Electrocapillary coupling during electrosorption.

The electrocapillary coupling coefficient, ς, measures the response of the electrode potential, E, to tangential elastic strain at the surface of an electrode. Using dynamic electro-chemo-mechanical analysis, we study ς(E) simultaneously with cyclic voltammetry. The study covers extended potential intervals on Au, Pt, and Pd, including the electrosorption of oxygen species and of hydrogen. The magnitude and sign of ς vary during the scans, and quite generally the graphs of ς(E) emphasize details which are less obvious or missing in the cyclic voltammograms (CVs). Capacitive processes on the clean electrode surfaces exhibit ς < 0, whereas capacitive processes on oxygen-covered surfaces are characterized by ς < 0 on Au but ς > 0 on Pt and Pd. The findings of ς < 0 during the initial stages of oxygen species adsorption and ς > 0 for hydrogen electrosorption agree with the trend that tensile strain makes surfaces more binding for adsorbates. However, the large hysteresis of oxygen electrosorption on all electrodes raises the question: is the exchange current associated with that process sufficient for its measurement by potential response during small cyclic strain?