Catalytic formation of nanochannels in the surface layers of both pure diamond crystallites and conductive boron-doped diamond (BDD) electrodes was performed using a few metal nanoparticles (Co, Nb, Mo, and W) in a hydrogen atmosphere. Thermogravimetry in the hydrogen atmosphere showed the beginning of the consumption of diamond at temperatures higher than ca. 700 degrees C. The nanochannels grew parallel to the crystallite edges, and had a characteristic morphology consisting of flat walls perpendicular to the flat base. The extent of the channeling behavior did not depend on the content of the boron in the BDD. Cyclic voltammetry showed that the surface area of the BDD was increased several times over by the formation of the nanochannels and holes. This simple method to increase the surface area of diamond materials is useful for introducing several new functionalities, including the production of high-current-density BDD electrodes, and of loading-sites for fine catalyst metals or compounds, etc. (c) 2006 The Electrochemical Society.