Specific adsorption of anions on a copper (100) single crystal electrode studied by charge displacement by CO adsorption and infrared spectroscopy

Specific adsorption of anions on a Cu(100) electrode was studied with 0.2 mol/dm(3) solutions at 0 degreesC by voltammetric and FTIR spcetroscopic techniques. Voltammetric redox waves of specific adsorption of sulfate and phosphate anions at pH 3 on the Cu(100) electrode are separated from hydrogen evolution reaction (her) and is clearly shown by the charge displacement adsorption of CO. Perchlorate anion is not specifically adsorbed on the Cu(100) electrode, and no redox wave is observed. Specific adsorption of phosphate anions on the Cu(100) was studied in more detail in pH ranging from 1.5 to 12.9. The redox potential of the charge displacement CO adsorption-desorption depends on pH with the slope of ca. 30 mV/pH. Under the assumption of electrochemical equilibrium, PO43- and/or HPO42- are concluded as the adsorbed phosphate species on the Cu(100) electrode in the Cu(100) pH range studied. Most of the negative charge of the phosphate anions is withdrawn by the electrode, bringing the pK(a) value of the anions significantly down in the specific adsorption process. (C) 2001 Elsevier Science Ltd. All rights reserved.