Dynamic Stress Analysis Applied to (111)-Textured Pt in HClO₄Electrolyte

Abstract

Dynamic stress analysis (DSA) was performed on Pt cantilever electrodes immersed in 0.1 mol/L HClO4 electrolyte. DSA combines elements of electrochemical impedance spectroscopy (EIS) and cantilever curvature. In this paper DSA is used to determine the relationship between surface stress f and charge density q for (111)-textured Pt as a function of steady state potential. The parameter of merit is the stress-charge coefficient, ξ, a complex number, which is obtained from the product of the electrochemical impedance Ze and the stress admittance Ys. The magnitude and sign of ξr, the real component of ξ, quantifies how the surface responds to changes in charge density. Three regions of stress-charge behavior have been identified at potentials bound by hydrogen adsorption and platinum oxide formation. In the hydrogen adsorption region, stress and charge are in phase, resulting in a positive value of ξr. In the double layer region the surface stress and the charge density are 180° out of phase, yielding a negative value of ξr. The actual potential at which this phase angle transition occurs may vary by as much as 0.3 V, depending on electrode history. At more positive potential ξr remains negative in the early oxide region, where the reversible adsorption of O occurs. Only at more positive potential, where place exchange between Pt and O occurs and the surface layer of PtO becomes fully formed, does ξr transition back to a positive value. The experimental methods described in this work provide a means to probe the dynamic behavior of surface stress.