Comparative study of electrodeposited copper nanoparticles on different substrates for their use in the reduction of nitrate ions

Abstract

A comparative analysis of the electrodeposition of copper nanoparticles (CuNPs) was studied on highly oriented pyrolytic graphite (HOPG) and vitreous carbon (VC) substrates from solutions containing different supporting electrolytes (Na2SO4 and H2SO4).Voltammetric results indicated the presence of a single cathodic process, corresponding to the reduction reaction of Cu2+ ions to Cuo, for the solutions studied, using the HOPG substrate. The solution containing Na2SO4 as supporting electrolyte was found to be more effective because the copper reduction process occurs at more positive potential values, reaching the highest current density. For the VC substrate, two cathodic processes were evidenced, with the formation of Cu+ ions as intermediate species. As in the HOPG substrate, the use of the solution containing Na2SO4 showed the better behavior for copper electrodeposition, being the most favored process on VC. This behavior could be explained by considering the existence of structural defects in the VC, which would facilitate Cu nucleation.The nucleation and growth kinetics of CuNPs on HOPG electrodes corresponded predominantly to a model including progressive nucleation on active sites, and diffusion controlled growth, presenting a good correlation with the scanning electron microscopy images. For VC substrates, the kinetics analysis did not yield conclusive results. Different morphological features of Cu deposits were observed on HOPG and VC, presenting the former a larger covered area.The HOPG/CuNPs modified electrodes evidenced an enhancement in the catalytic activity towards the nitrate reduction reaction.