Surface Properties of Nanostructured Gold Coatings Electrodeposited at Different Potentials

Nanostructured gold coating were synthesized on the surface of screen-printed carbon electrode (SPCE) via electrodeposition technique from acidic gold solution at four different potentials (i.e.: +1.0 V, +0.48 V, -0.3 V and -0.7 V). The gold coatings were characterized by FESEM, EDAX and XRD for their morphology, elemental composition and crystallite size, respectively. The electrochemical active surface area (ECSA) and electron transfer of gold nanostructures were investigated by cyclic voltammetry (CV) analysis in 0.5 M H2SO4 and in 1 mM Fe (CN)6-3/-4 + 0.1 M KCl solution, respectively. Deposition at +1.0 V has produced gold coatings with tetrahedral like structures as imaged by FESEM. Meanwhile, deposition at +0.48 V, a coating formed was quasi-spherical and facetted crystalline structures. However, deposition at more cathodic potential (i.e.: -0.3 V) resulted in the formation of dendrite-like gold nanoclusters with several micrometres of stem structures. Large micrometres of stem and feather-like branches were formed for deposition at more negative potential of -0.7 V. The EDAX analysis showed that the nanostructured gold coating deposited at +0.48 V has the highest gold purities with elemental composition of 99.68 wt. %. The XRD analysis revealed that all nanostructured gold coatings were composed of cubic crystallite structures where the highest crystallite size of 93.18 nm was obtained for deposition at -0.7 V. Furthermore, the coating deposited at -0.7 V also has the highest ECSA value of 3.851 cm2 as well as the highest oxidation and reduction current peak for Fe (CN)6-3/-4 reaction which demonstrated the best electron transfer by CV. The electrochemical kinetic mechanism on its surface is predominantly controlled by a linear diffusion.