Banca de DEFESA: TUANI CARLA GENTIL

Uma banca de DEFESA de DOUTORADO foi cadastrada pelo programa.
STUDENT : TUANI CARLA GENTIL
DATE: 26/05/2023
TIME: 14:00
LOCAL: https://meet.google.com/esz-muic-atx
TITLE:

PALLADIUM-BASED NANOSTRUCTURED ELECTROCATALYST FOR APPLICATION IN ALKALINE DIRECT LIQUID FUEL CELLS

PAGES: 163
BIG AREA: Ciências Exatas e da Terra
AREA: Química
SUBÁREA: Físico-Química
SPECIALTY: Eletroquímica
SUMMARY:

Different types of anodic electrocatalysts palladium-based and low cost oxides were developed for application in alkaline direct liquid fuel cells (ADLFC). The electrochemical results of the acetol oxidation reaction (AOR) in an alkaline media were catalyzed by simple materials Pd-based supported on carbon, in which a mass activity of 193.8 mA mg^-1 Pd was obtained, using the PdNP/C material and 137.9 mA mg^-1 Pd using the commercial material Pd/C Alfa Aesar. In the operation studies in ADLFC, an open circuit voltage of 1341.3 mV was obtained using the PdNP/C material, higher than that found in the literature for alcohol oxidation, and a maximum power density of 31.6 mW cm⁻² at 80°C. High Tafel slope values were also obtained, suggesting a complexity of the mechanism and kinetics involved in the AOR process. Ethanol oxidation reaction (EOR) studies were initially catalyzed by simple materials based on Pd nanoparticles (NP) (PdNP/C), and by binary and ternary materials, which part of the high-cost metallic charge was replaced by Fe₃O₄ nano-octahedral and SnO₂ nanorods. The synthetic route success the in terms of obtaining controlled morphologies was evidenced by TEM. In the EOR studies, the PdNPFe₃O₄/C material resulted in the highest CV mass activity among the studied materials (1425.5 mA mg^-1 Pd), approximately twice as high as that obtained with the commercial material Pd/C AA and simple PdNP/C, followed by the PdNPSnO₂/C material (1134.9 mA mg^-1 Pd). The EOR chronoamperometry currents for the PdNPFe₃O₄/C electrocatalyst also outperformed the others, corroborating with the studies of linear scanning voltammetry in which the EOR Tafel exhibited the highest value of i₀, which may suggest a higher rate of electron transfer and increased electrocatalytic activity. Electrocatalysts based on Pd nanoparticles were tested in operation, constituting the anode of alkaline direct ethanol fuel cells (ADEFC), so that the most promising material was PdNPFe₃O₄/C, resulting in the highest power density value (31.4 mWcm^-2), at 70 °C, despite the 50% reduction in palladium load compared to the commercial and simple material. The PdNPSnO₂/C and PdNPFe₃O₄SnO₂/C materials also exhibited superior operation results in ADEFC than the commercial material (27.6 mWcm^-2 and 29.5 mWcm^-2, respectively, versus 17.7 mWcm^-2 obtained with Pd/C AA), also presenting a significant reduction of high-cost metal charge (approximately 45% for both materials in relation to the commercial one). Thus, it is suggested that the presence of Fe₃O₄ nano-octahedral (magnetite) and SnO₂ nanorods may favor the bifunctional mechanism, facilitating the oxidation of CO to CO₂, and, consequently, promoting an improvement in the catalytic activity for EOR. The presence of magnetite may also have caused the electronic effect, due to the magnetic properties of Fe₃O₄, which may reduce the interaction strength of intermediates that cause poisoning such as CO, corroborating the XRD results in which a lattice parameter variation was observed for the electrocatalyst PdNPFe₃O₄/C in relation to commercial material. In order to evaluate the effects of morphology on the catalytic activity of EOR in alkaline media, the materials mentioned above were synthesized again by varying the morphology of palladium, in which the same compositions were prepared, but with branched structures of Pd-nanodendrites (ND). The physical-chemical characterizations also showed the success of the synthesis, and the EOR results using these materials were promising in terms of mass activity in the CV, highlighting the material PdNDSnO₂/C (2366.1 mA mg^-1 Pd) even with the reduction of about 70% of the palladium load in its composition. This result corroborates the studies of operation in ADEFC, in which the PdNDSnO₂/C electrocatalyst performed better than all the others at operating temperatures from 50 °C to 70 °C, reaching a power density of 19.6 mWcm^-2, despite not surpassing the results using materials based on Pd-NP. To complement the study, the most promising material (PdNPFe₃O₄/C) was studied in stability tests, compared to commercial and simple material, in which advanced techniques of SFC-ICP-MS online and accelerated stress tests (AST) were used, both performed at the Helmholtz Institute Erlangen-Nürnberg (HI ERN) for Renewable Energy (Germany). The AST results showed that the PdNPFe₃O₄/C material resulted in a lower percentage of Pd dissolution and no Fe dissolution was observed, which was expected in an alkaline medium, in addition to the greater activity for EOR after AST compared to the simple material. Dissolution mappings recorded by SFC-ICP-MS online show that transient Pd dissolution begins during the forward scan at the fourth CV at the upper potential limit (UPL) of +0.9 V _RHE both in presence and absence of ethanol. Thus, it is suggested that the presence of Fe₃O₄ nano-octahedral contributed to the stability and activity of the material, corroborating with the electrochemical EOR studies and operation in ADEFC, showing promise in the area of electrocatalysis of ethanol oxidation for the use of alkaline direct ethanol fuel cells.

COMMITTEE MEMBERS:
Presidente - Interno ao Programa - 1544381 - MAURO COELHO DOS SANTOS
Membro Titular - Examinador(a) Interno ao Programa - 1544344 - VANI XAVIER DE OLIVEIRA JUNIOR
Membro Titular - Examinador(a) Interno ao Programa - 1544379 - ANDERSON ORZARI RIBEIRO
Membro Titular - Examinador(a) Externo à Instituição - JÚLIO CÉSAR MARTINS DA SILVA - UFF
Membro Titular - Examinador(a) Externo à Instituição - HAMILTON BRANDÃO VARELA DE ALBUQUERQUE - USP
Membro Suplente - Examinador(a) Interno ao Programa - 1766090 - MIRELA INES DE SAIRRE
Membro Suplente - Examinador(a) Externo ao Programa - 2604737 - EVERALDO CARLOS VENANCIO
Membro Suplente - Examinador(a) Externo à Instituição - SILVIA HELENA PIRES SERRANO - USP