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The adsorbate-induced surface stress was studied for the system CO/Pt111-textured thin films in CO-saturated 0.1 M HClO4and characterized through the techniques of cyclic voltammetry and chronoamperometry. A compressive stress of −1.1 N/m was measured for a saturation coverage. It is shown that CO blocks the electrode both electrochemically (charge transfer) and physically (surface stress changes). Additionally, it is demonstrated with surface stress measurements that CO does not desorb with the removal of CO from the electrolyte. The adsorption kinetics of CO are shown to be slow, with a saturation coverage taking more than 65 s to acquire. When driven electrochemically, CO oxidation kinetics are fast, occurring in much less than 1 s.

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 Pt111 and Au111 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.

The under-potential deposition (UPD) & absorption of hydrogen in thin film palladium (45–75 nm) was investigated electrochemically utilizing both EQCM and thin film stress measurement techniques. The total frequency change during H absorption (desorption) as measured by EQCM is attributed to both an increase (decrease) in mass, Δfm, as well as the associated thin film stress evolution, Δfs. In order to deconvolute these two contributions,the changes in the Pd{111} thin-film stresses were measured directly by a high-resolution cantilever curvature-based stress monitoring technique. Mass incorporation and stress generation due to hydrogen absorption were recorded during cyclic voltammetric scans of increasingly cathodic potentials as well as during chronoamperometric holds in the hydrogen UPD region. The combination of stress measurements and mass uptake of hydrogen in the purely elastic regime provided a measure of a biaxially constrained partial molar volume of hydrogen in the Pd thin films, V¯H−Pdbiax= 0.44 cm3/mol. Additionally, the occurrence of hysteresis and dramatic changes in slope of stress vs. H concentration during loading and unloading of thin films is explained in the context of elastic-plastic transitions that occur in the film.