Small Pd(0) nanoclusters were observed on the AFM images (Fig.  2 a) with a linear arrangement on the HOPG surface, demonstrating de predisposition of the metal nanoparticles to preferentially attach to defects on the HOPG surface, such as step edges and lattice point defects.

The small nanoparticles deposited on the HOPG step edges (Fig.  2 b) had sizes of 12 to 26 nm height and 50 to 80 nm full width measured at half maximum height (FWHM). .

After 15 CVs, two different adsorbed structures were clearly observed using high-resolution AFM images (Fig.  2 c and d).

Palladium nanoparticles were deposited at the HOPG step edges, as well as randomly nucleated on the HOPG plane terraces, presenting dimensions of 17–50 nm in height and 100–130 nm FWHM (Fig.  2 e)..

In addition to the Pd(0) nanoclusters, very small fragments were observed in the images of 1–5 nm in height (Fig.  2 d and f).

After oxidation of Pd ²⁺ , a layer of palladium metal nanoparticles was formed on the electrode surface and clearly shown by AFM (Figs.  2 and 3 )..

AFM confirmed that Pd(0) nanoparticles were formed during the CVs performed at negative potentials (Fig.  2 a and b)..

Scanning the potential in the positive direction (Fig.  2 c and d), until E  = +0.90 V, two different size adsorbed structures were observed in the AFM images related with the adsorption of large Pd(0) nanoparticles and uniformly distributed smaller palladium oxide nanoparticles on the HOPG surface.

This explains the more uniform distribution of the nanoparticles over the electrode surface formed at E  = +0.90 V when compared with the Pd(0) nanoparticles and nanowires grown at E  = −1.00 V that are preferentially deposited on the HOPG step edges (Figs.  2 a,b and 3 )..

Furthermore, in higher resolution AFM images, scanning the surface for the first time between −0.5 and 0.0 V (Fig.  2 a and b), very small deposits of palladium on the basal plane of the HOPG can be observed, which are easily removed by the AFM tip while scanning the sample.