Scanning electrochemical microscopy (SECM) has been used to study electron transfer at Al and Al alloy surfaces, employing the mediators hydroquinone, hydroquinone sulfonate, anthraquinone-2,6-disulfonate, and anthraquinone-2-sulfonate. Both oxidation and reduction processes are examined. SECM, in combination with scanning electron microscopy/energy-dispersive X-ray analysis, reveals that Cu-containing secondary phase particles exhibit the highest electron transfer activity for both oxidation and reduction reactions on the AA 2024-T3 surface. Although electron transfer is fastest at the intermetallic particles, it also occurs on the alloy matrix under acidic conditions. The charge carried by the mediator appears to have little influence on the electron transfer process despite the fact that the matrix oxide surface is positively charged below pH 7. (c) 2008 The Electrochemical Society.