Effect of sulfuric acid concentration on the structure of sulfate adlayer on Au(111) electrode

The adsorption of sulfate on A(111) single-crystal electrode was examined in sulfuric acid solutions of various concentrations (0.5-7.5 M) by cyclic voltammetry and in situ scanning tunneling microscopy (STM). The well-known sulfate adlayer with (root 3 x root 7) unit cell was found in 0.5 M sulfuric acid by in situ STM. In 2.5 and 5.0 M sulfuric acid, a new order-disorder phase transition, from the (root 3 x root 7) adlayer to a disordered structure, was found to take place at ca. 1.1 V vs. Ag vertical bar AgCl vertical bar KCl(sat.). In 7.5 M sulfuric acid, no current spikes were seen in the CV profile, and in situ STM showed that the sulfate adlayer was disordered. (c) 2006 Elsevier B.V. All rights reserved.