Effects of the Fe content in Fe/C-N electrocatalysts in the activity and selectivity of the carbon dioxide reduction reaction

Author(s)

Vitória Pistori Guimarães

• Document type: Master's Dissertation
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT)
• Defense date: 2021-11-30

Examining board members

Edson Antonio Ticianelli; Mônica Helena Marcon Teixeira Assumpção; Janaina Fernandes Gomes

• Advisor: Edson Antonio Ticianelli

Abstract

Currently, non-renewable energy sources, especially fossil fuels, are dominant in the global energy matrix and this is the cause of several environmental problems, one of them being the emission of carbon dioxide (CO2) that has reached alarming levels in recent years. A promising approach to reduce this emission is the use the CO2 excess in electrochemical reduction systems to produced value added products. In this scenario, the present work aims to study the CO2 reduction reaction (CO2RR), in a neutral solution of KHCO3 0,1 M saturated with CO2. Reaction electrocatalysts are based on nitrogen-doped carbon materials containing iron (Fe/C-N), prepared from carbon powder impregnated with different proportions of the Fe complex Fe[2,4,6-Tris(2-pyridyl)-1,3,5-triazine]22+ (Fe[TPTZ]22+), followed by pyrolysis under N2 or NH3 atmospheres, so to obtain nitrided-carbon materials with Fe contents between 1 to 20 wt.% (wt. percent). Characterization of the produced materials was performed by thermogravimetric analysis (TG), X ray diffraction (XRD), Raman spectroscopy, scanning and transmission electron microscopy (SEM and TEM), associated with energy dispersive X ray spectroscopy (EDS) and X ray photoelectron spectroscopy (XPS). Results have shown that 10 wt.% of the initial TPTZ content remained in the sample and that a fraction of the nitrogen contained in this product is fixed in the carbon powder atoms network, with contents consistent with the Fe nominal formulations, but also evidencing the presence of FeN and Fe3O4. Electrochemical studies involved cyclic voltammetry associated to a rotating ring-disk electrode (RRDE), for rapid detection of RRCO2 products formed in the disk by the ring. Operational tests of the RRDE system were initially performed using Au disk and Pt. The analysis in the Pt ring of the products generated in the disk containing the catalysts indicates formation of a product different than for the Au disk, and evidenced production of formate ions, instead of CO. The estimated faradaic efficiency demonstrated better performance of the material with 1 wt.% of Fe, with high specificity to the formate product in all cases. (AU)

• FAPESP's process: 19/04700-3 - Effects of the dispersion and Fe content on Fe/C-N electrocatalysts in the selectivity of the carbon dioxide reduction reaction
• Grantee: Vitória Pistori Guimarães
• Support Opportunities: Scholarships in Brazil - Master