Electrochemical reduction of carbon dioxide is followed via cyclic voltammetry (cv) and on-line mass spectrometry (DEMS) at sputtered palladium in aqueous 0.1M KHCO3 solution. Carbon monoxide is detected as a volatile reduction product at potentials more negative than - 1.4V vs. Ag/AgCl. During the first potential scan consumption of carbon dioxide is already observed at -1 V vs. Ag/AgCl corresponding to a cathodic signal in cv. Flow cell experiments show that an adsorbate is formed at - 1 V. Carbon monoxide is generated from this adsorbate between - 1.4 and - 1.9 V. Oxidation of the adsorbate forming carbon dioxide is observed between 0.2 and 0.6 V. At - 1 V adsorbed CO/COOH is likely to be formed from carbon dioxide, inhibiting further CO2 reduction. Reduction of CO2 proceeds after desorption of the adsorbate at potentials below - 1.4V vs. Ag/AgCl.