Perchlorate adsorption on Au(111) was investigated by cyclic voltammetry and surface-enhanced infrared absorption spectroscopy. We found that the electrosorption valency of ClO4 on Au(111) is similar to 0.6 and the total coverage of ClO4 on Au(111) is higher (similar to 0.15) than previously estimated (similar to 0.04). Based on the experimental adsorption isotherms obtained from infrared spectra and the reconstructionfree cyclic voltammograms, we proposed a mechanism for the CIO4 adsorption on Au(111). (C) 2014 Elsevier Ltd. All rights reserved.