Effect of underpotential deposition of lead on polarization behavior of nickel in acidic perchlorate solutions at room temperature

The effect of Pb2+ on polarization behavior of nickel has been investigated in 0.1 M NaClO4 + 10−2 M HClO4 + x M PbO solutions (x = 0, 10−5, 10−4, 10−3) at room temperature. The cyclic voltammogram has suggested that Pb2+ degrades the stability of the passive film on Ni. The corrosion potential of Ni shifted to the more noble direction and the anodic current peak of Ni dissolution decreased with increasing Pb2+ concentration in solution, indicating that Pb2+ suppresses significantly the anodic dissolution. The underpotential deposition (UPD) of lead on Ni in the potential range more noble than −0.215 V (SHE) corresponding to the equilibrium potential of the Pb2+ (10−3 M)/Pb electrode was confirmed by XPS and GDOES analyses. The anodic Tafel slope, b+, of Ni dissolution changed from b+ = 40 mV decade−1 in the absence of Pb2+ to b+ = 17 mV decade−1 in the presence of 10−4 or 10−3 M Pb2+, which was ascribed to the increase in active sites of Ni surface emerged as a result of electrodesorption of Pb adatoms. The roles of Pb adatoms in active dissolution and active/passive transition of Ni were discussed from the above results.