Potential dependent surface relaxation of the Pt(001)/electrolyte interface

X-ray reflectivity measurements were used to determine the structure of the Pt (001) /solution interface as a function of the applied potential in alkaline and acid electrolytes. Unlike the Pt (001) /vacuum interface, the electrolyte interface was found to be unreconstructed at all potentials. The lattice spacing between the first and second layer was found to be a funciton of potential in the region where approximately a monolayer of H was adsorbed. The expansion was up to 2. 5% of a lattice spacing (0. 05) in alkaline electrolyte, and up to 1% of a lattice spacing in acid electrolytes.