Spinel structure Co3O4 nanoparticles with an average diameter of around 17nm were prepared and evaluated as electrocatalysts for H2O2 reduction. Results revealed that Co3O4 exhibits considerable activity and good stability for electrocatalytic reduction of H, 02 in 3 M NaOH solution. The reduction occurs mainly via the direct pathway when H2O2 concentration is lower than 0.5M. An Al-H2O2 semi fuel cell using Co3O4 as cathode catalyst was constructed and tested at room temperature. The fuel cell displayed an open circuit voltage of 1.45 V and a peak power density of 190 mW cm(-2) at a current density of 255 mA cm(-2) operating with a catholyte containing 1.5 M H2O2. This study demonstrated that Co3O4 nanoparticles are promising cathode catalysts, in place of precious metals, for fuel cells using H2O2 as oxidant. (c) 2007 Elsevier B.V. All rights reserved.