Abstract
Absolute values of changes in surface energy of gold electrode in perchlorate solutions with and without iodide ions were measured by a laser‐beam deflection method. The potential of the electrocapillary maximum or potential of zero charge (pzc) obtained by the laser‐beam deflection method was in good agreement with that obtained previously by a piezoelectric technique. The derivative of surface energy with electrode potential, 
, was quite different from the surface charge density, 
, obtained with integration of current density in the cyclic voltammogram, indicating that the simple Lippmann equation, that is, 
, did not hold. Particularly, 
took a maximum near the potential at which the charge transfer of adsorbed iodide ions occurred to form the iodine adlayer despite the fact that 
increased monotonically with increasing potential. The above results obtained by the laser‐beam deflection method were also consistent with those obtained previously by the piezoelectric technique. The discrepancy between 
and 
was ascribed to the changes in surface elastic strain accompanied by the structural changes of the adlayer. © 1999 The Electrochemical Society. All rights reserved.