Controlled-potential reductions of primary alkyl halides (RX, where X=Cl, Br, or I) have been carried out at smooth and at platinized platinum electrodes in dimethylformamide containing tetramethylammonium tetrafluoroborate (TMABF(4)) under super-dry conditions ([H2O] <3 mM). Product distributions depend on the state of the electrode and on the potential employed for an electrolysis. For example, at a freshly platinized platinum gauze electrode, reduction of bromoethane or 1-bromopropane at -2.5 V vs. saturated calomel electrode (SCE) and of 1-chloropropane at -2.8 V vs. SCE affords the corresponding alkene in nearly quantitative yield (>96%). On the other hand, electrolysis of 1-iodobutane at -2.2 V vs. SCE and at a platinized platinum cathode gives 1-butene and butane in essentially a 1:1 ratio. These observations, buttressed by additional data derived from scanning electron microscopy and cyclic voltammetry, can be explained by the formation of an ionometallic layer, (Pt-n(-) TMA(+), TMABF(4)), on the surface of the platinum cathode at a potential for which there is concomitant reduction both of RX and of traces of water (to produce hydroxide ions within the layer). Thereafter, the resulting surface-modified platinum electrode (with a strongly basic character) acts catalytically via an E2 process to form an alkene from a primary alkyl halide. (C) 2004 The Electrochemical Society.