This work presents an electrochemical investigation of chemical reactions kinetics in chemical-mechanical polishing of Ta in a peroxide-based alkaline medium. Time resolved Fourier transform electrochemical impedance spectroscopy is combined with cyclic voltammetry to probe the chemical roles of H2O2 and OH- in chemical-mechanical. polishing. Competitive effects of electro-oxidation and oxide dissolution at a Ta disc electrode are studied in four different (nearly neutral, alkaline, peroxide-free and peroxide-containing) electrolytes. In alkaline peroxide solutions with pH greater than or equal to 10, surface catalyzed breakdown of interfacial H2O2 promotes certain reactions of oxide-removal from the Ta surface. These reactions are analyzed in detail. The results demonstrate how the detailed chemical aspects of the process, and kinetics of surface reactions in particular, can be probed in real time by using the method mentioned above. (C) 2004 Elsevier B.V. All rights reserved.