In principle, metal particles can be electrodeposited on electrode surfaces under conditions where individual metal particles grow independently of neighboring particles on the electrode surface, and the growth rate for every particle on the surface is the same. In this "uncoupled limit", extremely narrow particle size distributions will be attainable. We describe the conditions of nucleation density, electrodeposition duration and rate for which this uncoupled growth regime can be obtained. When these growth conditions are implemented to grow silver and gold meso-scale particles on graphite electrode surfaces, narrow (RSD_dia < 10%) particle size distributions are obtained for particles with mean diameters in the range from 50 nm to 2.0 microns.

Figure 1. Spatial relationship of depletion layers for the uncoupled and coupled electrodeposition of particles on an electrode surface.

Figure 2. Particle size histograms and scanning electron micrographs for the Slow-grow silver particle dispersions on HOPG. analyzed at right. All particles shown here were electrodeposited using an overpotential of -70 mV. The deposition duration was: a. 500 ms., b. 1.0 s., c. 5.0 s., d. 10 s., e. 30 s., f. 120 s.

Figure 3. Plot of the slope of the correlation plot versus R, the correlation coefficient, for experiments conducted at Ð70 mV vs. Ag+/Ago (RED), and at Ð500 mV (BLUE). The error bars represent + 1 standard deviation of the slope values from the regression line.

For normal, "fast growth" experiments carried out at -500 mV, a clear correlation exists between the distance between neighboring particles and the mean size of two nearest neighbors. This "finger print" of interparticle diffusional coupling is not seen for silver particle dispersions prepared at -70 mV. This result provides support for the hypothesis that interparticle diffusional coupling provides the primary mechanism by which size dispersion develops in metal particles prepared by electrodeposition.