Formic acid electro-oxidation assisted by hydrazine

Author(s)

Eduardo Giangrossi Machado

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2017-01-09

Examining board members

Hamilton Brandão Varela de Albuquerque; Antonio Carlos Dias Angelo; Elton Fabiano Sitta; Ernesto Chaves Pereira de Souza

• Advisor: Hamilton Brandão Varela de Albuquerque

Abstract

Recently, the mechanism by which formic acid is oxidized is a matter of debate on the literature. There is disagreement on the pathways that the process may occur as well as which would be the intermediates participating. In this sense, there are some work exploring another aspect of this reaction, such as its behavior facing the addition of an additive. Among them, hydrazine has been chosen as it is another molecule of interest for energy generation devices such as fuel cells. In this fashion, it is argued that the presence of hydrazine would not interfere in the electro-oxidation of formic acid and, therefore, would yield an additive current when being co-oxidized. The complex behavior of a system may display new and relevant information thus this methodology was employed to revisit this system. It was found that the system would behave, instead of the argued additive behavior, synergistically and that there are striking differences on the time-series of formic acid, such as an increase on the duration of the process and the alteration of some of its variables. Also, it was observed a change in the potentiostatic oscillations, showing a dependence of the process with the morphology of the surface employed. It was proposed that hydrazine would act reducing the accumulation of oxygenated species on the surface of the electrode, postponing the end of the time-series. Next, it was employed a spectrometric technique (DEMS) to evaluate the production of gaseous products (CO2) and it was found that, in the presence of hydrazine, formic acid gets oxidized in a more facile way, in lower overpotential values. It was proposed that, besides preventing the accumulation of oxygenated species, hydrazine would disturb the decomposition of formic acid to COads, allowing a direct oxidation in lower overpotentials. Finally, for deepening the understanding of the superficial processes it was employed an imaging technique (EMSI). It was discovered that the decomposition of formic acid to COads there is a reactional front that repeats itself cycle after cycle during the time-series and that it is possible to monitor changes in the coverage of adsorbates by changes in the intensity of the image. It was not possible to obtain data in the presence of hydrazine since it generates many bubbles that disrupt the experiment. As conclusion of this work it is presented the thesis that, with the amount of evidences herein presented, the interaction between formic acid and hydrazine is synergistical rather than additive, as stated on the literature. (AU)

• FAPESP's process: 12/07313-1 - Electro-oxidation of mixed fuels: kinetical instabilities and mechanism
• Grantee: Eduardo Giangrossi Machado
• Support Opportunities: Scholarships in Brazil - Doctorate