Chemistry

The cyclic oxidation behavior of an experimental stainless ferritic steel, without molybdenum and with copper-aluminum-titanium-lanthanum additions, developed for solid oxide fuel cell applications, was evaluated and compared with the oxidation behavior of commercial austenitic and ferritic stainless steels. For the cyclic oxidation tests, the steel samples were tested at temperatures ranging from 600 to 800°C. The experimental ferritic stainless steel showed the highest cyclic oxidation behavior among the studied steels at 700°C and 800°C, presenting a parabolic and logarithmic kinetics, respectively.

The formation of insulating phases at the interface between cathode and electrolyte materials during solid oxide fuel cell (SOFC) operation leads to deleterious effects on SOFC properties. We report in situ impedance spectroscopy measurements of the degradation process of porous La 0.65 Sr 0.35 MnO 3 /Zr 0.84 Y 0.16 O 1.92 electrodes submitted to annealing temperatures above normal SOFC operating temperature, which is around 1173 K, simulating longterm SOFC operation. To measure the remaining effects after high-temperature annealing, impedance diagrams were plotted during the entire heating process up to the annealing temperatures, and during the complete cooling process. These diagrams were also plotted during the aging periods to follow the overall degradation. It was possible to detect and quantify electrical and electrochemical degradations, which are related to the formation of insulating phases at the electrode/electrolyte interface. Samples were annealed for about 200 h in air at temperatures between 1373 and 1673 K. Scanning electron microscopy and energy-dispersive X-ray spectrometry were also used to detect microstructural changes at the electrode.

Symmetrical cells have been prepared by depositing suspensions with different active powder concentrations (50% and 60% by weight respectively) of lanthanum strontium cobalt iron oxide (La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3−ı ) on identical yttria stabilized zirconia pellets (LSCF/YSZ/LSCF). Their impedance characteristics are compared to that of a symmetrical cell with platinum electrodes deposited on a similar zirconia pellet (Pt/YSZ/Pt). The LSCF cells show different values of the electrolyte resistance. Referring to the electrolyte resistance obtained with the Pt cell and assuming that this value corresponds to almost perfect electrode/electrolyte contacts, it is possible to estimate the Effective Conducting Area (ECA) of the electrodes. The use of the ECA parameter allows a better comparison of the electrode polarizations.

LSCF Oxidative processes a b s t r a c t In this paper, oxygen evolution reaction (OER) mechanism in La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 was investigated in KOH solution by electrochemical impedance spectroscopy (EIS) and voltammetric measurements. The Tafel slopes and reaction orders evaluated in this paper are consistent with the B. O'Grady's Path for oxygen evolution on oxides. The activation energy for OER in La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 was 28.3 kJ mol À1 . The obtained apparent porosity of La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 electrode is 48% and the roughness factor is around 1.6 Â 10 4 . The polarization resistance of La 0.6 Sr 0.4 Co 0.8 Fe 0.2 O 3 is much low compared with other similar

The supercapacitive behavior of the metallic cobalt recycled from Li-ion batteries has been studied in this work. The reversibility of both redox process (Co II /Co III ) and (Co III /Co IV ) in KOH 6 mol L -1 is very high and promising for capacitive applications in electrochemical devices. The specific capacitances calculated from cyclic voltammetry and electrochemical impedance spectroscopy show a good agreement, giving the value of 625 Fg -1 . The electrode morphology presents a high porosity, thus an electrical equivalent circuit composed of two parallel resistance and capacitance elements in series was proposed. The specific capacitance values calculated from charge/discharge curves at 0.23 and 2.3 mA/cm 2 are 601 and 384 Fg -1 , respectively. Thereby, it was observed that metallic cobalt recycled from ion-Li batteries is compatible with other supercapacitive materials. This shows that cobalt recycling from Li-ion batteries is economically and environmentally viable for application in supercapacitor devices.

Recebido em 7/8/08; aceito em 16/1/09; publicado na web em 11/5/09 ASSEMBLY AND ELECTRICAL CHARACTERIZATION OF SOLID OXIDE FUEL CELL STACKS. This paper is focused on a review of the design features and the electrochemistry characterization of anode-supported planar SOFC. Studies and results of metallic alloy interconnectors and recovery for protection against corrosion and for contact layer are showed. Moreover a discussion of examples of measurements of impedance spectrometry, according to the literature and our experimental results are made. For the anode supported fuel cells the power density varies from 0.1 to 0.5 Wcm 2 , according to results in the literature (showed in this paper). For electrolyte supported fuel cell the power density can be 10 Wcm -2 for high temperatures. An English-Portuguese glossary of most used terms in SOFC stack is given for greater clarity and to introduce new terms to the reader.

Electrochemical cells formed by the interface between dense and porous lanthanum strontium manganate (LSM) and yttria stabilized zirconia (YSZ) were submitted to annealing temperatures varying from 1373 K to 1673K for 200h and studied by Impedance Spectroscopy (IS) in order to investigate how the high annealing temperature can modify the contact between LSM/YSZ and to which extension these changes influence the electrical behavior of dense and porous LSM electrodes before and after the formation of insulating phases. Up to 1473K the annealing process did not lead to substantial electrical behavior modifications at the LSM/YSZ interfaces for both porous and dense electrodes. IS measurements show two capacitive semicircles, the best fitting of impedance data brings to an equivalent circuit constituted by a serial combination of the electrolyte resistance and two parallel combinations of a resistance and a constant phase element, CPE. The higher frequency semicircles, HF, were attributed to the diffusion of oxide ions from the interface LSM/YSZ to the oxide ion vacancies located at the electrolyte surface. The semicircle at lower frequency, LF, will be ascribed to the oxygen species adsorption and diffusion in the LSM. At 1473K the only changes recorded are related with the sinterization process of the porous electrodes. Over of 1473K, the resistance contributions increased largely, especially for porous electrodes, and one additional semicircle was observed. This semicircle was associated to the oxygen diffusion process at the new insulating phases formed from YSZ and LSM solid state reactions. Porous and dense electrodes exhibited different rates for the degradation process. The porous electrode degraded faster than the dense one, probably because of the morphological effects as grain growth and their coalescence during annealing at higher temperatures.

A modelagem computacional contribui para o projeto, o dimensionamento e, também, para a avaliação do desempenho de pilhas a combustível de óxido sólido. No entanto, essa modelagem é complexa devido a grande quantidade de fenômenos físicos envolvidos. Além dos fenômenos físicos, as dimensões presentes dificultam a validação dos resultados. Neste trabalho, os canais de um interconector adjacente a um anodo foram modelados visando avaliar o escoamento nesse sistema. A validação dos procedimentos e das considerações foi feita de maneira indireta. O escoamento no interconector foi avaliado através das equações de Navier-Stokes e, no anodo, foi utilizada a Lei de Darcy. A técnica de volumes finitos foi empregada para a solução das equações. Foram utilizados valores típicos de permeabilidade, enquanto viscosidade e densidade foram determinadas numericamente, considerando a mistura de hidrogênio e água. Foi considerado regime permanente e isotropia em relação a todas as propriedades físicas determinadas a várias temperaturas. Foram analisadas as influências no escoamento da razão entre porosidade do anodo e viscosidade da mistura H 2 e H 2 O; da densidade e; da temperatura. Um estudo de como a densidade da malha afeta os resultados também foi realizado. Foi possível notar que, quando a mistura hidrogênio/água penetra no meio poroso, o escoamento sofre uma redução de velocidade, em relação ao valor médio aplicado na entrada. Já a pressão, nessa situação, não apresenta redução significativa.

O grande desafio para se melhorar o desenvolvimento de pilhas a combustível de óxido sólido (PACOS) é diminuir as resistências de polarização ôhmica e de polarização de concentração, sobretudo no catodo. Uma alternativa efetiva é a introdução de uma camada catódica funcional entre o eletrólito e o catodo convencional. Esta camada funcional é um compósito constituído pelos materiais de eletrólito e catodo que neste caso são a zircônia estabilizada com ítria (ZEI) e a manganita de lantânio e estrôncio (MSL). Esta camada melhora o contato entre o catodo e o eletrólito diminuindo a resistência ôhmica de polarização de concentração devido ao aumento do número de pontos de contato triplo (PCT) no volume do material.

A atividade eletroquímica do compósito cerâmico metálico (cermet) Ni/Zr 0,85 Y 0,15 O 0,93 (Ni/ZEI) utilizado como ânodo em pilhas a combustível de óxido sólido (PaCOS), é controlada pela condutividade intrínseca das fases presentes e pelos caminhos disponíveis para a condução elétrica e para a difusão do gás combustível. Essas propriedades são fortemente influenciadas por parâmetros microestruturais, tais como distribuição espacial das fases, forma e tamanho médio das partículas que constituem o cermet.

In this paper, a new anode for oxygen evolution reaction was developed from recycling of spent Li-ion cathode. After heating at 400 C for 24 h, the spent cathode has LiCoO 2 and Co 3 O 4 in its composition. This new material was mixed with graphite and conformed in tablet for application as anode in oxygen evolution reaction in alkaline solution (NaOH 6.0 mol L À1 ). The concentrations of cathode in this mixture were 0, 10, 20 and 50% in mass.

Background: Dengue is a major public health problem worldwide, especially in the tropical and subtropical regions of the world. Infection with a single Dengue virus (DENV) serotype causes a mild, self-limiting febrile illness called dengue fever. However, a subset of patients experiencing secondary infection with a different serotype progresses to the severe form of the disease, dengue hemorrhagic fever/dengue shock syndrome. Currently, there are no licensed vaccines or antiviral drugs to prevent or treat dengue infections. Biodegradable nanoparticles coated with proteins represent a promising method for in vivo delivery of vaccines. Findings: Here, we used a murine model to evaluate the IgG production after administration of inactivated DENV corresponding to all four serotypes adsorbed to bovine serum albumin nanoparticles. This formulation induced a production of anti-DENV IgG antibodies (p < 0.001). However, plaque reduction neutralization assays with the four DENV serotypes revealed that these antibodies have no neutralizing activity in the dilutions tested. Conclusions: Our results show that while the nanoparticle system induces humoral responses against DENV, further investigation with different DENV antigens will be required to improve immunogenicity, epitope specicity, and functional activity to make this platform a viable option for DENV vaccines.