Potentials of zero charge, interaction of metals with water and adsorption of organic substances—I. Potentials of zero charge and hydrophilicity of metals

The most reliable values of the potentials1 of zero charge for metals not adsorbing hydrogen are obtained from the position of the minimum on the differential capacity-potential curves. These data are confirmed by the scrape method and by electron photoemission measurements. However, as it was first found from the comparison of the behaviour of gallium and mercury, at the same potentials referred to pz the adsorption behaviour of various electrodes with respect to the simplest aliphatic surfactants—aliphatic alcohols—differs. This was explained by preferential water chemisorption at electrodes of the gallium type. The determination of the position of the differential capacity curve of the amyl alcohol desorption peak relative to pzc gives a semi-quantitative estimate of the hydrophilicity of various metals, inreasing in the sequence Hg < Bi < Sn < Pb < Cd < In < Ga. The potential at which the differential capacity of the dense layer starts to increase with decreasing negative charge shifts to more negative values relative to pzc in a similar sequence. The obtained results are compared with Trasatti's data. The case of antimony requires further investigation.