Formation of intermediates during methanol oxidation: A quantitative DEMS study

Current efficiencies for the formation of CO2 during methanol oxidation at smooth polycrystalline platinum electrodes were determined by differential electrochemical mass spectrometry in a thin layer flow through cell. In all cases, the current efficiencies are below 60%; in particular, values as lo w as 16% were found in 0.1 M methanol solution at 0.6 V, which shows that a large amount of soluble intermediates (formaldehyde and/or formic acid) ar e formed. The extent to which these soluble intermediates are further oxidi zed to CO2 depends on the diffusion conditions. For methanol oxidation a pa rallel oxidation path via COad is also active. The influence of the surface crystal structure and, in particular, of steps was also studied. Step deco ration by foreign metals allowed examination of the effect of cocatalytic m etals on well defined model surfaces.