A three dimensional palladium-nucleophile electrode. Catalytic reduction of alkyl bromides at a voluminous palladium–iodide cathode

Evidence is presented that palladium electrodes (smooth metal or galvanostatic deposits from acidic solutions of Pd2+ onto several conducting substrates) may exhibit exceptional catalytic capabilities, especially with alkyl bromides if traces of iodide ions, used as dopants, are incorporated into the cathode matrix. The use of such chemically modified “surfaces” leads to important reduction potential shifts (ΔE > 1 V) compared to the use of glassy carbon. This intriguing catalytic behaviour may be attributed to the specific reactivity of palladium towards carbon–halogen bonds and to halogen exchange at the stage of the transient formed essentially inside the metal. Thus, such palladium-modified cathodes based only on halogen exchange can be useful for cleaving carbon–bromine bonds. Preliminary results have revealed that traces of iodide necessary for the catalytic process should be present inside the Pd bulk adjacent to the interface metal/liquid electrolyte interface. Since the process is catalytic in iodide, this kind of three dimensional electrode prevents the fast diffusion of I− off the bulk palladium and ensures a surprising long life for these doped, palladized interfaces. Different modes of doping by iodide salts are described, presumably through the formation of channels and fractals. An extension of this model of a 3D-Pd-nucleophile electrode can be proposed with other non-electroactive donors.