Reaction pathway of four-electron oxidation of formaldehyde on platinum electrode as observed by in situ optical spectroscopy

When a platinum electrode is dipped into aqueous sulfuric acid solution containing formaldehyde, the surface is covered by CO, which is formed by the dissociative adsorption of formaldehyde. A second harmonic generation voltammogram pumped by a 532 nm laser pulse and photo-reflectance voltammogram probed by a 670 nm laser beam are sensitive to the surface CO and surface oxide, respectively. The experiments demonstrate that the anodic oxidation pathway of the formaldehyde through CO adsorption proceeds by coupling with the surface oxide formation and that the CO controls the dual reaction pathway, the anodic and cathodic path of the reaction, and induces a non-linear self-sustained oscillation. The kinetics of the dissociative adsorption is discussed based on the time course of the current induced by the laser desorption of CO. (C) 1997 Elsevier Science B.V.