Banca de DEFESA: VICTOR CRUZ DE SOUZA

Uma banca de DEFESA de MESTRADO foi cadastrada pelo programa.
DISCENTE : VICTOR CRUZ DE SOUZA
DATA : 25/06/2021
HORA: 14:00
LOCAL: Virtual
TÍTULO:

SAXS/XAFS in situ studies of thermal activated nucleation and the growth process of CsHSO4 in Nafion

PÁGINAS: 50
GRANDE ÁREA: Engenharias
ÁREA: Engenharia de Materiais e Metalúrgica
SUBÁREA: Materiais Não-Metálicos
ESPECIALIDADE: Polímeros, Aplicações
RESUMO:

The characterization of Nafion® - CsHSO4 composite electrolytes varying the temperature (T20 ºC - T160 ºC) was carried out through measurements of the X-ray scattering and absorption techniques: SAXS/XAFS, in order to obtain a fundamental microstructural study of the thermo-activation growth and nucleation process of CsHSO4 particles inside the Nafion® membrane, for the possible application of these Nafion® composite electrolytes - CsHSO4 in fuel cells of the type PEM (Proton Exchange Membrane) to operate at high temperatures ( > 120 ºC).
The high-temperature operation of the PEM cell brings benefits, such as the increase in the kinetics of electrode reactions, the increase in the diffusional transport kinetics in the electrodes and the increase in the
cell's tolerance to the carbon monoxide contaminant. Nafion®, a polymeric electrolyte commonly used in PEM cells has electrical conductivity dependent on the amount of water contained in its structure. In this way, the increase in the cell's operating temperature above 100 ºC causes the polymer to dehydrate and consequently markedly decrease its electrical conductivity. To increase the performance of electrolytes operating at high temperatures, a 0.5 mol / L solution of CsHSO4 was prepared and the Nafion® membrane was embedded in this
solution. The addition of CsHSO4 particles in the polymeric matrix of Nafion® aims to improve the electrolyte charge conduction conditions at elevated temperatures, since the CsHSO4 structure is known to undergo a
structural phase transition at slightly elevated temperatures (50-150 ºC), in which the conductivity of the proton jumps by several orders of magnitude. Through SAXS analyzes, varying the temperature, it was
evidenced that the thermo-activation process for the nucleation and growth of the CsHSO4 particles proved to be relevant from temperatures above 100 ºC, in which the growth of a peak in the region of the
membrane ionomer channel. With the analysis of the size of the ionomer channel with the increase in temperature, a kinetic model was created for the nucleation and growth of these particles. The XAFS analyzes
(XANES + EXAFS) showed that both the pre-edge profiles and the interatomic distances of the Cs element, in the K-space Fourier transform, did not show significant differences in the three thermal cycles exerted on the membrane, thus suggesting thermal stability for the entire system. The SAXS / XAFS results measured simultaneously, showed that the heating in the membrane until the temperature of 80 ºC
causes the characteristic peak of the ionomer channel to reduce its size and it was also possible to observe a change in the profile of the pre-edge of the Cesium element (Cs). 

MEMBROS DA BANCA:
Presidente - Interno ao Programa - 1669182 - JOSE FERNANDO QUEIRUGA REY
Membro Titular - Examinador(a) Interno ao Programa - 2604128 - ALEXANDRE JOSE DE CASTRO LANFREDI
Membro Titular - Examinador(a) Externo à Instituição - Santiago Jose Alejandro Figueroa - CNPEM
Membro Suplente - Examinador(a) Interno ao Programa - 1761120 - DANILO JUSTINO CARASTAN
Membro Suplente - Examinador(a) Externo ao Programa - 1982740 - GUSTAVO MORARI DO NASCIMENTO