Co3O4 spinel type nanoparticles (5-10 nm) were synthesized by oxidizing precipitation in various basic solutions. The materials prepared in lithium-containing hydroxide solutions exhibit high electronic conductivity (higher than 10(-2) S.cm(-1) at room temperature), which can be increased (up to 3 S.cm(-1)) by electrochemical oxidation. This high conductivity is due to the presence of Co4+ ions in the octahedral framework of the spinel structure, which entails electronic delocalization. In addition to high conductivity, the obtained powder exhibits a high surface area (around 200 m(2).g(-1)), which should be suitable for applications in electrodes: as conductive additive in the positive electrode of alkaline Ni-MH cells, or directly as electrode material in hybrid C/metal oxide supercapacitors. (C) 2012 The Electrochemical Society. [DO!: 10.1149/2.036212jes] All rights reserved.