3D Microstructure Effects in Ni-YSZ Anodes: Prediction of Effective Transport Properties and Optimization of Redox Stability

Materials

Omar M. Pecho²  Ole Stenzel²  Boris Iwanschitz³  Philippe Gasser⁵  Matthias Neumann⁴  Volker Schmidt⁴  Michel Prestat²  Thomas Hocker²  Robert J. Flatt¹  Lorenz Holzer² 

[1] Institute for Building Materials, ETH Zurich, Zurich 8093, Switzerland; E-Mail:;Institute of Computational Physics, Zurich University of Applied Sciences, Winterthur 8400, Switzerland; E-Mails:;Hexis SA, Winterthur 8404, Switzerland; E-Mail:;Institute of Stochastics, Ulm University, Ulm 89069, Germany; E-Mails:;Scientific Center for Optical and Electron Microcopy (ScopeM), ETH Zurich, Zurich 8093, Switzerland; E-Mail:

关键词: cermet;    degradation;    microstructure;    tomography;    conductivity;    solid oxide fuel cells;    Ni-YSZ;    redox cycling;   

DOI  :  10.3390/ma8095265

来源: mdpi

【 摘 要 】

This study investigates the influence of microstructure on the effective ionic and electrical conductivities of Ni-YSZ (yttria-stabilized zirconia) anodes. Fine, medium, and coarse microstructures are exposed to redox cycling at 950 °C. FIB (focused ion beam)-tomography and image analysis are used to quantify the effective (connected) volume fraction (Φ_eff), constriction factor (β), and tortuosity (τ). The effective conductivity (σ_eff) is described as the product of intrinsic conductivity (σ₀) and the so-called microstructure-factor (M): σ_eff = σ₀ × M. Two different methods are used to evaluate the M-factor: (1) by prediction using a recently established relationship, M_pred = εβ^0.36/τ^5.17, and (2) by numerical simulation that provides conductivity, from which the simulated M-factor can be deduced (M_sim). Both methods give complementary and consistent information about the effective transport properties and the redox degradation mechanism. The initial microstructure has a strong influence on effective conductivities and their degradation. Finer anodes have higher initial conductivities but undergo more intensive Ni coarsening. Coarser anodes have a more stable Ni phase but exhibit lower YSZ stability due to lower sintering activity. Consequently, in order to improve redox stability, it is proposed to use mixtures of fine and coarse powders in different proportions for functional anode and current collector layers.

【 授权许可】

CC BY   
© 2015 by the authors; licensee MDPI, Basel, Switzerland.