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

Preparation, Characterization, and Kinetic Testing of Infiltrated LSF-YSZ Electrodes for Symmetric Solid Oxide Cells

In this work, symmetric electrolyte-supported YSZ (yttria-stabilized zirconia) cells infiltrated with LSF (La0.8Sr0.2FeO3O3-δ) were prepared, characterized, and tested in the oxygen reduction reaction (ORR). The fabrication procedure of the cells was optimized with respect to the formulation of the electrolyte and electrode slips. Aqueous solutions of nitrates were used for the LSF-YSZ electrodes, which were morphologically characterized prior and after infiltration. The effects of calcination temperature (between 700 and 1050 °C) and precursors load (between 10% and 50% w/w) on the ORR activity were investigated. Electrochemical impedance spectroscopy (EIS) experiments were performed between 650 and 750 °C, with air and varying the O2 partial pressure from 5% to 100%. The minimum polarization resistance was measured after calcination at 750 °C, while LSF loads between 20% and 40% maximized the performance. Equivalent circuit analysis of the EIS results suggested that the surface reactivity at the LSF/gas interface is rate-determining

A multistep model for the kinetic analysis of the impedance spectra of a novel mixed ionic and electronic conducting cathode

A one-dimensional, heterogeneous and dynamic model is applied to kinetically analyze impedance experiments performed on a novel NdBa0.9Co2O5.6 (NBC) MIEC cathode. The model simulates the spectra in the time domain by accounting for the gas diffusion inside the electrode pores, and for the solid state diffusion of oxygen vacancies inside the bulk of the cathodic material. A detailed kinetic scheme is applied to describe the oxygen reduction mechanism, which includes steps for adsorption and desorption, first and second electronation at the gas/electrode interface, and ion transfer at the electrode/electrolyte interface. The kinetic investigation is based on impedance spectra collected on symmetric NBC/GDC/NBC cells, at open circuit voltage, between 550 and 700°C, and 5–100% O2 molar fraction. The vacancies diffusion coefficient and the kinetic parameters of the reaction steps are fitted to describe the data. At the highest temperatures, a sensitivity analysis reveals that the rate determining step is the first electronation of the oxygen adatom, while the second electronation and the interfacial ion transport are kinetically irrelevant. Overall, the model allows to individuate the key parameters for capturing the kinetics of a MIEC cathode

A multi-scale modelling approach and experimental calibration applied to commercial SOFCs

The present study aims at laying the theoretical basis for a multiscale modelling approach applicable to state-of-the-art commercial SOFCs. The proposed multi-scale model is built with the main purpose to understand how micro-scale characteristics of the PEN structure and the thermo-chemical and electrochemical phenomena, which occur in the electrode and electrolyte assembly, may affect the overall performance of a complete cell and ultimately of the stack. This study presents the integration of two-dimensional finite volume models: a 1D micro-scale model and a 1D (or 2D) macroscale (channel/cell) model. The analysis evidences how stack optimisation should focus on the micro-structure characteristics, which should also change along the reactant channels (x direction) in relation to the local variation of temperature and composition. The model therefore lays the basis for cell local optimisation and design-led techniques required for performance enhancement

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