ELECTROSORPTION OF IODIDE ON PLATINUM - PACKING DENSITY AND POTENTIAL-DEPENDENT DISTRIBUTIONAL CHANGES OBSERVED INSITU WITH X-RAY STANDING WAVES

We describe the X-ray standing wave technique for directly measuring, in situ, the ionic concentration profile at an electrode/electrolyte interface on the angstrom scale. An X-ray standing wave is generated whenever coherently related incident and reflected X-ray plane waves interfere. In this study, we use X-ray standing waves generated during Bragg reflection from a platinum/carbon layered synthetic microstructure to investigate the electrosorption of iodide on platinum. In the presence of 10 μM sodium iodide in solution, the electrosorption isotherm for iodide showed similarities to that for the Pt(111)/I- system reported previously. In addition, potential-dependent distributional changes (normal to the electrode/electrolyte interface) of iodide in the diffuse layer were inferred from the observed potential-dependent changes in the fluorescence-detected X-ray standing waves. We attempt to relate features in the aforementioned isotherm to the observed distributional rearrangements in the diffuse layer. © 1990 American Chemical Society.