Investigation of the oscillatory electro-oxidation of formaldehyde on Pt and Rh electrodes by cyclic voltammetry, impedance spectroscopy and the electrochemical quartz crystal microbalance

Abstract

The oscillatory oxidation of formaldehyde is studied on platinum and rhodium polycrystalline electrodes in alkaline and acidic solutions. Both potentiostatic current and galvanostatic potential oscillations are found under most circumstances, except in alkaline solution on platinum where only current oscillations are found and no potential oscillations. The role of a sufficiently large series resistance (either internal or external to the cell) is shown to be essential in the generation of the potentiostatic current oscillations. The main destabilizing process in both systems is shown to be a (hidden) negative faradaic impedance, which is identified by impedance spectroscopy. Surface mass measurements with an electrochemical quartz crystal microbalance demonstrate the important role of oxide layer formation in the oscillations. The results are discussed in relation with earlier mechanistic studies of the formaldehyde electro-oxidation.