THE MECHANISM OF ELECTROCATALYTIC HYDROGENATION OF ORGANIC-MOLECULES AT PALLADIUM BLACK CATHODES

Voltammetry at rotating and stationary disc electrodes is used to assess the range of hydrogenation reactions possible at a palladium black cathode, prepared by electrodeposition onto graphite in an acid chloride bath. In addition, the mechanism of these electrocatalytic hydrogenations of organic molecules has been investigated. It is shown that methanol containing ethanoic acid as proton source is a convenient medium for electrocatalytic hydrogenation. At sufficiently negative potentials, the reduction of ethanoic acid becomes mass transport controlled and leads to absorbed hydrogen; it is shown that the Pd(H)/H+ couple is rapid and chemically reversible. The hydrogenation of the reactant occurs via a chemical step between the organic molecule and an active hydrogen species, probably an adsorbed hydrogen atom at the palladium surface and which may be regarded as an intermediate in the formation/oxidation of absorbed hydrogen.