Stress Response to Surface Alloying and Dealloying during Underpotential Deposition of Pb on (111)-Textured Au

The stress response during Pb underpotential deposition on (111)-textured Au has been examined on a cantilever beam electrode in perchloric acid supporting electrolyte. We observe a sweep rate dependence for both the individual voltammetric waves and the stress response that we attribute to kinetically controlled surface alloying [(root 3 x root 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 that is coincident with the last voltammetric wave appears to be caused by the formation and removal of the surface alloy. Long-term potentiostatic pulsing experiments show slow stress changes during both the formation and the stripping steps, but only for the incomplete adlayer, confirming slow alloy and dealloy processes at those coverages. The voltammetry and surface stress after extended polarization at potentials where dealloying occurs show that the stable alloy structure and the hcp adlayer coexist and that the relative amounts of these phases are potential-dependent.