An electrocatalytic method of producing carbon nanotubes, comprising providing an electrocatalytic reactor comprising a supported catalyst selected from the group consisting of Fe, Cu, Ni, Mn, V, Zn, Co, Fe/Co, alkali metal doped Fe/Co, alkali metal doped Co and mixtures thereof, and supported on at least one support selected from the group consisting of yttria-stabilized zirconia supports, reticulated vitreous carbon foam supports, reticulated fibrous silicon carbide supports, zinc oxide foam supports, boron carbide supports, alumina, zirconia, and carbon, an adjacent barrier comprising a material permeable to oxygen ions and impermeable to at least CO 2, CO, H 2, H 2 O and hydrocarbons; contacting working and counter electrodes to opposite sides of the supported catalyst and the adjacent barrier; contacting the supported catalyst with a carbon-containing feedstock component comprising CO and optionally at least one member selected from the group consisting of CH 4, C 2 H 2, and C 2 H 4, and with a H 2 as a hydrogen-containing feedstock component under electrocatalytic conditions sufficient to reduce the carbon-containing feedstock component; applying a voltage across the working and counter electrodes and thereby biasing the barrier; heating the supported catalyst to a temperature ranging from 500 to 1000° C, producing carbon nanotubes at the surface of the supported catalyst, producing dioxygen at a side of the barrier opposite the supported catalyst, and removing dioxygen from the electrocatalytic reactor, wherein the barrier is sufficiently biased to conduct oxygen ions from a first side where the supported catalyst contacts with the carbon-containing feedstock component and the hydrogen-containing feedstock component to the side of the barrier opposite the supported catalyst. providing an electrocatalytic reactor comprising a supported catalyst selected from the group consisting of Fe, Cu, Ni, Mn, V, Zn, Co, Fe/Co, alkali metal doped Fe/Co, alkali metal doped Co and mixtures thereof, and supported on at least one support selected from the group consisting of yttria-stabilized zirconia supports, reticulated vitreous carbon foam supports, reticulated fibrous silicon carbide supports, zinc oxide foam supports, boron carbide supports, alumina, zirconia, and carbon, an adjacent barrier comprising a material permeable to oxygen ions and impermeable to at least CO 2, CO, H 2, H 2 O and hydrocarbons; contacting working and counter electrodes to opposite sides of the supported catalyst and the adjacent barrier; contacting the supported catalyst with a carbon-containing feedstock component comprising CO and optionally at least one member selected from the group consisting of CH 4, C 2 H 2, and C 2 H 4, and with a H 2 as a hydrogen-containing feedstock component under electrocatalytic conditions sufficient to reduce the carbon-containing feedstock component; applying a voltage across the working and counter electrodes and thereby biasing the barrier; heating the supported catalyst to a temperature ranging from 500 to 1000° C, producing carbon nanotubes at the surface of the supported catalyst, producing dioxygen at a side of the barrier opposite the supported catalyst, and removing dioxygen from the electrocatalytic reactor,