Anodic oxidation of formaldehyde on gold studied by electrochemical impedance spectroscopy: An equivalent circuit approach

The anodic oxidation of formaldehyde on gold in alkaline aqueous solutions was studied by electrochemical impedance spectroscopy. One equivalent circu it was found to mimic all impedance spectra measured for normal formaldehyd e and deuterated formaldehyde (CD2O) in various alkaline solutions at vario us voltages. The resistors and capacitors constituting the circuit depend l ogarithmically 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 rea ction, as it was more apparent for solutions containing CD2O instead of CH2 O. Data were Kramers-Kronig transformable and a chi(2)-value of 10(-4) or l ess was attained in all fits. At least four time constants were revealed by the impedance spectra as a result of positive capacitive, negative capacit ive, resistive, and diffusive effects. (C) 1999 The Electrochemical Society . S0013-3651(98)06-078-9. All rights reserved.