Showing papers by "Enrique Ruiz-Trejo published in 2017"

Guidelines for the Rational Design and Engineering of 3D Manufactured Solid Oxide Fuel Cell Composite Electrodes

Abstract: The growth of 3D printing has opened the scope for designing microstructures for solid oxide fuel cells (SOFCs) with improved power density and lifetime. This technique can introduce structural modifications at a scale larger than particle size but smaller than cell size, such as by inserting electrolyte pillars of ∼5–100 μm. This study sets the minimum requirements for the rational design of 3D printed electrodes based on an electrochemical model and analytical solutions for functional layers with negligible electronic resistance and no mixed conduction. Results show that this structural modification enhances the power density when the ratio keff between effective conductivity and bulk conductivity of the ionic phase is smaller than 0.5. The maximum performance improvement is predicted as a function of keff. A design study on a wide range of pillar shapes indicates that improvements are achieved by any structural modification which provides ionic conduction up to a characteristic thickness ∼10–40 μm without removing active volume at the electrolyte interface. The best performance is reached for thin (<∼2 μm) and long (>∼80 μm) pillars when the composite electrode is optimised for maximum three-phase boundary density, pointing toward the design of scaffolds with well-defined geometry and fractal structures. © The Author(s) 2016. Published by ECS. This is an open access article distributed under the terms of the Creative Commons Attribution 4.0 License (CC BY, http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse of the work in any medium, provided the original work is properly cited. [DOI: 10.1149/2.0501702jes] All rights reserved.

Microstructural Degradation: Mechanisms, Quantification, Modeling and Design Strategies to Enhance the Durability of Solid Oxide Fuel Cell Electrodes

Abstract: Electrode microstructure is one of the main factors determining the performance and durability of solid oxide fuel cells (SOFCs). The degradation is intimately linked to the microstructure, which in turn depends upon manufacturing and operation conditions. In this chapter we discuss the main causes for degradation of electrodes, concentrating mainly on the anode and present the techniques—both typical and state-of-the-art to follow these changes. We emphasize the need to quantitatively link the microstructural properties (e.g., triple-phase boundaries, porosity, and tortuosity) with the electrochemical responses measured and, most importantly, to link the change in microstructure to the performance degradation via suitable models. The knowledge gained must then be used to design new electrodes that can extend the lifetime of SOFCs once the critical parameters have been identified.

New Method for the Deposition of Nickel Oxide in Porous Scaffolds for Electrodes in Solid Oxide Fuel Cells and Electrolyzers

Abstract: A simple chemical bath deposition is used to coat a complex porous ceramic scaffold with a conformal Ni layer. The resulting composite is used as a solid oxide fuel cell electrode, and its electrochemical response is measured in humidified hydrogen. X-ray tomography is used to determine the microstructural characteristics of the uncoated and Ni-coated porous structure, which include the surface area to total volume, the radial pore size, and the size of the necks between the pores.

Microstructural and Electrochemical Characterisation of Degradation in Nickel Impregnated Scandia-Stabilised Zirconia Electrode during Isothermal Annealing

Abstract: In this study, we examine the degradation of nickel impregnated scandia-stabilised zirconia (ScSZ) electrode in wet hydrogen at a working temperature of SOFCs. Continuous van der Pauw measurement was carried out when the electrode was aged at 650 oC in an atmosphere with 5 vol% hydrogen and 95 vol% nitrogen. A fall in sheet conductivity was found in the electrode during ageing within 1000 min. Electrochemical impedance spectra were collected at a constant time intervals during isothermal annealing at 650 oC, 800 oC and 950 oC for the impregnated electrode, at open circuit. Three resistance contributions were decoupled by equivalent circuit fitting, i.e. the ohmic resistance, the anodic reaction resistance, and the gas diffusion resistance. Secondary electron images of electrodes before and after ageing showed an increase in nickel particle size and a decrease in the number of particles, providing microstructural evidence of coarsening. Nickel coarsening was identified as the main mechanism of degradation for the electrode in wet hydrogen.