperatures, the concentrations of surface adsorbed species are too low to influence the independent reaction pathways.

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