DETERMINATION OF POTENTIAL OF ZERO-CHARGE ON SOLID METALS

An attempt has been made to evaluate several experimental methods by which the potentials of zero charge (pzc) of metals could be concordantly measured. The methods chosen involved measurements of the adsorption in the double layer of a neutral organic compound as a function of the concentration of the supporting electrolyte; double-layer capacitance as a function of potential; and static friction between surfaces in solution. The pzc for Pt containing a negligible amount of H is Eq=0 = 0·56 (±0·07) - 0·067 pH (3 methods). For Au, Eq=0 = 0·15 ± 0·02 (2 methods). For Ag, Eq=0 = -0·44 ± 0·02 (2 methods). For Ni, Eq=0 = -0·26 ± 0·06 (3 methods). Introduction of H into Pt shifts the pzc in the negative direction. Anodic and cathodic pulsing of Au and Ag electrodes produced surfaces which gave pzc values 0·2 and 0·4 V respectively more positive than those for unpulsed electrodes. Results reported earlier for Pt are for Pt containing dissolved H. The dissolved proton concentration, abnormally high near the surface, contributes significantly to the surface potential. The results obtained oil pulsing of silver and gold are for dermasorbed surfaces. The most satisfactory methods for the determination of the pzc are the capacitance, static friction, immersion, and tension vibration methods. © 1969.