Formation of nanoporous nickel by selective anodic etching of the nobler copper component from electrodeposited nickel-copper alloys

The preparation of nanoporous nickel films by electrochemical deposition of Ni-Cu alloy followed by the selective anodic etching of the less-active component (Cu) from the alloy was studied in an aqueous solution containing Cu(II) and Ni(II) at room temperature. Constant potential electrodeposition produced columnar Ni-Cu alloys, in which the Ni content increased as the deposition potential became more negative. X-ray diffraction and Auger mapping results indicate the presence of separated Cu-rich and Ni-rich phases in the alloys, with the Cu-rich phase being more concentrated in the middle of the column and surrounded by the Ni-rich phase. Cyclic voltammetric data indicates that anodic dissolution of nickel is retarded by passivation. By taking advantage of nickel passivation, selective anodic etching of copper from the Ni-Cu alloy produces nanohollow nickel tubes on indium-tin-oxide-coated glass substrates. The nanohollow tube structure obtained in this study is different from the interconnected bicontinuous nanopores that are usually obtained by dealloying the less noble component from a homogeneous solid solution alloy. The nanohollow tubes may have resulted from the fact that multiple phases columnar alloy deposits were produced by the electrodeposition step and from the limited mobility of nickel during the anodic etching step.