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 m ol/dm(3) solutions at 0 degreesC by voltammetric and FTIR spcetroscopic tec hniques. Voltammetric redox waves of specific adsorption of sulfate and pho sphate anions at pH 3 on the Cu(100) electrode are separated from hydrogen evolution reaction (her) and is clearly shown by the charge displacement ad sorption of CO. Perchlorate anion is not specifically adsorbed on the Cu(10 0) electrode, and no redox wave is observed. Specific adsorption of phospha te 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-desor ption 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 adso rbed phosphate species on the Cu(100) electrode in the Cu(100) pH range stu died. Most of the negative charge of the phosphate anions is withdrawn by t he electrode, bringing the pK(a) value of the anions significantly down in the specific adsorption process. (C) 2001 Elsevier Science Ltd. All rights reserved.