Particle size dependence of the electrocatalytic activity of nanocrystalline RuO2 electrodes

The effect of nanocrystal size/shape on the electrocatalytic behavior of nanocrystalline oxide electrodes was demonstrated on electrodes based on sol-gel-prepared RuO2 materials. The typical particle size ranged between 15 and 40 nm. Regardless of the particle size, the nanocrystals were of isometric shape with polygonal prismatic part capped with two pyramids. The prismatic part of the nanocrystals featured {110}- and {100}-oriented faces in the case of small nanocrystals (d < 20 nm) and {110}, {100} and {140} in the case of bigger nanocrystals (d > 20 nm). The pyramidal parts were formed by {101}-oriented faces. The activity of the RuO2 nanocrystals towards oxygen evolution reaction decreases with increasing particle size; the activity towards chlorine evolution is insensitive to the particle size/shape. The observed tendency indicates that the oxygen evolution is significantly affected by the crystal edges while chlorine evolution reaction proceeds mainly on crystal faces. The suppression of the oxygen evolution may be connected with the absence of edges separating the {110}-{100} faces on the prismatic part of the bigger nanocrystals. The {110}-{100} edges can be therefore regarded as the preferential site for O-2 evolution. (C) 2006 The Electrochemical Society.