Enhanced stability of Ni–Fe/GDC solid oxide fuel cell anodes for dry methane fuel Hyuk Kan, Hyunjoo Lee ⁎ Department of Chemical and Biomolecular Engineering, Specialized Graduate School of Hydrogen and Fuel Cell, Yonsei University, Seoul 120-749, South Korea abstract article info Article history: Received 27 May 2010 Received in revised form 21 July 2010 Accepted 23 July 2010 Available online 6 August 2010 Keywords: Stability SOFC Ni–Fe Alloy Anode catalyst Methane The addition of Fe into Ni/GDC (Gadolinium-Doped Ceria) anodes significantly improved the long-term stability of SOFC. While a Ni/GDC anode failed to operate after 12 h at a current density of 0.2 A cm -2 and 650 °C with dry methane flow, the cell performance of a Ni 0.9 Fe 0.1 /GDC anode showed no degradation over 50 h. The outlet gas of SOFC was analyzed by mass spectrometry, and the results revealed that methane was oxidized more completely on a Ni–Fe/GDC anode compared to a Ni/GDC anode. The change in catalytic properties due to the addition of Fe caused methane fuel oxidized more completely, which enhanced the long-term stability of the cell. © 2010 Elsevier B.V. All rights reserved. 1. Introduction Solid oxide fuel cells (SOFC) have been actively investigated due to their high energy efficiency and potential operation with various hydrogen and hydrocarbons fuels [1,2]. Hydrogen is currently produced from hydrocarbons by steam-reforming reaction; thus, the direct use of hydrocarbons in SOFCs would reduce overall energy costs and increase the efficiency of the cell [3,4]. Operating temperatures greater than 800 °C cause significant problems such as electrode sintering and interfacial diffusion between the electrode and the electrolyte. Moreover, high operating tempera- tures limit the types of materials that can be used in the cell and decrease the mechanical strength due to discrepant expansion [5]. Due to the aforementioned limitations, an intermediate temperature range is more desired in SOFC. While yittrium-stabilized zirconia (YSZ) is often used in high temperature SOFCs, YSZ does not display sufficient ionic conductivity at intermediate temperatures. New electrolytes with high ionic conductivity at intermediate tempera- tures have been actively investigated [6–8]. Ceria-based materials showed significantly higher ionic conductivity than YSZ and enhanced direct oxidation of hydrocarbons due to rapid lattice oxygen mobility [9,10]. Anodic materials also require electron conductors that can collect electrons generated during the oxidation of hydrocarbon fuels. Nickel is the most popular electron conductor because it possesses high catalytic activity and is stable under the harsh conditions typically encountered during the cell fabrication process. However, severe coking occurs when hydrocarbons are treated on a nickel surface at high temperature. To avoid this problem, other metals such as copper have been investigated as an electron conductor. However, copper is not stable above 1100 °C (m.p. = 1083 °C), although higher tempera- tures are required to fabricate a high quality SOFC single cell. Carbon deposition on the nickel surface is caused by pyrolysis reaction or the Boudouard reaction (2CO (g) →C (s) + CO 2 (g)) [4,11]. Pyrolysis occurs above 700 °C, while the thermodynamic equilibrium of the Boudouard reaction is shifted to the right at lower temperatures [12]. At operating temperatures below 700 °C, carbon deposition occurs mainly due to Boudouard reaction. Therefore, Boudouard reaction should be avoided below 700 °C to minimize the carbon deposition, which causes the degradation of cell performance. In this study, the cell performance and long-term stability of SOFCs with Ni–Fe bimetallic catalysts were evaluated at 650 °C under a flow of dry methane. The addition of 10% Fe to the anode catalyst increased the power density of the cell, and no degradation in cell performance was observed. The catalytic properties of Ni/GDC anodes were improved in the presence of Fe causing methane fuel oxidized more completely, leading to enhanced cell stability. 2. Experimental section NiO–Fe 2 O 3 /GDC catalysts were prepared using a solid-state reaction method. 55 wt.% of Fe 2 O 3 (Aldrich, 99%) and NiO (J.T Baker), 36 wt.% of GDC (Gd 0.1 Ce 0.9 O 2 , Rhodia), and 9 wt.% of starch (Aldrich) were mixed by ball-milling in ethanol. The ratio of Fe to Ni was changed from 0 wt.% to 50 wt.%. The mixture was dried at 100 °C for 24 h and pressed at 100 MPa into a disc with a diameter of 36 mm and a thickness of 1.2 mm. The pellets were sintered at 1200 °C for 3 h in air. GDC (Gd 0.1 Ce 0.9 O 2 , Rhodia) slurry was then applied onto the Catalysis Communications 12 (2010) 36–39 ⁎ Corresponding author. Tel.: +82 2 2123 5759; fax: +82 2 312 6401. E-mail address: azhyun@yonsei.ac.kr (H. Lee). 1566-7367/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.catcom.2010.07.014 Contents lists available at ScienceDirect Catalysis Communications journal homepage: www.elsevier.com/locate/catcom