There are few mass transfer studies to nanocatalysts (1 nm ≤ dp ≤ 100 nm). We have experimentally investigated the electrocatalytic reduction of hexacyanoferrate (III) to hexacyanoferrate (II) on gold nanospheres. The surface flux is insensitive to particle sizes of dp≥ 30 nm. For particle sizes of dp < 30 nm, the flux increases sharply with decreasing particle size. However, the measured fluxes are one to three orders of magnitude smaller than predicted by a purely diffusion-limited model. Using mathematical modeling, we evaluated six mechanisms potentially affecting mass transfer to a nanoparticle. Flux concentration due to the curvature effect and electromigration become important below 30 nm. Stabilizing layers on the particle also greatly influence the flux through electrosteric effects. Brownian advection, enhanced surface reactivity, and particle aggregation play negligible roles. Tuning the charge and the tortuosity of the stabilizer layer to potentiate the flux may be useful in nanosuspensions.

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.