Journal of Power Sources 196 (2011) 6048–6054 Contents lists available at ScienceDirect Journal of Power Sources journal homepage: www.elsevier.com/locate/jpowsour Effects of crystal Structure of yttria- and scandia-stabilized zirconia in nickel-based SOFC anodes on carbon deposition and oxidation behavior Hirofumi Sumi, Pramote Puengjinda, Hiroki Muroyama, Toshiaki Matsui, Koichi Eguchi ∗ Department of Energy and Hydrocarbon Chemistry, Graduate School of Engineering, Kyoto University, Nishikyo-ku, Kyoto 6158510, Japan article info Article history: Received 22 February 2011 Received in revised form 22 March 2011 Accepted 29 March 2011 Available online 6 April 2011 Keywords: Solid oxide fuel cell (SOFC) Internal reforming Carbon deposition Raman spectroscopy Temperature programmed oxidation abstract The effect of crystal structure of yttria- (YSZ) and scandia-stabilized zirconia (ScSZ) in nickel-based SOFC anodes was investigated in relation with carbon deposition and oxidation behavior in methane fuel. The lattice parameter of the zirconia decreased by the dissolution of 1–2 mol%Ni to YSZ and ScSZ. For Ni-doped ScSZ, the lattice parameter of the zirconia increased by the Ni dissolution, and the crystal structure of the zirconia was modified after reduction treatment. New finer Ni particles were formed around original Ni grains accompanied by the decrease in Ni solubility to ScSZ after reduction treatment. Carbon deposition was initiated near the boundary between Ni particles and YSZ (or ScSZ) substrate in dry methane atmosphere. Furthermore, the rod-shaped carbon was observed to grow from the new finer Ni particles on the ScSZ substrate. On the other hand, a large amount of amorphous carbon was promoted to be deposited on Ni-YSZ cermet at a high temperature of 1273 K. The amorphous carbon, however, was oxidized at lower temperatures than graphite. The carbon deposition and oxidation behavior was strongly affected by the morphology and crystallinity of deposited carbon. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Solid oxide fuel cells (SOFCs) are power sources with high energy conversion efficiency. Power generation by direct supply of hydrocarbon is possible for SOFCs through the internal reforming for hydrocarbon fuel, because of their high temperature opera- tion around 1073 - 1273 K. However, solid carbon can be easily deposited on the anode due to direct supply of hydrocarbon at high temperatures, and it causes the electrode deterioration. For methane fuel, no carbon is deposited under internal and/or external steam reforming at 1073 - 1273 K and H 2 O/CH 4 ≥ 1 in the thermo- dynamic equilibrium [1,2]. The H 2 O/CH 4 ratio possibly decreases, when gas flow and steamer systems is broken down. Therefore, fuel electrode with high durability against carbon deposition is desired to be developed. For instance, Cu-based and Ru-doped anodes are reported to have high tolerance to carbon deposition [3–7]. How- ever, the Cu-based anodes have less activity for reforming, and the Ru-doped anodes are more expensive than conventional Ni-based anodes. It was previously reported that the dopant into zirconia affected the electrode performance and durability in the Ni-based anodes [8,9]. Ni-scandia stabilized zirconia (ScSZ) anode was less suffered from carbon deposition than Ni-yttria stabilized zirconia (YSZ) anode under power generation by internal reforming of methane ∗ Corresponding author. Tel.: +81 0 75 383 2519; fax: +81 0 75 383 2520. E-mail address: eguchi@scl.kyoto-u.ac.jp (K. Eguchi). at low H 2 O/CH 4 ratios and at 1273 K. While fibrous and rod-shaped graphite was observed on the Ni-ScSZ anode after power genera- tion, a large amount of amorphous carbon was deposited on the Ni-YSZ anode. Several studies have also reported that the ratio of amorphous carbon and crystalline graphite depended on the oxide species such as YSZ, ScSZ, Sm-doped ceria and (La,Sr)(Ga,Mn)O 3 in SOFC anodes [10–12]. Furthermore, the carbon deposition behav- ior depended on the operating temperature [9,13,14]. The rate of carbon deposition for the Ni-YSZ anode was faster than that for the Ni-ScSZ anode at 1273 K, whereas the order was opposite at 1123 K. However, the reason for the selectivity of oxide species and the effect of operating temperature has not been clarified so far. Cubic zirconia phase is generally stabilized by doping yttria and scandia for SOFC electrolytes [15,16]. The crystal structure of YSZ and ScSZ was previously evaluated by X-ray diffraction and Raman spectroscopy [17–22]. The ScSZ phase was reported to be more sensitive to the treatment condition than YSZ phase. Matsui et al. reported that the ScSZ phase was affected by the heat treat- ment temperature [20]. Kishimoto et al. and Puengjinda et al. have reported that the ScSZ phase was changed from cubic to rhom- bohedral during reduction–oxidation (redox) treatment [21,22] Moreover, the cubic phase of the zirconia is stabilized by dissolution of a small amount of nickel into zirconia [23–25]. The difference in the stability of zirconia phase is likely to affect the change of the carbon deposition behavior for Ni-based SOFC anodes. Catalytic properties of SOFC anode materials were evaluated by several studies. The interaction between nickel and zirconia was confirmed to become strong with increasing Ni content for Ni- 0378-7753/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2011.03.092