Single frequency electrochemical impedance investigation of zero charge potential for different surface states of Cu–Ni alloys

Adsorption of sulphate anions onto polycrystalline pure copper, pure nickel and two copper–nickel alloys was explored by performing zero charge potential E _PZC measurements. E _PZC measurements were performed by differential capacitance analysis using single?frequency electrochemical impedance spectroscopy. E _PZC and surface charge of the studied materials were analysed for different surface states: bare—immediately after cathodic polarisation and after 5 h of immersion in a 0.1 M Na₂SO₄ solution. According to the surface state and nature of the studied materials, the choice of the appropriate measuring frequency was investigated. Specific methodologies dedicated to the study of electrode/electrolyte interfaces are then presented for bare metal, metals covered by corrosion products and metals covered by passive film. In the presence of passive film, the space charge capacitance interferes with the differential capacitance measurements, and its influence is discussed in the framework of semiconductor electrochemistry.