RELATING THE IN-SITU, EX-SITU, AND NON-SITU ENVIRONMENTS IN SURFACE ELECTROCHEMISTRY

The relationship between ultrahigh vacuum surface science and electroc hemistry is examined by comparison of so-called non-situ and ex-situ e xperiments performed in the vacuum environment with in-situ electroche mical experiments. Preadsorbed ClO4, on Ag(110) may be hydrated by pos t-adsorbed water and lifted off the surface as a hydrated complex at 1 70 K. This result directly illustrates the electrochemical concepts of anion desorption and nonspecific adsorption and can be explained by a nalogy to electrochemistry. For ex-situ studies three models exist to describe the key step of removing the electrode from the electrolyte ( emersion): ideal, superequivalent, and dynamic. Ideal emersion obtains upon satisfying the criteria of (1) a 1:1 relationship of emersed wor k function with emersion potential and (2) zero charge transfer upon e mersion. These criteria can be tested by Kelvin probe measurements of the work function in vacuum and re-immersion charge transient measurem ents in the electrochemical cell, respectively. Emersion of Pt(111) fr om 0.1M HClO4, + 1mM Cu2+ exhibits ideal emersion at potentials greate r than 0.7V(RHE) and superequivalent emersion, so called because super equivalent adsorption of ClO4-, and Cl- establishes a constant work fu nction, at emersion potentials less than 0.6V(RHE). The Pb/Pt(111) sys tem exhibits dynamic emersion behavior, characterized by a surface red ox reaction between Pb-0 and Pb2+ that discharges the double layer aft er emersion. Theoretical relationships among the non-situ, ex-situ, an d in-situ methodologies are also briefly reviewed.