Electrocatalytic oxidation of formaldehyde on gold studied by differential electrochemical mass spectrometry and voltammetry

The electrocatalytic oxidation of normal formaldehyde (CH2O) and deuterated formaldehyde (CD2O) 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 CO2 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. (C) 2001 The Electrochemical Society.