Electrodeposition of CuNi Alloy Electrodes and their Use for the Reduction of Nitrate Ions in Alkali

Cu and Ni have the same crystal structure (face-centred cubic), similar valence, close values of atomic radii and electronegativity, and may form homogeneous solutions over the entire composition range. Given the potential advantages of a CuNi alloy in electrocatalytic applications - the components are common, cheap, relatively low toxicity metals - it appears interesting to electrodeposit alloys of different composition and morphology and test them in the reduction of nitrate for which the single metals display interesting performances. We have deposited CuNi alloys from citrate baths of suitable compositions, using: potentiostatic control and low current densities to obtain compact deposits (right figure, top); galvanostatic control and large current densities, ca. 3 A cm-2, to obtain macroporous electrodes (right figure, bottom) under a regime of vigorous H2 evolution in which the bubbles acted like a dynamic template. In comparison with similar Cu (and Ni) electrodes, compact Cu-rich alloys show superior performances in the reduction of nitrate - larger efficiency, better stability and higher selectivity towards NH3 production - at moderately negative electrode potentials [1]. Experiments performed in solutions of 0.1 M NaNO3 in 1.0 M NaOH, recorded at smooth and porous Cu80Ni20 electrodes (left figure), show a remarkably higher reduction current in the latter case, due to the larger active surface area and easy transport in the macropores.