Reversible Charging of the Ice–Water Interface: I. Measurement of the Surface Potential

An ice electrode was constructed in order to measure dependency of the surface potential on pH. The electrode had a Plexiglas body with a platinum plate on the bottom, which was cooled by passing the cooling liquid through a tube mounted inside the electrode. The temperature inside the electrode was −7°C, while the electrolyte solution was kept at 0.02°C, so that an ice layer was formed on the platinum plate. In the acidic region fast equilibration of electrode was observed. The slope dφ0/dpH was found to be between −40 and −46 mV. The maximum of the slope was observed at pH 4.4, which coincides with the isoelectric point of ice–water interface. In the basic region the equilibration was slow and more pronounced deviation from the Nernstian behavior was observed. The results were explained on the basis of the surface complexation model, assuming an amphotheric nature of surface OH groups. In the basic region the surface bears high negative charge so that binding of sodium ions at the interface influenced the results.