Modification of surface activity of Cu–Zr amorphous alloys and Cu metal by electrochemical methods

This paper summarizes our attempts to use some strictly controlled electrochemical processes of dissolution/redeposition of Cu (including disproportionation of Cu+ to Cu metal and Cu2+) to modify Cu surfaces, as well as surfaces of Cu base amorphous alloys (AA), to produce active substrates for various phenomena of adsorption and catalytic reactions. We developed some new methods of activation of the Cu substrate for in situ investigations of adsorbates with SERS (Surface Enhanced Raman Spectroscopy). The first method developed produced an oxidized Cu surface. A distinct spectral shift of the bands characteristic of the adsorbate was observed, due to its interaction with Cu2O instead of interacting with metallic Cu. The second method produced a substrate with a clean surface and large specific surface area which resulted in a high quality SERS spectrum exhibiting a 10-fold increase in the signal-to-noise ratio, compared to the results for the surface pretreated by commonly used methods of surface roughening (oxidation–reduction cycling). The third method included an irreversible, diffusion-controlled Cu deposition onto a substrate and resulted in a rather complex, partially oxidized substrate with Cu clusters exhibiting a variety of SERS activities. The second method appeared also useful for the modification of the surface activity of Cu–Zr amorphous alloys. This method was combined with an ageing process of the AA to produce a partial devitrification of the substrate. The electrochemical pretreatment was then applied after this partial devitrification. The catalytic efficiency for dehydrogenation of 2-propanol on such a pretreated Cu–Zr substrate increased by a factor of two. A correlation has been found between the SERS activity of an electrochemically pretreated substrate and its catalytic efficiency. A tentative mechanism of surface activation is discussed.