BRUNO RIBEIRO DE MATOS

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Advancing direct ethanol fuel cell operation at intermediate temperature by combining Nafion-hybrid electrolyte and well-alloyed PtSn/C electrocatalyst
2021 - DRESCH, MAURO A.; MATOS, BRUNO R.; GODOI, DENIS R.M.; LINARDI, MARCELO; FONSECA, FABIO C.; VILLULLAS, HEBE de las M.; SANTIAGO, ELISABETE I.
The advancement of direct ethanol fuel cell (DEFC) represents a real challenge to electrochemical science because ethanol changes significantly the triple phase boundary properties such as the redox reactions and the proton transport. Ethanol molecules promote poor fuel cell performance due to their slow oxidation rate, reduction of the proton transport due to high affinity of ethanol by the membrane, and due to mixed potential when the ethanol molecules reach the cathode by crossover. DEFC performance has been improved by advances in the membranes, e.g., low ethanol crossover polymer composites, or electrode materials, e.g., binary/ternary catalysts. Herein, high temperature (130 °C) DEFC tests were systematically investigated by using optimized electrode and electrolyte materials: Nafion-SiO2 hybrid electrolyte and well-alloyed PtSn/C electrocatalyst. By optimizing both the electrode and the electrolyte in conjunction, DEFCs operating at 130 °C exhibited a threefold increase on performance as compared to standard commercially available materials.
Properties and DEFC tests of Nafion
2020 - MATOS, B.R.; GOULART, C.A.; TOSCO, B.; SILVA, J.S. da; ISIDORO, R.A.; SANTIAGO, E.I.; LINARDI, M.; SCHADE, U.; PUSKAR, L.; FONSECA, F.C.; TAVARES, A.C.
Nafion based composites are promising materials to improve the performance of direct ethanol fuel cells. In this work, composite membranes of Nafion and titanate nanotubes functionalized with sulfonic acid groups were prepared by melt-extrusion and tested in a direct ethanol fuel cell. Far and mid infrared spectroscopies evidenced the formation of ionic bridges between the sulfonic acid groups of both functionalized nanoparticles and the ionomer. Small angle X-ray scattering measurements revealed that the melt-extrusion method leads to an uniform distribution of the inorganic phase in the ionomer matrix. Such structural analysis indicated that the improved the proton conduction properties of the composites, even with the addition of a high concentration of functionalized nanoparticles, are an outcome of the synergistic ionic network due to the hydrid organic/inorganic proton conducting phases. However, an improvement of the fuel cell performance is observed for 2.5 wt% of functionalized titanate nanotubes, which is a result of the lower ethanol crossover and the plasticizing effect of the aliphatic segments of the organic moieties grafted at the surface of the titanate nanoparticles.
Palladium-based Electrocatalysts for Ethanol Oxidation Reaction in Alkaline Direct Ethanol Fuel Cell
2016 - MORAES, LETICIA P. R. de; MATOS, BRUNO R.; SANTIAGO, ELISABETE I.; FONSECA, FABIO C.; AMICO, SANDRO C.; MALFATTI, CELIA de F.
Direct ethanol fuel cells require adequate electrocatalysts to promote the carboncarbon cleavage of ethanol molecule. Typical electrocatalysts are based on platinum, which have shown improved activity in acidic media. However, Pt-based catalysts have high cost and are easily deactivated by CO poisoning. Therefore, novel catalysts have been developed, and among then, palladium-based materials have shown promising results for the oxidation of ethanol in alkaline media. The present study reports on the performance of alkaline direct ethanol fuel cel (ADEFC) by using carbon-supported Pd, PdSn, PdNi, and PdNiSn produced by impregnation-reduction of the metallic precursors. The effect of chemical functionalization by acid treatment of the carbon support (Vulcan) was investigated. The electrocatalysts were studied by thermogravimetric analysis (TGA), X-rays diffraction (XRD), transmission electron microscopy (TEM), cyclic voltammetry (CV), and ADEFC tests. TGA measurements of functionalized Vulcan evidenced the characteristic weight losses attributed to the presence of surface functional groups due to the acid treatment. A high degree of alloying between Pd and Sn was inferred from XRD data, whereas in both PdNi and PdNiSn, Ni occurs mostly segregated in the oxide form. TEM analyses indicated agglomeration of Pd and PdSn particles, whereas a more uniform particle distribution was observed for PdNi and PdNiSn samples. CV curves showed that the peak potential for the oxidation of ethanol shifts towards negative values for all samples supported on functionalized Vulcan indicating that ethanol oxidation is facilitated. Microstructural and electrochemical features were confirmed by ADEFC tests, which revealed that the highest open circuit voltage and maximum power density were achieved for PdNiSn electrocatalysts supported on functionalized Vulcan with uniform particle distribution and improved triple phase boundaries.
Properties and defc tests of nafion added functionalized titanate nanotubes prepared by extrusion
2016 - MATOS, B.R.; GOULART, C.A.; ISIDORO, R.A.; SILVA, J.S. da; SANTIAGO, E.I.; FONSECA, F.C.; TAVARES, A.C.
Composite electrolyte membranes based on the incorporation of a second inorganic phase into ionomer matrices such as Nafion revealed to possess enhanced properties such as increased mechanical resistance and reduced permeability of solvents. It has been reported that surface functionalized titanate nanotubes (H2Ti3O7.nH2O) display a proton conductivity of ~ 10-2 Scm-1, which is attractive for the use of such composites in direct ethanol fuel cells (DEFC). Herein, composite membranes based on the addition of sulfonic acid groups functionalized titanate nanotubes into Nafion matrix were prepared by grafting followed by extrusion. These membranes were characterized by infrared spectroscopy (FTIR), Brunauer–Emmett–Teller (BET), acid-base titration, proton conductivity measurements and DEFC tests. FTIR measurements confirmed both the grafting of the titanate nanotubes. BET measurements showed that the functionalized titanate nanotubes possess a high surface specific area. Acid-base titration evidenced that additional sulfonic acid groups are present in the composite membranes compared to the pristine ionomer. The conductivity measurements show that the increase in the titanate nanotube volume fraction into the ionomers has not resulted in a decrease of the proton conductivity. The results show that the addition of functionalized titanate nanotubes into Nafion polymer matrix resulted in an improvement of the electric transport properties, reduction of the fuel crossover and, consequently, a higher DEFC performance for the composites were observed with respect to the pristine Nafion.
Nafion-mesoporous silica composite electrolyte: properties and direct ethanol fuel cells performance
2016 - AHMED, Z.; MATOS, B.R.; FLORIO, D.Z. de; REY, J.F.Q.; SANTIAGO, E.I.; FONSECA, F.C.
Nafion-mesoporous silica composites were investigated aiming at improved performance of direct ethanol fuel cells (DEFC) operating at high temperature. Mesoporous silica (MPS) was synthesized by a sol–gel technique and added as the inorganic filler into Nafion membranes by casting process. The performance of DEFC using both Nafion and Nafion-MPS composites were evaluated by polarization curves and correlated to the electrical and structural properties of the electrolytes in ethanol environment inferred by impedance spectroscopy and small angle X-ray scattering, respectively. The main results show that Nafion-MPS composite electrolytes exhibit improved performance that was related to a structural pining of the ionic clusters of ethanol-saturated Nafion by the inorganic particles, which resulted in higher proton conductivity of the composite. The experimental results evidenced the relevance of a better understanding of the properties of Nafion-based electrolytes to further develop the direct alcohol fuel cells technology.
Performance enhancement of direct ethanol fuel cell using Nafion composites with high volume fraction of titania
2014 - MATOS, B.R.; ISIDORO, R.A.; SANTIAGO, E.I.; FONSECA, F.C.
The present study reports on the performance enhancement of direct ethanol fuel cell (DEFC) at 130 C with Nafion-titania composite electrolytes prepared by solegel technique and containing high volume fractions of the ceramic phase. It is found that for high volume fractions of titania (>10 vol%) the ethanol uptake of composites is largely reduced while the proton conductivity at high-temperatures is weakly dependent on the titania content. Such tradeoff between alcohol uptake and conductivity resulted in a boost of DEFC performance at high temperatures using Nafion-titania composites with high fraction of the inorganic phase.
Nafion-titanate nanotubes composites prepared by in situ crystallization and casting for direct ethanol fuel cells
2015 - MATOS, B.R.; ISIDORO, R.A.; SANTIAGO, E.I.; TAVARES, A.C.; FERLAUTO, A.S.; MUCCILLO, R.; FONSECA, F.C.
The physical properties relevant for the application of Nafionetitanate nanotubes composites in electrochemical devices such as water absorption capacity, ion conductivity, and thermal stability are reported. The nanocomposites were prepared by in situ hydrothermal conversion of anatase into titanate nanotubes in Nafion matrix and by casting of nanotube suspensions in Nafion. Composites were characterized by differential scanning calorimetry (DSC), dynamic vapor sorption (DVS), X-ray diffraction (XRD), transmission electron microscopy (TEM), proton conductivity, and tested in direct ethanol fuel cells (DEFC). Nafion etitanate nanotubes displayed higher water retention capacity in comparison with Nafion etitania composites as revealed by DSC and DVS. The ion conductivity at intermediate temperatures (80e130 C) for Nafionetitanate nanotube composites is higher than Nafion etitania composites indicating that the hydrophilicity and conduction properties of the titanate phase contributed to the improvement of the membrane electrical properties. The Nafionetitanate nanotube composites prepared by in situ solegel exhibited improved electric and electrochemical performance at high temperatures compared to the composite prepared by casting. The combined XRD, DSC, and TEM data indicated that at RH ¼ 100% Nafionetitanate nanotubes are thermally stable up to 130 C, but for higher temperatures the titanate nanotubes are converted to rutile nanorods.
High temperature opertion of direct ethanol fuel cells with Nafion-TiOsub(2) membranes and PtSn/C electrocatalysis
2009 - ISIDORO, R.A.; MATOS, B.R.; DRESCH, M.A.; SPINACE, E.V.; TRAVERSA, E.; FONSECA, F.C.; SANTIAGO, E.I.
NAFION - mesoporous silica as electrolyte for ethanol fuel cells
2009 - AHMED, ZAKARYA; MATOS, BRUNO R. de; FLORIO, DANIEL Z. de; LICOCCIA, SILVIA; TRAVERSA, ENRICO; ESPOSITO, VICENZO; FONSECA, FABIO C.; SANTIAGO, ELISABETE I.
Relação morfologia-propriedades elétricas de eletrólitos compósitos de Nafion para célula a combustível de alta temperatura
2012 - MATOS, BRUNO R. de
As células a combustível a etanol direto (DEFCs) são consideradas geradores de energia eficientes e de baixo impacto ambiental. O foco deste trabalho é avançar o entendimento sobre eletrólitos compósitos híbridos do tipo Nafion-cerâmica visando o aumento do desempenho das DEFCs operando em T ~ 130 °C. Partículas inorgânicas foram crescidas na matriz polimérica formando os compósitos Nafion-Sílica (NS), Nafion-Fosfato de Zircônio (NZ) e Nafion-Titânia (NT). Este último (NT) serviu como material precursor para a conversão in situ da titânia em nanotubos de titanato de hidrogênio por uma rota hidrotérmica alcalina assistida por micro-ondas (NNTH). A relação microestrutura-propriedades elétricas foi estudada por meio de medidas de espectroscopia dielétrica, análise dinâmico-mecânica, calorimetria diferencial exploratória e espalhamento de raios X em baixo ângulo. Estas técnicas contribuíram, por exemplo, para inferir a localização das partículas inorgânicas na estrutura multifásica do Nafion e estabelecer a sua influência nas propriedades gerais dos compósitos. Os resultados indicaram que as interações de repulsão eletrostática de longo alcance entre os grupos sulfônicos do Nafion hidratado provocam a transição conformacional das cadeias principais do estado enovelado para a conformação tipo bastão. Tal transição promove a redução da condutividade protônica e da estabilidade mecânica do Nafion para temperaturas acima da temperatura da relaxação (Tα ~ 110 °C), a qual pode ser deslocada para maiores temperaturas (T > 160 °C) nos compósitos híbridos. A interação das partículas de sílica e de titânia com a fase condutora do Nafion é maximizada, enquanto que as partículas de fosfato de zircônio estão localizadas majoritariamente nos domínios apolares. As interações entre os grupos sulfônicos do Nafion e as partículas de titânia contribuíram para a melhora das propriedades mecânicas em altas temperaturas e para a redução da permeabilidade ao etanol, as quais promoveram o aumento do desempenho da DEFC em altas temperaturas. A baixa permeabilidade ao etanol e as melhores propriedades termomecânicas e de transporte protônico dos compósitos NNTH refletiram em um elevado desempenho das DEFCs a 130 °C, evidenciando que estes eletrólitos compósitos são promissores para a aplicação pretendida.