Sulphate electrosorption on liquid gallium from water

The electrosorption of sulphate ions on liquid gallium from aqueous solutions of Na2SO4 + H2SO4 with concentrations ranging from 0.01 to 0.63 M was investigated on the basis of capacitive charge measurements carried out by a computerized chronocoulometric technique and of differential capacity measurements. The unit slope of the Parsons-Zobel plot at zero charge and the concentration independence of the difference E - ø2 between the applied potential E and the Gouy-Chapman potential ø2 at the outer Helmholtz plane confirm the validity of the Gouy-Chapman-Grahame theory. The potential of zero charge Ez is independent of the electrolyte concentration and is equal to -960±5 mV vs. a molar calomel electrode (MCE). A qualitative justification is provided for the difference between this Ez value and the potential of zero charge, Ez = -920 ±5 mV/MCE, at the interface between liquid gallium and aqueous solutions of the non-specifically adsorbed NaClO4 salt.