Influence of Composite Additive on Gold Electrodeposition in DMH-Based Electrolyte: Combined Experimental and Theoretical Study

Abstract

The comparison of macroscopic appearance and microscopic morphology of gold electrodeposit determined PHEN as the main brightener for its effective influence on refining the grains, resulting in a golden bright and shiny deposit. Improving the flatness of deposit when used together with PHEN, PDDA was the auxiliary brightener, thereby obtaining thicker deposits. Results of TEM and XRD showed that the average size of refined gold crystals was about 20 nm. We speculated from the patterns of XPS that the action of the additive molecule is to adsorb on the metal surface. Combined electrochemical measurements and MD simulations revealed that both PHEN and PDDA molecules could steadily adsorb on the surface of Ni and Au, increasing the polarization of the cathode surface and promote the refinement of grains. PHEN was the main additive when used as a composite additive for its higher adsorption energy than PDDA. The effective adsorption of PHEN and PDDA molecules led to the enhancement of cathodic polarization, causing the negative shift of potential and the decrease of current in cyclic voltammetry of the second step reduction. The chronoamperometry measurements indicated that the nucleation process was a progressive model. The grain growth was significantly inhibited when the additives were used.