Kinetics of monolayer Bi electrodeposition on Au(111): Surface X-ray scattering and current transients

The kinetics of Bi monolayer electrodeposition (underpotential deposition) on the Au(111) electrode was investigated using surface X-ray scattering and electrochemical methods. The current and X-ray intensity transients were measured simultaneously using a low-resistance drop cell that has a potential response time less than 50 mus. Three independent measurements of the Bi coverage transients were obtained, which are related to (1) the integrated charge, (2) the adsorbed Bi, irrespective of the adsorption site, and (3) the adsorbed Bi with a well-defined (2x2) structure. The zero-coverage <----> commensurate (2x2)-Bi phase transition occurs on the millisecond time scale, 3 orders of magnitude more rapidly than the (2x2)-Bi <----> high-coverage incommensurate (pxroot3)-2Bi phase transition. Nucleation and growth kinetics was observed for both transitions involving Bi desorption. Langmuir adsorption kinetics was observed for both transitions involving Bi adsorption. Comparison of the total coverage with that measured by in-plane diffraction intensity suggests fast coarsening of islands for the transition for the zero-coverage <----> commensurate (2x2)-Bi phase transition.