Abstract: The AC impedance properties of the air electrodes using multi-walled carbon nanotubes, active carbon and graphite particles as catalyst layer material were investigated. The results showed that the AC impedance diagram of carbon nanotubes consisted of two semi-circles, in which the high frequency zone was ascribed to the ohmic process within porous structure and the low frequency zone to the kinetic impedance of electrochemical reaction. The Pt nanoparticles deposited on the exterior surface of carbon nanotubes decreased greatly ohmic and electrochemical impedance, so increased electro-catalytic activity of oxygen reduction. However, for the air electrode prepared by active carbon, the thin film diffusion impedance was appreciably observed in addition to ohmic impedance. The low catalytic activity in the graphite air electrode appeared as a consequence of the decreased thin film reaction sites and the mass transport process was dominated by Warburg diffusion. Finally, the equivalent circuit of air electrode was proposed and the simulated kinetic data were also discussed.

Key words: Carbon nanotubes, Air electrode, AC impedance, Oxygen reduction