The stress during Pb underpotential deposition (upd) on (111)-textured Au has been examined on a cantilever beam electrode in perchloric acid supporting electrolyte. The upd peaks change from double to single going from higher to lower sweep rates, while a sudden stress relaxation (thereafter referred as "the stress hump") becomes more pronounced. We attribute the sweep rate dependence of upd peaks and stress response to kinetically controlled surface alloying [( 3x 3) R30 degrees], which occurs only at low coverage. At high coverage, a hexagonal close packed (hcp) Pb monolayer is formed while the surface alloy is removed. The stress hump appears to be caused by the formation or removal of the surface alloy. Long term potentiostatic pulsing experiments how slow stress changes during both the formation and stripping steps, but only for the incomplete adlayer, confirming slow alloy and de-alloy processes at those coverages. The voltammetry and surface stress after extended polarization at potentials where de-alloying occurs show that the stable alloy structure and the hcp adlayer coexist, and that the relative amounts of these phases are potential dependent.
Citation: Journal of Physical Chemistry C
Pub Type: Journals