Direct oxygenation of aromatics to phenols, C6 alkanes and light alkanes to alcohols and aldehydes are realized at the cathode during H-2-O-2 fuel cell reactions at room temperature. The advantages of these H-2-O-2 fuel cell systems compared with the common catalytic oxidation systems are demonstrated and the electrocatalysis of the cathodes and the reaction mechanisms for the oxygenations are discussed in detail. The topics are the omega-oxidation of n-hexane with (FeCl3 + alpha-cyclodextrin)/graphite cathode, the synergism of Pd-black and iron compounds for the formation of phenol on (Pd-black + Fe3O4)/carbon-whisker (CW) cathode, cogeneration of phenol and electricity by using CuSO4/CW cathode, the synergism of different carbon materials in the cathode for the product selectivity in the oxidation of toluene on (CW + Active Carbon) cathodes, and the oxidation of propane over (Pd-black + VO(acac)(2))/carbon-fiber cathodes in the gas phase. Reductive activation of oxygen on the cathode is essential for these oxygenations. For most of the electrocatalytic systems used in this work, the oxygenations of alkanes and aromatics can be explained on the basis of Fenton Chemistry assuming HO. as the active oxygen species, except for the SmCl3/graphite cathode. (C) 2000 Elsevier Science B.V. All rights reserved.