By a combination of surface sensitive photoelectron spectroscopy and molecular dynamics
simulations we characterize the surface propensity of the iodide anion in aqueous solutions at
acidic, neutral and basic conditions (pH = 1, 6.8 and 13). In both experiments and simulations
an increased surface concentration of I-. in found in non-neutral solutions. We interpret these
findings in terms of I- surface co-adsorption with hydronium at low pH and "salting out" of
iodide by hydroxide from the bulk solution to the surface at high pH. The present study is thus
in accord with the picture of a weak surface adsorption of hydronium and surface depletion of
hydroxide, being in sharp contradiction with the interpretation of electrophoretic and titration
measurements in terms of strong surface enrichment of OH-.