The partial oxidation of iso-butane to methacrolein over an inert gold electrode was studied at 425 to 475 degrees C, in an electrochemical membrane reactor using yttria-stabilized zirconia as a solid electrolyte. On applying an external current to the reaction cell, methacrolein was formed at the gold anode with a selectivity of 13 to 19%, depending on the reaction conditions. The formation rate of methacrolein increased linearly with the applied current, while no methacrolein was formed when dioxygen was used as the oxidant. This indicates that iso-butane is oxidized to methacrolein by oxygen species produced electrochemically at the gold-YSZ-gas-phase three-phase boundary.