Journal of Power Sources 196 (2011) 10601–10605 Contents lists available at SciVerse ScienceDirect Journal of Power Sources jo ur nal homep age: www.elsevier.com/locate/jpowsour Short communication Quantitative analysis of micro structural and conductivity evolution of Ni-YSZ anodes during thermal cycling based on nano-computed tomography Yong Guan a,b , Yunhui Gong c , Wenjie Li a,b , Jeff Gelb e , Lei Zhang d , Gang Liu a,b , Xiaobo Zhang a,b , Xiangxia Song a,b , Changrong Xia d , Ying Xiong a,b , Haiqian Wang c,∗ , Ziyu Wu a,b , Yangchao Tian a,b,∗∗ a National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, People’s Republic of China b School of Nuclear Science and Technology, University of Science and Technology of China, Hefei, Anhui 230029, People’s Republic of China c Hefei National Laboratory for Physical Sciences at Microscale, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China d Materials of Science and Engineering, University of Science and Technology of China, Hefei, Anhui 230026, People’s Republic of China e Xradia Inc., 4385 Hopyard Road, Suite 100, Pleasanton, CA 94588, USA a r t i c l e i n f o Article history: Received 21 July 2011 Received in revised form 19 August 2011 Accepted 19 August 2011 Available online 26 August 2011 Keywords: Anode Thermal cycles Ni agglomeration Microstructure evolution Nano-computed tomography a b s t r a c t Understanding the mechanism of degradation in solid oxide fuel cells (SOFCs) using nickel/yttria- stabilized zirconia (Ni-YSZ) as the anode material is very important for the optimization of cell performance. In this work, the effects of thermal cycling on the microstructure of the Ni-YSZ anode are explored using the three-dimensional X-ray nano computed tomography (nano-CT) imaging tech- nique. It is found that the average Ni particle size increased with thermal cycling, which is associated with the decreased connectivity of the Ni phase and the three-phase-boundary (TPB) length. Moreover, the conductivities of the anode samples are also reduced with the increase in thermal cycle times. The implication of these observations is discussed in terms of the relationship between the conductivity and connectivity of the Ni phase. © 2011 Elsevier B.V. All rights reserved. 1. Introduction In recent years, much attention has been paid to fuel cells because of their ability to produce clean and efficient energy by directly converting chemical energy into electricity. A solid oxide fuel cell (SOFC) uses a hard ceramic electrolyte and operates at very high temperatures, between 500 and 1000 ◦ C, where good ionic conductivity occurs. The electrolyte is usually yttria-stabilized zir- conia (YSZ), which conducts oxygen ions but not electrons. SOFC anodes also require an electronic-conducting phase, for which Ni is typically matched to YSZ. The electrodes are porous, enabling the transport of gasses along with ions and electrons. Chemical reac- tions take place where the ionic, electronic, and gas-conduction phases meet, which are called the triple-phase boundaries (TPBs). Commercial applications of SOFCs for stationary power sources require their stable performance over long periods ∗ Corresponding author. ∗∗ Corresponding author at: National Synchrotron Radiation Laboratory, University of Science and Technology of China, Hefei, Anhui 230029, People’s Republic of China. Tel.: +86 551 3601844; fax: +86 551 5141078. E-mail addresses: hqwang@ustc.edu.cn (H. Wang), ychtian@ustc.edu.cn (Y. Tian). of time (>40,000 h); therefore, SOFCs must exhibit mechani- cal, thermal, chemical, and electrical stability during long-term high-temperature operation. Unfortunately, the electrochemical performance of SOFCs is inevitably degraded during the cell lifetime [1,2]. It is therefore of great importance to understand the degra- dation mechanism of SOFCs to improve the operation time and optimize the performance. Numerous degradation mechanisms for the Ni-YSZ anode have been proposed [3,4], and among them a pre- vailing interpretation is the rearrangement and coarsening of the Ni phase [5,6]. If the Ni phase is not stable during operation, the functions of the Ni phase, such as providing a high amount of TPBs for electrochemical reactions, can be significantly altered. It is diffi- cult to define the effect of local conditions such as temperature on any degradation mechanisms [7]. Alternatively, high-temperature thermal-cycling experiments in conjunction with microstructural analysis on the Ni-YSZ anode provide a means of examining the changes in the Ni-YSZ anode under a defined condition. To this end, three-dimensional (3D) information regarding the full pore networks of the anode is desired because it plays a cru- cial role in modeling, simulating and establishing the correlation between anode microstructure and electrical properties of an SOFC. Recently, the 3D microstructure of SOFC electrodes has been directly measured by scanning electron microscopes equipped with a focused-ion beam (FIB-SEM) [8–12]. By applying these 3D 0378-7753/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2011.08.083