The oxygen reduction reaction (ORR) was experimentally investigated using the Koutecky- Levich approach on AA2024-T3, high-purity aluminum, and high- purity copper. The ORR on a heterogeneous AA2024-T3 electrode exhibited charge- transfer, mixed, and mass-transfer-controlled regimes that were successfully modeled in each regime by considering AA2024-T3 to behave as a regular array of Cu-rich favored cathodic sites in a benign Al matrix. The copper coverage was systematically varied and quantified in both experiments and modeling. The charge-transfer-controlled ORR reaction rate increased linearly with copper coverage, while the mass-transfer-controlled ORR rate increased as a complex function of Cu coverage and the inverse of the boundary layer thickness. Ramifications toward corrosion and its inhibition on AA2024-T3 in thick as well as thin electrolyte layers are discussed. (c) 2005 The Electrochemical Society. [DOI: 10.1149/ 1.1949047] All rights reserved.