(257d) Anodic Oxide Growth on Gold Electrodes Measured Using an Electrochemical Surface Forces Apparatus (EC-SFA)

Using an electrochemical Surface Forces Apparatus (EC-SFA), we measured in-situ the anodic oxide growth on a gold electrode, as well as the interaction forces between this electrode (both in the state of a metal and a metal oxide surface) and an apposing smooth surface in an electrolyte solution. The EC-SFA allows for control of surface potential and interfacial electrochemical reactions of a gold electrode surface with simultaneous measurements of distances between apposing surfaces (i.e., gold electrode and mica) and normal interaction forces.

Applying a high positive electrical potential on a metal surface will lead to an oxide growth. Using the EC-SFA we compared the measured thickness of the anodic gold oxide layer and the charge consumed for generating this layer. This comparison allowed for the identification of hydrated Au(OH)_3­ phase as the chemical structure of this gold oxide.

The measurements of the interaction forces reveal the formation of a negatively charged gold oxide surface even at the low experimental pH of 3. It is believed that the effective surface potential is due to the surface chemistry, where hydroxide ions adsorbed to the surface leading to a net negative surface charge.

Reference:

1. Valtiner M, Banquy X, Kristiansen K, Greene GW, and Israelachvili JN, Langmuir, 28 (2012) 13080-13093.