Journal of Power Sources 163 (2007) 900–906 Fracture strength of micro-tubular solid oxide fuel cell anode in redox cycling experiments Jakub Pusz a,∗ , Alevtina Smirnova a , Alidad Mohammadi a , Nigel M. Sammes a,b a Department of Chemical, Materials, and Biomolecular Engineering, University of Connecticut, 44 Weaver Road, Storrs, CT 06269, USA b Department of Mechanical Engineering, University of Connecticut, 44 Weaver Road, Storrs, CT 06269, USA Received 8 August 2006; received in revised form 27 September 2006; accepted 29 September 2006 Available online 17 November 2006 Abstract The maximum fracture strength of Ni/8YSZ anodes exposed to several redox cycles is compared. The anodes were fabricated using fine and coarse particle size powders. Fine-structured powders show a 77% increase in mechanical strength after exposure to three redox cycles. The coarse-structured material did not produce similar results and redox cycling resulted in gradual decrease in the mechanical stability of the supports. The impact of redox cycling on the microstructure was evaluated using SEM. Fine-structured anodes tend to agglomerate leading to decreased porosity. Coarse anodes did not show any significant changes in microstructure while exposed to redox cycling. The electrochemical performance evaluated under load conditions, and after the first redox cycle, indicates a 40% improvement for the cell fabricated using a fine-structured anode powder. The increase in performance is believed to be due to better adhesion between the anode material and the Ni current collector. The cell fabricated using a coarse-structured anode powder did not recover after the redox cycle. © 2006 Elsevier B.V. All rights reserved. Keywords: SOFC; Redox; Anode; Strength; Morphology; Particle size 1. Introduction Solid oxide fuel cells (SOFC) fabricated using a standard nickel–cermet anode, presents good catalytic activity towards the oxidation of hydrogen and hydrocarbon fuels [1–7]. In order to improve long-term stability of the anode, nickel is typically mixed with yttria stabilized zirconia. A mixture of coarse and fine particles are traditionally used whereby coarse particles are usually 25 m or larger [8], and are responsible for matching the thermal expansion coefficient of the YSZ electrolyte layer. The fine particles are approximately 0.5 m in size and prevent nickel from agglomeration and co-sintering. Such a composition of anode substrate prevents delamination and cracking of the electrolyte layer due to the thermal expansion mismatch as well as keeping the desired anode porosity. This approach improves long-term mechanical stability of Ni/YSZ-based materials oper- ated under a reducing environment. Exposure of nickel–cermet anode to reoxidation, however, results in change of the physi- ∗ Corresponding author. Tel.: +1 860 486 5407; fax: +1 860 486 8378. E-mail address: jpusz@engr.uconn.edu (J. Pusz). cal and mechanical properties that potentially leads to failure of the cell. Work has shown that redox cycling results in volumetric changes of the cermet anode [9]. The studies show that the kinetics of Ni oxidation is dependent upon powder processing procedures, especially surface preparation, grain/particle size, and impurity levels [9–12]. The fine-structured anodes expe- rience no change in volume upon reduction; yet, a 2–2.5% increase in volume occurs during reoxidation [9]. Such an expansion could potentially result in an increase of the inter- nal stresses of the nickel crystal structure which could affect the integrity of the cell. Additionally, volumetric changes over the electrode–electrolyte layer are likely to result in delamination of the electrolyte and micro-crack formation [9]. The change in mechanical and microstructural proper- ties of the anode is expected to affect both the mechanical strength and the electrochemical performance of the cell. How- ever, the results of the studies might be highly dependent upon the powder processing technologies and cell fabrication techniques. This paper describes the response of the anode supports, fab- ricated from coarse and fine materials, to redox cycling. 0378-7753/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2006.09.074