Ahstraet-The influence of acetonitrile on both the adsorption and electro-oxidation of CO at smooth and rough platinum in 0.1 M HClO, has been investigated with the help of on-line electrochemical mass spectrometry (DEMS). It is shown that a small amount of acetonitrile (AN) in solution catalyzes strikingly the bulk electro-oxidation of CO. The catalytic effect is much higher on smooth than on rough platinum surfaces. The catalytic activity also depends upon the concentration of AN, for a smooth Pt surface below O.OlM. However, the electro-oxidation of CO adsorbates is seriously inhibited by the presence of AN in solution.
The interaction between the surface species derived from AN and CO was studied in great detail. The results show that the adsorption of CO obviously can still proceed by removing parts of preadsorbed AN. On the other hand, the adsorption of AN is completely inhibited on the surface previously covered with a monolayer of CO,. When both, AN and CO, are present simultaneously in solution, co-adsorbed surface species are formed at the electrode surface. We think that the enhanced electro-oxidation of CO is due to a "third body" effect modified by a special adsorption/desorption behaviour of AN.