A distributed charge transfer model for IT-SOFCs based on ceria electrolytes

A distributed charge transfer model for IT-SOFCs with MIEC electrolyte and composite electrodes is developed. A physically-based description of the electronic leakage current in the electrolyte is included, together with mass and charge conservation equations. The model is applied to simulate experimental polarization curves and impedance spectra collected on IT-SOFCs consisting of SDC electrolytes, Cu-Pd-CZ80 infiltrated anodes and LSCF/GDC composite cathodes. Hydrogen electro-oxidation experiments are examined (H2/N2humidified mixtures, 700â\u97¦C, 30â\u80\u93100% H2molar fraction). A significant increase of the ohmic resistance measured in the impedance spectra is revealed at decreasing the H2partial pressure or increasing the voltage (from 0.71 cm2at 100% H2to 0.81 cm2at 30% H2). Good agreement between the calculated and experimental polarization and EIS curves is achieved by fitting the exchange current density and the capacitance of each electrode. Model and theoretical analyses allow to rationalize the observed shift of the ohmic resistance, highlighting the key-role played by the electronic leakage current. Overall, the model is able to capture significant kinetic features of IT-SOFCs, and allows to gain insight into relevant parameters for the optimal design of the cell (electrochemically active thickness, current and potential distribution, mass diffusion gradients)

Effect of synthetic route on performance of La0.8Sr1.2Fe0.9Cu0.1O4±δ electrodes for symmetric solid oxides fuel cells

The solid oxide La0.8Sr1.2Fe0.9Cu0.1O4±δ of interest as electrode for Symmetric Solid Oxide Fuel Cells (SSOFCs) has been prepared via three different synthetic methods: solid-state reaction (SSR), melt citrate route (MC) and co-precipitation (CoP). In order to determine advantages and drawbacks of each synthesis, the materials have been characterized by X-Ray Powder Diffraction (XRD) and Scanning Electron Microscopy (SEM) analysis. Phase purity, structural and morphological characteristics of the powders have been determined. Wet chemical methods (CIT and COP) have the advantage over SSR synthesis of yielding small-sized powders (â\u88¼1mu;m); moreover, melt citrate route allows lowering the preparation temperature down to 1000 °C. Electrochemical characterization was performed by Electrochemical Impedance Spectroscopy (EIS) in air in an electrolyte supported symmetric cells configuration. Preliminary results allow to draw some conclusions on the relation between the structural and microstructural characteristics of the powders and the electrochemical performance

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

Balance between model detail and experimental information in steam methane reforming over a Ni/MgO-SiO2 catalyst

The optimization and full understanding of chemical reactions is aided by the construction of an adequate kinetic model. The development of such a kinetic model remains a challenging task. To tackle this challenge in the most efficient way, an iterative, systematic methodology, originally demonstrated for n-hexane hydroisomerization, is now extended aiming at finding the balance between the envisaged model detail and available information, often originating from time-consuming and expensive experiments. Steam methane reforming on the Ni/MgO-SiO2 case study is used for this purpose, that is, the construction of a kinetic model that embeds a maximum amount of information contained in the dataset. The kinetic model is expanded stepwise from a power law model over a model with reactant adsorption toward a Langmuir-Hinshelwood-Hougen-Watson model. The performance of the initially underparameterized model improved significantly by adding reactant adsorption, yet including product adsorption led to overparameterization rather than enhanced model performance

Model analysis of atmospheric non-thermal plasma for methane abatement in a gas phase dielectric barrier discharge reactor

A physical model of a non-thermal plasma reactor for the abatement of CH4 emissions is presented. The model includes mass balances for neutral, charged and radical species, the enthalpy balance for the gas phase and specific equations for electron temperature and density. The kinetic scheme of CH4 abatement couples the GRI-Mech set of radical reactions (325 steps) with ten sets of plasma reactions (108 steps), which comprise elastic collisions, direct ionization, dissociative ionization, excitation and attachment reactions. The model is validated based on literature results that explore the effects of Specific Input Energy, gas temperature and H2O addition. The results highlight that dissociative electron-impact reactions produce chemically active OH and O radicals, which boost CH4 conversion, making H2O a key abatement promoter in the plasma process. The heating effect induced by electron collisions is relevant, suggesting that an accurate control of thermal insulation is crucial to characterize the reactor performance

Characterization and Testing of Exsolution-Based Solid Oxide Cells for Reversible Operations in CO2 Electrolysis

Reversible solid oxide cells (rSOCs) are promising electrochemical devices, able to work both in energy storage mode as solid oxide electrolyzes (SOECs), and in power generation mode as solid oxide fuel cells (SOFCs). rSOCs dedicated to high-temperature co-electrolysis of CO2/H2O mixtures are of interest since they could foster the utilization and consequent reduction of CO2 gas emissions while converting it and H2O into valuable fuels (i.e. syngas and H2). However, operation under CO2-rich feeds requires alternatives to the state-of-the-art Ni-Yttria-stabilized-zirconia (Ni-YSZ) cermet fuel electrode in view of its low coking and redox resistance. Perovskites with mixed ionic and electronic conductivity are major alternatives, especially when the functionality of their active surface is enhanced via metal nanoparticle exsolution. This work focuses on the investigation of the electrocatalytic properties of the SrTi0.3Fe0.7O3 (STF), and exsolution Sr0.95(Ti0.3Fe0.63Ni0.07)O3 (STF-Ni) perovskite-based fuel electrodes together with Ni-YSZ while operating with CO2-rich mixtures both in the short and long term

CFD Analysis of the Channel Shape Effect in Monolith Catalysts for the CH 4

Catalysts monoliths with circular and square ducts are theoretically analyzed in detail as reactor configurations for the adiabatic CH4 partial oxidation on Rh for short-contact-times hydrogen production. By the means of CFD coupled with a detailed microkinetic description of the surface reactivity, it was found that the different transport properties of the investigated configurations primarily affect the thermal behavior of the reactor. O2 consumption is fully external mass transfer limited, and thus, local variations in mass transport properties are responsible of the differences in surface temperature