ROBERTA ALVARENGA ISIDORO

ROBERTA ALVARENGA ISIDORO

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Improving the electrocatalytic activities and CO tolerance of Pt NPs by incorporating TiO2 nanocubes onto carbon supports
2021 - ANTONIASSI, RODOLFO M.; QUIROZ, JHON; BARBOSA, EDUARDO C.M.; PARREIRA, LUANNA S.; ISIDORO, ROBERTA A.; SPINACE, ESTEVAM V.; SILVA, JULIO C.M.; CAMARGO, PEDRO H.C.
Designing efficient anode CO-tolerant electrocatalysts is critical in low-temperature fuel cell catalysts fueled either by H2/CO or alcohol. We demonstrate that the incorporation of TiO2 nanocubes (TiO2NCs) on Carbon Vulcan supports, followed by the synthesis of Pt NPs at their surface (Pt/TiO2NCs-C material), led to improvements in performance towards the electrooxidation of carbon monoxide, ethanol, methanol, ethylene glycol, and glycerol in acidic media relative to the commercial Pt/C and Pt/TiO2-C counterparts employing commercial TiO2. The nanocubes enabled changes in the electronic properties of Pt NPs while contributing to the bifunctional mechanism as compared to Pt/C and Pt/TiO2-C with commercial TiO2. Fuel cell experiments fed with H2/CO steam showed that Pt/TiO2NCs-C employing nanocubes was resistant to CO-poisoning, yielding superior performance in operational conditions. The results reported herein have important implications for developing electrocatalysts with superior performances in PEMFCs.
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.
Advances on Nafion-based composites for high temperature proton exchange membrane fuel cells
2017 - SANTIAGO, ELISABETE I.; MATOS, BRUNO R.; DRESCH, MAURO A.; ISIDORO, ROBERTA A.; FONSECA, FABIO C.
PEMFC (Proton exchange membrane fuel cell) is considered a promising and efficient hydrogen fuelled electrical power source. However, PEMFC faces several technical problems, such as sluggish electrode reaction kinetics involving the limiting rate of the oxygen reduction and alcohol oxidation reactions, and high resistance to ion transport that could be surpassed with increasing of the operation temperature. The main impediment for such a temperature increase is the water dependent performance of the state-of-the-art Nafion electrolyte. Above 80 ºC water starts to evaporate considerably and Nafion microdomains begin to shrink, disrupting its percolative structure, leading from a conductor to insulator transition. In this work, the incorporation in-situ or ex-situ of an inorganic phase with hydrophilic properties, such as TiO2 and SiO2, into Nafion membranes has been evaluated as an interesting alternative to produce stable electrolytes able to operate at higher temperatures (130o C). The physical-chemistry and electrochemical characterisation has shown that the inorganic particles located in both the nonionic and ionic regions of the ionomer have important contributions to enhanced thermal stability and water uptake. Such features resulted in significant improvements of the PEMFCs using composite electrolytes tested at high operating temperature and low relative humidity. In addition, remarkable enhancement on the DEFC (Direct Ethanol Fuel Cell) performance (122 mW cm‑2) has been obtained as a result of an increase of ethanol oxidation reaction rate promoted by the combination of enhanced catalyst activity and high temperature of operation using stable composite Nafion-SiO2 electrolytes.
CoNi/C electrocatalysts for alkaline fuel cell
2018 - ISIDORO, ROBERTA A.; SANTOS, GABRIEL S. dos; FONSECA, FABIO C.
Solid alkaline fuel cell (SAFC) has been studied as possible alternatives in the production of electricity for portable and stationary applications. The oxygen reduction reaction (ORR) is key electrochemical processes, because his low kinetics decreases system efficiency. The main progresses in the cathodic side have been related to the development and improvement of activity and stability. In this way, non precious material has been studied, in the last years. Cobalt oxides have been reported to exhibit good performance for ORR. However, cobalt bimetallic can be more eficient catalysts for ORR, especially for its bifunctional function. Some Ni-based electrocatalysts have shown relevant good results for ORR in four-electron pathway. Song et al. Showed, for example, that Ni addition into Ag-based electrocatalysts for ORR decreases the ORR overpotential, while an increasing in the limiting current density is observed. In this way, a bimetallic CoNi/ C was produced to be used as a cathode in alkaline fuel cell.
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.
Desenvolvimento de eletrocatalisadores de PdM (M= Ni, Cu, Ag) para reação de redução de oxigênio em meio básico na ausência e presença de álcool
2015 - ISIDORO, ROBERTA A.
Eletrocatalisadores baseados em Pd/C, PdCu/C, PdNi/C e PdAg/C foram produzidos pelo método de micro-ondas para serem utilizados como cátodo na célula a combustível alcalina na ausência e presença de álcool. Este método se mostrou bastante efetivo para a produção dos materiais, uma vez que as partículas apresentaram boa dispersão no suporte de carbono e produziram eletrocatalisadores com tamanho de partícula em torno de 3,5 nm, de acordo com as análises de DRX e MET. A partir das voltametrias cíclicas observa-se que para os eletrocatalisadores de PdCu/C e PdNi/C quanto maior a quantidade de Cu ou Ni, respectivamente, maior a área ativa do material estudado. Análises de disco anel rotatório foram realizadas nos eletrocatalisadores demonstrando que, independente da composição estudada, a quantidade produzida de peróxido foi de no máximo 4%. Estes dados corroboram com as inclinação das retas nas análises de Koutecky-Levich, uma vez que em ambos os casos a RRO ocorre via 4 elétrons. Análises de estabilidade dos materiais demonstraram que todos eles mantiveram ou melhoraram seu desempenho diante da RRO, quando se compara os dados obtidos antes e depois de 1000 ciclos voltamétricos. Testes de tolerância ao metanol e etanol foram realizados em meia célula com todas as composições de eletrocatalisadores produzidos. Na presença tanto de metanol quanto de etanol as composições atômica de 50:50, para todos os materiais estudados, foram as que demonstraram menor influência da presença do álcool durante a varredura linear da RRO. Nas medidas realizadas em célula unitária, com relação à tolerância ao metanol durante a RRO, o eletrocatalisador que demonstrou melhor desempenho foi o PdAg/C 70:30 enquanto que na presença de etanol o eletrocatalisador que demonstrou melhor desempenho foi o PdNi/C 70:30.
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.
Estudo teórico-experimental de otimização de componentes de células a combustível do tipo PEM de alta eficiência
2014 - ISIDORO, ROBERTA A.; PAULINO, ANDRE L.R.; ROBALINHO, ERIC; CUNHA, EDGAR F.; PASSOS, RAIMUNDO R.; SANTIAGO, ELISABETE I.
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.