Electrodeposition of Cu-Mn Films as Precursor Alloys for the Synthesis of Nanoporous Cu

Abstract

Cu-Mn alloy films are electrodeposited on Au substrates as precursor alloys for the synthesis of fine-structured nanoporous Cu structures. The alloys are deposited galvanostatically in a solution containing ammonium sulfate, (NH4)2SO4, which serves as a source of the ammine ligand that complexes with Cu, thereby decreasing the inherent standard reduction potential difference between Cu and Mn. The formation of the [Cu(NH3)n]2+ complex was confirmed by UV-Vis spectroscopic and voltammetric studies. Galvanostatic deposition at current densities ranging from 100 to 200 mA⋅cm−2 generally resulted in the formation of type I, crystalline coatings as revealed by scanning electron microscopy. Although the deposition current efficiency is (<30%) generally low, the atomic composition (determined by energy dispersive X-ray spectroscopy) of the deposited alloys range from 70–85 at% Mn, which is controlled by simply adjusting the ratio of the metal ion concentrations in the deposition bath. Anodic stripping characterization revealed a three-stage dissolution of the deposited alloys, which suggests control over the selective removal of Mn. The composition of the alloys obtained in the studies are ideal for electrochemical dealloying to form nanoporous Cu.

Porosity evolution and oxide formation in bulk nanoporous copper dealloyed from a copper–manganese alloy studied by in situ resistometry

“…Similar types of geometric features have been described in the literature before, for dealloyed CuMn. For example, Chen et al 28 identied nanocube and spheroid nanoparticles aer dealloying as Cu 2 O. Castillo et al 32 found that manganese oxide forms nanoplatelets during etching of electrodeposited CuMn which is supported by Biswal et al 57 who stated that MnO 2 can be electrodeposited from Mn 2+ in HCl by rst oxidation of Mn 2+ to Mn 3+ .…”

“…The high chemical reactivity of both copper and manganese makes the (electro-)chemistry of these systems highly complex. For example, pronounced oxide formation of both alloy components has been reported 25,32 but a full understanding of the underlying kinetics is still missing. At the same time, deliberate control of oxide formation is of great importance for many applications including energy storage and sensing.…”

“…Up to now, only a few studies are available which focus on the systematic understanding of the dealloying of this alloy system. Early investigations on the dealloying process and the porous structure of copper manganese alloys started in the 1980s, [29][30][31] but studies on microstructural composition of the porous structure 32,33 or electrocatalytic performance 13,25 have been performed only in recent years. Also, strong inuence of the pH-value and concentration 26,28,34 of the electrolyte as well as of previous heat treatment 35 has been reported.…”