Gold electrodeposition in organic media

Organic species are easily adsorbed onto metal electrodes, due to the high surface energy. This principle is widely employed in electrodeposition to obtain grains with a given shape and size. Electrodeposition in organic electrolytes and ionic liquids is expected to produce deposits whose properties will be modified by the nature of the species present in the bath. Here, we analyse the voltammetric profiles for the reduction of two different gold complexes, tetrachloroaurate (III) (AuCl4-) and dicyanoaurate (I) (Au(CN)2-), in dimethylsufoxide (DMSO) and in the ionic liquid tributylmethylammonium bis(trifluoromethylsulfonyl)imide (TBMA+NTf2-). We evaluate how organic cations present in the electrolyte modify not only the voltammetric response but also the morphology of the deposits obtained. The films range from very smooth with a rms roughness of ∼10 nm for 500 nm film to rough globular or facetted films with a crystalline size of ∼200 nm.

► Tetrabutylammonium covers ∼30 % of the total electrode surface area.
► Tetrabutylammonium slows down the electroreduction of AuCl4- to AuCl2-.
► Organic ions influence the shape of grains and roughness of gold electrodeposits.