ELECTRODESORPTION FROM SINGLE-CRYSTAL ELECTRODES - ANALYSIS BY DIFFERENTIAL ELECTROCHEMICAL MASS-SPECTROMETRY

A newly designed thin-layer cell allows the use of differential electrochemical mass spectrometry (DEMS) for the identification of volatile electrochemical desorption products from single-crystal electrodes. The sensitivity is in the range of a percent of a monolayer. This is demonstrated for the case of preadsorbed benzene on a Pt(111) electrode. Contrary to the case of a polycrystalline electrode, benzene is mainly desorbed as such without H/D exchange; only a minor part is hydrogenated to cyclohexane, which is the main desorption product from a polycrystalline electrode. Oxidation of the adsorbate occurs in two well-separated steps: In the double-layer region a partially oxidized adsorbed intermediate is formed, which is oxidized to CO2 in the oxygen adsorption region.