Electrodeposition of Cu-Zn and Cu-Mn Films As Precursors for Nanoporous Copper Synthesis

Abstract

An all-electrochemical approach for the synthesis of fine-structured nanoporous copper (np-Cu) films has been developed which involves the initial electrodeposition of Cu-containing alloys followed by a selective dissolution or dealloying of the less noble metal via anodization. This process leaves a nanoporous, three-dimensional spongy structure. Among these alloys are Cu-Zn and Cu-Mn that are commonly used as protective and decorative coatings. These types of coatings are typically rich in Cu; however, precursor alloys for dealloying purposes must contain high atomic percentages (at%) of the less noble metal. Here, we present the controlled electrodeposition of Cu-Zn and Cu-Mn alloys with Zn and Mn contents of ≥ 60 at% and ≥ 70 at%, respectively, as precursors for np-Cu synthesis.The co-electrodeposition of Cu-Zn and Cu-Mn alloys were achieved in baths containing pyrophosphate and ammonium sulfate, respectively. These electrolytes serve as a source of ligands that form complexes with Cu (i.e. [Cu(P2O7)]2- and [Cu(NH3) n ]2+). The use of the complexing agent is necessary to shift the reduction potential of Cu2+ negatively towards that of Zn2+ or Mn2+, thereby decreasing the large deposition potential difference between the two respective metals. The complexation of Cu in either bath was confirmed by voltammetric and spectroscopic studies.A systematic potentiostatic electrodeposition study revealed that the optimal plating potential for Cu-Zn is at -2.0 V vs. Hg/HgSO4 with an efficiency of 63–73%. At this potential, the alloy composition is tunable by adjusting the respective percent compositions of the Cu2+ and Zn2+ salts in the deposition bath, thereby producing highly crystalline, Zn-rich alloys that are suitable for dealloying purposes (1). For Cu-Mn, galvanostatic deposition at current densities of 100–200 mA⋅cm-2 gave crystalline deposits with low plating efficiencies (<30%) due to the concurrent hydrogen evolution reaction. Nonetheless, Mn-rich alloys were obtained by also varying the concentration ratio of the Cu2+ and Mn2+ salts in the ammine bath (2). The optimization of the Cu-Zn and Cu-Mn alloy plating parameters and conditions including the structural and compositional characterization will be discussed in detail.