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| Author(s): |
Leandro Cesar Trevelin
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | São Carlos. |
| Institution: | Universidade de São Paulo (USP). Instituto de Química de São Carlos (IQSC/BT) |
| Defense date: | 2021-01-18 |
| Examining board members: |
Marcos Roberto de Vasconcelos Lanza;
José Mario de Aquino;
Fernando Cruz de Moraes;
Lucia Helena Mascaro Sales
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| Advisor: | Marcos Roberto de Vasconcelos Lanza; Robson da Silva Rocha |
| Abstract | |
Electrosynthesis of hydrogen peroxide is the result of oxygen reduction reaction. This reaction can be expressed by two distinct mechanisms, reduction of molecular oxygen via 2- electrons pathway for formation of H2O2, or the oxygen molecule present in solution can reduce via 4-electrons pathway for the formation of H2O. In the present study, the Printex 6L carbon modification process was developed with the addition of mixed oxides of Niobium, Tungsten, Zirconium and Palladium, in a first stage and evaluated the electroactivity of Printex L6 carbon - graphene oxide composites in three different electrolytes - 0.1 mol L-1 KOH (pH= 12.8), 0.1 mol L-1 K2SO4 (pH= 5.8) and 0.1 mol L-1 K2SO4 (acidified with H2SO4 for pH 2) in a second one. In the first stage, the materials were synthesized based on the polymeric precursor method and the physical characterization was performed by x-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The electrochemical analysis of the materials used electroanalytical techniques such as cyclic voltammetry, chronoamperometry and linear sweeping voltammetry, and the best results showed that 1% niobium oxide and tungsten, 1% molybdenum oxide and zirconium and 1% zirconium oxide and palladium reached 83.5%, 77.7% and 82.3% of current efficiency for the generation of H2O2, respectively, but in more positive potentials than carbon without modification, reaching approximately 200 mV, 400 mV and 650 mV of displacement of potential for more positive, in relation to the 84.2% obtained for printex 6L carbon. In the second stage the Printex L6 carbon - graphene oxide composites catalysts were prepared by mixing Printex L6 carbon black with electrochemically exfoliated graphene oxide in a mass ratio varying between 0 and 100 wt%. Morphological, structural and electrochemical characterization of the composites were studied comparing the electroactive surface area by cyclic voltammetry, surface area and pore size estimated by BET and resistivity of the materials showing was correlated to a better dispersion of PLCB within the EGO sheets, consequently exposition of active sites for ORR in the basal plane of the EGO sheets. The catalyst, composed of 75 wt% PLCB and 25 wt% of EGO showed the best electrochemical performance for ORR, with a shift of the half-wave of potential of ca. 160 mV in 0.1 mol L-1 KOH (pH= 12.8), ca. 120 mV in 0.1 mol K2SO4 (pH= 5.8) and ca. 100 mV in 0.1 mol L-1 K2SO4 (pH= 2) compared with pure Printex L6. (AU) | |
| FAPESP's process: | 16/12597-0 - Gas difusion electrodes production modified with bimetallic oxides of Nb, Mo, Pd e Zr for the production of H2O2 in situ |
| Grantee: | Leandro Cesar Trevelin |
| Support Opportunities: | Scholarships in Brazil - Doctorate |