Specific adsorption of phosphate species on Ag (111) and Ag (100) electrodes and their effect at low overpotentials of the hydrogen evolution reaction

Abstract

The influence of the geometry of the silver crystalline faces (111) and (100) on the adsorption/desorption processes of phosphate species as a function of potential is studied, and the surface coverages (θ) and the relaxation times (τ) are compared. A reversible process was observed for Ag(hkl)/KH2PO4 systems from j−V profiles, where a value of 0.07 ML was obtained. For Ag(111)/H3PO4, a coverage of about 0.024 ML was calculated from anodic/cathodic j−V profiles. In the case of Ag(hkl)/K3PO4 systems, highly irreversible processes were observed, resulting in different charge values from integration of anodic/cathodic peaks. For these systems, the capacitance (C(ϕ)) plots are well differentiated for the two faces, and co-adsorption of OH− was evaluated from resistance parameters. Characteristic face-specific relaxation times are obtained for each electrode by Electrochemical Impedance Spectroscopy (EIS). In addition, it was found that the onset potential of her for Ag(111) at pH=1.6 was about 100 mV more negative compared to Ag(100).