Complex Dynamics in the Electro-Oxidation of Formic Acid Assisted by Hydrazine in Acidic Media

Abstract

Formic acid and hydrazine are both molecules of energetic interest as they can be used in devices such as fuel cells. Much has been done toward the elucidation of the mechanism of their electro-oxidation separately but less using hydrazine as additive to formic acid. In this paper we characterize the complex behavior that emerges when electro-oxidizing formic acid assisted by hydrazine. All results were obtained by means of traditional electrochemical techniques such as voltammetry, chronoamperometry and chronopotenciometry. In comparison to the dynamics of the oscillatory electro-oxidation of formic acid, the oscillations observed for the assisted system were more stable, more durable, with a smaller poisoning rate and also with a higher mean potential. The system was characterized as hidden negative differential resistance type and two different regions for potentiostatic oscillations were found. The role played by hydrazine was attributed to its interaction with oxygenated species at the platinum surface. The open circuit reduction of platinum oxide for the assisted system proceeds faster when compared to formic acid alone. Altogether, the experimental strategy used helped elucidating some mechanistic aspects and to suggest that the interaction of hydrazine and platinum oxide could be the main feature causing the differences in the oscillations.