Pt{111} and Au{111} Electrocapillarity:  Interphase Structure, the pzc, and Oxygen Reduction

Large changes in stress (of order GPa) are observed with relatively modest variations in applied potential (on the order of 500 mV), even in nonspecifically adsorbing electrolyte solutions. Here we present the electrocapillarity behavior (in situ surface stress evolution) of Pt{111} and Au{111} electrodes. We relate the magnitude and anodic/cathodic hysteresis of the stress−potential behavior to the potential dependent water orientation at the electrode/electrolyte interface. We show that our results are strongly correlated to previously published infrared spectroscopy data on the potential dependence of interphase structure. Finally, measurements of Pt in oxygen saturated electrolytes are presented, allowing for a direct comparison between features in the surface stress behavior and the “turn-on” potential for oxygen reduction. We found that oxygen reduction occurs only once the potential was cathodic enough to begin depleting the interface of oxygen-down oriented water.