The adsorption of polyethylene glycol (MW 20,000) (PEG(20000)) in the presence of Cl- ions onto a polycrystalline gold electrode was studied using a quartz crystal microbalance, AC voltammetry, and chronocoulometry. This study provided new physical insights into the adsorption behavior of this polymer in the presence of chloride ions on a solid electrode in KClO4. Specifically, three potential-based behaviors were observed: the adsorption of PEG(20000) was observed to form a condensed phase in the potential range from -0.90 to -0.62 V vs. SCE. The obtained Delta G(ads) values allow for a hypothesis that adsorption occurs by means of hydrogen bridges. In the potential range from -0.62 to -0.10 V vs. SCE, the addition of chloride does not lead to an increased adsorption of PEG20000, but rather to a simple superposition of both adsorption processes. The potential range from -0.10 to 0.35 V vs. SCE is dominated by the adsorption of Cl- ions, and a displacement of adsorbed PEG(20000) molecules associated with the adsorption of Cl- anions was observed. Based on the obtained Delta G(ads) values, we propose that, in this potential range, the interaction of the PEG(20000) molecules with the Au polycrystalline electrode surface is defined as weak chemisorption via the oxygen atoms. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.065203jes] All rights reserved.