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The anodic oxidation of formaldehyde on gold in alkaline aqueous solutions was studied by electrochemical impedance spectroscopy. One equivalent circuit was found to mimic all impedance spectra measured for normal formaldehyde and deuterated formaldehyde false(CD2Ofalse) in various alkaline solutions at various voltages. The resistors and capacitors constituting the circuit depend logarithmically on the voltage applied, and the circuit can be explained in terms of reaction steps proposed in the literature. A negative capacitance (inductive loop) was encountered at low frequencies, which is explained by a rate‐determining C‒H bond rupture step in the overall kinetics of the reaction, as it was more apparent for solutions containing CD2O instead of CH2O . Data were Kramers‐Kronig transformable and a χ2 ‐value of 10−4 or less was attained in all fits. At least four time constants were revealed by the impedance spectra as a result of positive capacitive, negative capacitive, resistive, and diffusive effects. © 1999 The Electrochemical Society. All rights reserved.

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 Ϫ25 and 60 kJ mol Ϫ1 confirming the highly catalytic properties of gold in the overall rate of the reaction.

It was found that long-lived, subnanometer-sized silver clusters can be prepared by anodic dispersion of a silver electrode in aqueous NaOH solutions (pH 10.5−12), free of stabilizing polymers. The method, described by Nouhuys in 1938, is based upon the application of a dc voltage (10−65 V) between two silver electrodes and yields a range of different clusters, colloids, and oxides. The large colloids and oxides can be removed by centrifugation leaving small colloids and clusters in the sols as revealed by the strong absorption of light at wavelengths between 210 and 400 nm. Absorption spectra of the sols remain fairly unchanged for weeks, implying the stabilization of the clusters by hydroxyl ions. Significant formation of the clusters is only observed between pH ∼10.5 and 12 and is explained by Joule heat generated in the Ag2O surface layer at the anode. At pH above 12, a passivating AgO layer forms, preventing the dispersion of clusters while no significant amounts of clusters form either at pH below 10.5 due to the absence of Ag2O at the surface.

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