DEMS studies on the adsorption of halogenated methane derivates led to the conclusion that those compounds adsorb as = CH2 or equivalent to CH species on Pt and Pd. Apart from those structures on Pt, a GO-like adsorbate which results from addition of water molecules or OH- ions is formed. The adsorbate can partially be desorbed at negative potentials by the formation of methane, ethane and a little butane. At anodic potentials the adsorbate is oxidized to CO2. The adsorption rate increases with the number of halogen atoms in the molecule. Moreover, it is dependent on the charge of the electrode or the competitive adsorption OH- anions. The transfer of the electrons during adsorption reaction was found not to be the rate-determining reaction step.