RODRIGO PIRES DA SILVA
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Artigo IPEN-doc 30769 Optimized interfaces for PBI-based high-temperature direct ethanol fuel cells2024 - SILVA, RODRIGO P. da; MATOS, BRUNO R. de; FONSECA, FABIO C.; SANTIAGO, ELISABETE I.The present study combines innovative strategies aiming at enhanced performance of direct ethanol fuel cells (DEFC) by modifying interfaces at both electrodes and electrolyte. Increasing the operating temperature to 180 °C to promote faster kinetics and thermally activated processes taking place in DEFC was possible by using phosphoric-acid-doped PBI (polybenzimidazole) composite electrolytes. The properties of the PBI electrolytes were improved by adding SiO2 as an inorganic second phase, promoting an increase in the proton conductivity and inhibiting ethanol crossover. Optimizing electrode reactions by increasing the triple-phase boundary was demonstrated by using a powdered-based PBI “ionomeric” concept to boost the performance of the proton exchange membrane fuel cell. The electrochemical characterization of the high-temperature direct ethanol fuel cells (HT-DEFC) showed that combining the strategies for the optimized electrode and electrolyte was crucial for increasing the performance of membrane electrode assemblies operating at 180 °C.Artigo IPEN-doc 27193 SAXS signature of the lamellar ordering of ionic domains of perfluorinated sulfonic-acid ionomers by electric and magnetic field-assisted casting2020 - SILVA, JAQUELINE S. da; CARVALHO, SABRINA G.M.; SILVA, RODRIGO P. da; TAVARES, ANA C.; SCHADE, ULRICH; PUSKAR, LJILJANA; FONSECA, FABIO C.; MATOS, BRUNO R.At present, small angle X-ray scattering (SAXS) studies of perfluorinated sulfonic-acid ionomers (PFSAs) are unable to fully determine the true shape of their building blocks, as recent SAXS modelling predicts disk- and rod-like nanoionic domains as being equally possible. This scenario requires evidence-based findings to unravel the real shape of PFSA building blocks. Herein, a SAXS pattern signature for a lamellar nanophase separation of the ionic domains of Nafion is presented, backed by mid and far infrared spectroscopy (MIR and FIR) and wide angle X-ray scattering (WAXS) data of Nafion in different ionic forms, a broad range of ionic phase contents (EW ~ 859–42 252 g eq-1) and temperatures. The study indicates that the lamellar arrangement of the ionic domains is the most representative morphology that accounts for the physical properties of this ionomer. The lamellar SAXS reflections of Nafion are enhanced in electric and magnetic field-aligned membranes, as confirmed by atomic force microscopy (AFM). Electric and magnetic field-assisted casting of Nafion allowed producing nanostructured and anisotropic films with the lamellas stacked perpendicularly to the field vector, which is the direction of interest for several applications. Such nanostructured Nafion membranes are bestowed with advanced optical and proton transport properties, making them promising materials for solar and fuel cells.