Mass Transfer to a Nanocatalyst-Dependence Upon Particle Size

There is presently a paucity of mass transfer studies to single nanocatalyst particles with diameters ranging from 1 nm to 100 nm. We have experimentally investigated the flux associated with the electrocatalytic reduction of hexacyanoferrate (III) to hexacyanoferrate (II) on gold nanospheres. We have found that the flux of hexacyanoferrate (III) to the surface is insensitive to particle sizes in the range of 30 nm ≤ dp ≤ 100 nm. For particle sizes of 5 nm ≤ dp ≤ 30 nm, we see the flux increase sharply as the particle size decreases. While qualitatively the same, the measured fluxes are one to three orders of magnitude smaller than that predicted by a diffusion-limited model. Factors in addition to diffusion are evaluated and discussed, including enhanced surface reactivity of nanoparticles, flux concentration due to sphericity, interactions among particles, presence of stabilizing layers on the particle, and advection due to Brownian motion.