Viewpoint Paper A study of the methane tolerance of LSCM–YSZ composite anodes with Pt, Ni, Pd and ceria catalysts Ju-Sik Kim, Vineet V. Nair, John M. Vohs and Raymond J. Gorte * Department of Chemical and Biomolecular Engineering, University of Pennsylvania, Philadelphia, PA 19104, USA Received 19 March 2010; revised 5 June 2010; accepted 7 June 2010 Available online 12 June 2010 Abstract—The performance of solid-oxide-fuel-cell anodes based on composites of LSCM and YSZ containing 0.5 wt.% metal cat- alyst was studied to understand the performance and stability of these anodes. Electrodes containing Pt were found to be stable in CH 4 but carbon deposits with granular or filamentous morphologies were found with electrodes containing either 0.5 wt.% Pd or Ni. Carbon deposition with both Pd and Ni was greatly suppressed by the addition of 10 wt.% ceria as a co-catalyst. Ó 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Solid oxide fuel cells; Methane; Yttria-stabilized zirconia; Ceria 1. Introduction Composites of Ni and yttria-stabilized zirconia (YSZ) are the most commonly used anodes in solid oxide fuel cells (SOFCs). While anodes of this design have numer- ous positive characteristics, including ease of fabrication, low impedance when operating with H 2 fuel and catalytic activity for the steam reforming of CH 4 , they also have several drawbacks such as low redox stability, high cata- lytic activity for coke formation from hydrocarbons and low sulfur tolerance [1–4]. These latter traits have moti- vated research into the development of anodes based only on ceramic components [5,6], which in theory would have much higher redox and hydrocarbon stabilities, as well as better sulfur tolerance. One of the main obstacles in the development of ceramic anodes is identifying materials that have both sufficient electronic conductivity and cat- alytic activity. This problem can be solved by using sepa- rate functional and conduction layers, in which a thin functional layer near the electrolyte is optimized for elec- trochemical activity, while current collection is handled by a thicker layer further from the electrolyte [7,8]. Cata- lytic activity can be enhanced through the addition of reducible transition metals, introduced into the func- tional layer either by infiltration with metal salts [7,9] or by incorporation into the oxide lattice and subsequent re- lease upon reduction [10]. Work in our laboratory has focused on the properties of functional layers prepared by infiltration of ceramic conductors and catalytic metals into porous YSZ scaf- folds that had been pre-sintered onto the YSZ electrolyte. Electrodes prepared in this manner exhibit a number of important advantages. First, composites prepared by infiltration are not random due to the fact that the con- ductive phase is added into the pores of the existing scaf- fold. Because of this, conductivity can be achieved at volume fractions lower than 30%, the percolation thresh- old for random composites [11], thereby allowing for greater flexibility in optimizing the electrode microstruc- ture. Due to the composition and non-random structure, the coefficient of thermal expansion (CTE) of the elec- trode remains closer to that of the YSZ component, rather than the weighted average of the two phases [12]. This allows for the use of a wider range of electrochemi- cally active materials since the CTE of the two compo- nents do not need to be so closely matched. Second, the YSZ phase in the electrode composite can be sintered at higher temperatures, decreasing grain boundary resis- tances in the YSZ phase at the electrode–electrolyte inter- face. This enhances the conduction of oxygen ions into the electrode and provides for a long three-phase bound- ary (TPB) [13]. Finally, because each component is added separately, it is relatively easy to compare the effect of dif- ferent types of promoters. This facilitates mechanistic studies since the enhancements obtained by adding each component can be systematically studied, while holding the overall microstructure relatively constant [14]. 1359-6462/$ - see front matter Ó 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.scriptamat.2010.06.016 * Corresponding author. Fax: +1 215 573 2093; e-mail: gorte@ seas.upenn.edu Available online at www.sciencedirect.com Scripta Materialia 65 (2011) 90–95 www.elsevier.com/locate/scriptamat