Electrocatalytic Oxidation of Formaldehyde on Gold Studied by Differential Electrochemical Mass Spectrometry and Voltammetry

The electrocatalytic oxidation of normal formaldehyde ( CH 2 O ) and deuterated formaldehyde ( CD 2 O ) has been studied on gold in aqueous, alkaline solution as a function of pH, concentration, potential, and temperature by voltammetry, chronoamperometry, and differential electrochemical mass spectrometry. The H 2 , D 2 , and CO 2 gas evolution kinetics depend to great extent on the pH, potential, and temperature but play a minor role in the overall rate of the electro-oxidation reaction. The evolution of hydrogen at the open-circuit potential and the current efficiencies larger than 100% pointed toward the occurrence of a nonelectrochemical dehydrogenation reaction parallel to the electro-oxidation reaction. The kinetic isotope effects and activation energies suggested that the overall rate of the electro-oxidation reaction is determined by the hydroxyl catalyzed, enthalpy-driven, chemisorption of the enolate anion at low potentials, by the entropy-driven desorption of the formate anion at higher potentials, and by diffusion at the highest potentials. The apparent activation energies ( E a ) ranged in value between −25 and 60 kJ mol − 1 confirming the highly catalytic properties of gold in the overall rate of the reaction.