N-Shaped Negative Differential Resistance in the Oxidation of Methanol on Platinum in the Absence of Water

Abstract

We have reported that the methanol oxidation on Pt electrode produces a large current in the absence of water (Electrochim. Acta, 136, 385 (2014)). The amount of adsorbed CO decreases at a high potential, leading us to postulate that adsorbed CO reacts with methanol to form methyl formate to produce vacant sites, where methanol is oxidized to form methyl formate or formaldehyde. The methanol oxidation exhibits potential oscillations in the absence of water. This indicates that there exists an N-shaped negative differential resistance (N-NDR), leading us to postulate that the adsorbed methanol acts both as a site blocker and as a reactant. In this present work, to verify these postulations, we study the methanol oxidation by using liquid chromatography and measuring electrochemical impedance spectroscopy. Furthermore, we suggest that the adsorption of methanol on Pt, which is the first elementary step of the oxidation, is responsible for the N-NDR.