The surface force between a silica sphere and a copper electrode was measured in concentrated solutions of MgSO4 with an atomic force microscope as a function of the electrode potential. The interaction between the two surfaces was compared with the DLVO theory, and the surface potential of the copper electrode was determined as a function of the cathodic overpotential. The potential of zero charge of the copper electrode was identified in this way. This was found to correspond to the potential of zero charge obtained from the differential capacitance minimum. Moreover, the influence of the pH on the surface force between silica and copper was examined and the presence of a chemically adsorbed oxygen layer on copper was deduced from force measurements at high pH.