Modification of LSF-YSZ Composite Cathodes by Atomic Layer Deposition

composite, Solid-Oxide-Fuel-Cell (SOFC) electrodes of La0.8Sr0.2FeO3 (LSF) and yttria-stabilized zirconia (YSZ) were prepared by infiltration methods and then modified by Atomic Layer Deposition (ALD) of ZrO2, La2O3, Fe2O3, or La2O3-Fe2O3 codeposited films of different thicknesses to determine the effect of surface composition on cathode performance. Film growth rates for ALD performed using vacuum procedures at 573 K for Fe2O3 and 523 K for ZrO2 and La2O3 were determined to be 0.024 nm ZrO2/cycle, 0.019 nm La2O3/cycle, and 0.018 nm Fe2O3/cycle. For ZrO2 and Fe2O3, impedance spectra on symmetric cells at 873 K indicated that polarization resistances increased with coverage in a manner suggesting simple blocking of O2 adsorption sites. With La2O3, the polarization resistance decreased with small numbers of ALD cycles before again increasing at higher coverages. When La2O3 and Fe2O3 were co-deposited, the polarization resistances remained low at high film coverages, implying that O2 adsorption sites were formed on the co-deposited films. The implications fo these results for future SOFC electrode development are discussed

MÉTODOS DE INDEXAÇÃO DE INDICADORES NA AVALIAÇÃO DA QUALIDADE DO SOLO EM RELAÇÃO À EROSÃO HÍDRICA

A avaliação da qualidade dos solos agrícolas é importante para definição e adoção de práticas de manejo que garantam a sustentabilidade socioeconômica e ambiental. Os métodos de indexação dos indicadores de qualidade denominados Índice de Qualidade Integrado (IQI) e Índice de Qualidade Nemoro (IQN) foram utilizados neste estudo para avaliar a qualidade de solo em áreas experimentais de plantio de eucalipto. A seleção dos indicadores foi feita a partir de nove indicadores de qualidade do solo: diâmetro médio geométrico, permeabilidade à água, matéria orgânica, macro e microporosidade, volume total de poros, densidade do solo, resistência à penetração e índice de floculação, que estão relacionados à erosão hídrica. Os tratamentos constituíram de eucalipto plantado em nível, com e sem a manutenção dos resíduos, em desnível e solo descoberto, em dois biomas distintos, cujas vegetações nativas são Cerrado e Floresta. Os índices de qualidade do solo (IQS) apresentaram alta correlação com a erosão hídrica. Entre os sistemas manejados, o Eucalipto com manutenção do resíduo evidenciou valores mais elevados em ambos os índices, ressaltando-se a importância da cobertura vegetal e manutenção da matéria orgânica para conservação do solo e da água em sistemas florestais. Os IQS demonstraram alto coeficiente de correlação inversa com as perdas de solo e água. Em locais com as maiores taxas de erosão hídrica manifestaram também os menores valores de IQI e IQN. Assim, os índices testados permitiram avaliar com eficácia os efeitos dos manejos adotados sobre a qualidade do solo em relação à erosão hídrica

Distributed-charge transfer model analysis of SDC-based IT-SOFCs for the electrochemical oxidation of syngas and biogas

Aim of this work is the development of a distributed charge-transfer numeric model for intermediate temperature solid oxide fuel cells (IT-SOFCs) with composite electrodes. The model describes the leakage current inside a mixed ionic electronic conducting (MIEC) electrolyte. The reaction interface is extended along the whole length of the electrodes and a one-dimensional description of charge transfer phenomena is entailed. The profiles of the ionic and the electronic current density, as well as the profiles of the ionic and the electronic potentials are described along the whole length of the cell. The model is applied to analyze the experimental results of IT-SOFCs based on Samarium doped Ceria (SDC) electrolytes, Cu-Pd-CZ80 anodes and LSCF cathodes. Hydrogen electro-oxidation experiments are examined first, then the analysis is extended to the simulation of OCV data collected when feeding biogas mixtures to the anode

Kinetic investigation of the oxygen reduction reaction on LSCF-GDC composite cathodes for use in IT-SOFCs

A kinetic investigation of the Oxygen Reduction Reaction (ORR) was performed on LSCF-GDC composites cathodes spanning a wide range of operating conditions. EIS tests were carried out on symmetric cells between 700°C and 550°C under OCV conditions, with O2/N2 mixtures at varying the O2 molar fraction (5-100%). A dynamic, one-dimensional and physically-based model of the LSCF-GDC cathode was applied to rationalize the experimental results. The model simulates the spectra by solving mass and charge conservation equations, including terms for gas diffusion inside the electrode pores and solid state transport of oxygen vacancies inside the bulk of LSCF and GDC. A detailed kinetic scheme was chosen to describe the ORR mechanism, which took into account steps for adsorption and desorption, first and second electronation at the gas/electrode interface, interfacial and lattice ion transfer. An advanced numerical approach allowed to cut the computational times. Novel insights supporting the 2PB reaction pathway were provided by means of a sensitivity analysis on the kinetic parameters

Electrodilatometric analysis under applied force: A powerful tool for electrode investigation

A new equipment for in situ electrochemical dilatometry is designed and validated by studying the volumetric changes of a model electrode. The contactless measurement system permit to not influence the dilation of the sample during the tests. In addition, different forces can be applied in a selected range. Graphite is selected as model electrode and electrochemical tests in different electrolytes are carried out under different applied forces. The results of the electrodilatometric tests on graphite in EC:DMC- and in PC-based electrolyte reveal not only lithium insertion/deinsertion process, but also the presence of simultaneous phenomena like solvent evaporation, SEI formation and gas evolution. The latter has been detected by applying different forces that affect the gas uptake and release from porous separator. Controlled hydrogen evolution experiments were carried out at different applied forces in order to assess the gassing detection ability of the dilatometer. We demonstrate that with this new equipment it is possible, from thickness variation, to collect information on processes of different nature. Specifically, different applied forces emphasized gas evolution, which is a worth studying phenomenon for increasing battery safety

Experimental and model analysis of the co-oxidative behavior of syngas feed in an Intermediate Temperature Solid Oxide Fuel Cell

By means of model analysis, we show that, in the presence of syngas, the electro-oxidation of H2 and that of CO occur in parallel and contemporarily on Samaria-doped Ceria (Sm0.2Ce0.8O1.9, SDC) Intermediate Temperature Solid Oxide Fuel Cells (IT-SOFCs). The activation of a co-oxidative route is a most distinguishing feature of Ce-based cells, compared to traditional SOFCs. SDC electrolyte supported IT-SOFCs with Cu-Pd-CZ80 composite anodes and LSCF cathodes were tested under a wide range of operating conditions. Polarization and EIS measurements were collected at 600 \ub0C and 650 \ub0C with syngas mixtures (2.3-0.4H2/CO ratio), H2/N2 mixtures (from 97 to 30% H2 v/v) and CO/CO2 mixtures (from 97 to 50% CO v/v). A 1D, dynamic and heterogeneous model of the cell was applied to analyze the polarization and the EIS curves. The kinetics of the reactions of H2 electro-oxidation, CO electro-oxidation and O2 reduction were individually investigated and global power law rates were derived. The syngas experiments were simulated on a fully predictive basis and no parameter adjustment, confirming that the polarization behavior could be best reproduced exclusively by assuming the presence of the co-oxidative route. The IT-SOFCs were also exposed to biogas mixtures, revealing that the dry-reforming reaction was active. \ua9 2015 Elsevier B.V. All rights reserved

Functional separators for the batteries of the future

Lithium/sulfur batteries are one of the most promising technologies for the next-generation batteries. However, this technology suffers from several problems mainly related to the instability of metallic lithium and to the polysulfides (PS) shuttle. An approach to address such issues is the design of new separators or the modification of existing commercial ones. The use of hybrid membranes is here proposed to improve the performance of Li metal anode and sulfur cathode. Composite separators are obtained by electrospinning or drop-casting a polymer solution of polyvinylidenefluoride (PVdF) containing graphene oxide (GO) on a polyolefin commercial Celgard 2300 separator. This is the first time that a thin layer of electrospun PVdF/GO composite is applied to a polyolefin separator for the use in Li metal-based batteries. We demonstrate that electrospinning is an effective method to obtain a thin polymer layer of PVdF/GO. The electrospun layer improves the wettability of the separator; it is beneficial to the growth of \u201csoft\u201d dendrite on Li anode and has a positive effect on the PS shuttle process. The casted layer featuring a higher GO content is also effective in increasing the separator wettability, although with a minor effect on Li interphase