Modification of surface activity of Cu-Zr amorphous alloys and Cu metal byelectrochemical methods

This paper summarizes our attempts to use some strictly controlled electroc hemical processes of dissolution/redeposition of Cu (including: disproporti onation of Cu+ to Cu metal and Cu2+) to modify Cu surfaces, as well as surf aces of Cu base amorphous alloys (AA), to produce active substrates for var ious phenomena of adsorption and catalytic reactions. We developed some new methods of activation of the Cu substrate for in situ investigations of ad sorbates 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 produ ced 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 t he signal-to-noise ratio, compared to the results for the surface pretreate d by commonly used methods of surface roughening (oxidation-reduction cycli ng). The third method included an irreversible, diffusion-controlled Cu dep osition onto a substrate and resulted in a rather complex, partially oxidiz ed substrate with Cu clusters exhibiting a variety of SERS activities. The second method appeared also useful for the modification of the surface acti vity of Cu-Zr amorphous alloys. This method was combined with an ageing pro cess of the AA to produce a partial devitrification of the substrate. The e lectrochemical pretreatment was then applied after this partial devitrifica tion. 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 sub strate and its catalytic efficiency. A tentative mechanism of surface activ ation is discussed. (C) 1999 Elsevier Science S.A. All rights reserved.