Suppressing Sulfite Dimerization at a Polarized Gold Electrode/Water Solution Interface for High-Quality Gold Electrodeposition.

Solid/liquid interfacial structure occupies great importance in chemistry, biology, and materials. In this paper, by combining EC-SERS study and DFT calculation, we reveal the adsorption and dimerization of sulfite (SO) at a gold electrode/water solution interface, and establish an adsorption displacement strategy to suppress the dimerization of sulfite. At the gold electrode/sodium sulfite solution interface, at least two layers of SO anions are adsorbed on the electrode surface. As the applied potential shifts negatively, the adsorption strength of the first SO layer is weakened gradually and then is dimerized with the second orientated SO layer to form SO, and SO is further reduced to SO. After hydroxyethylene disphosphonic acid (HEDP) is introduced to the gold electrode/sodium sulfite solution interface, the second oriented SO layer is replaced by a HEDP coadsorption layer. This results in the first layer of SO being desorbed directly without any structural transformation or chemical reaction as the potential shifts negatively. The suppression of sulfite dimerization by HEDP is more clear at the gold electrode/gold sulfite solution interface owing to the electroreduction of gold ions. Furthermore, the electrochemical studies and electrodeposition experiments show that as the sulfite dimerization reaction is suppressed, the electroreduction of gold ions is accelerated, and the deposited gold coating is bright and dense with finer grains.