Journal of Power Sources 200 (2012) 14–20 Contents lists available at SciVerse ScienceDirect Journal of Power Sources jou rnal h omepa g e: www.elsevier.com/locate/jpowsour Solid oxide fuel cell with NiCo–YSZ cermet anode for oxidation of CO/H 2 fuel mixtures Julie S. O’Brien, Javier B. Giorgi ∗ Centre for Catalysis Research and Innovation, Department of Chemistry, University of Ottawa, 10 Marie Curie Prvt., Ottawa, Ontario, Canada K1N 6N5 a r t i c l e i n f o Article history: Received 1 September 2011 Received in revised form 21 October 2011 Accepted 22 October 2011 Available online 25 October 2011 Keywords: SOFC Anode Syngas Hydrogen Carbon monoxide Cobalt Nickel Cermet a b s t r a c t The suggestion has been made in the literature that solid oxide fuel cells (SOFCs) operated with syngas as fuel may be viable in certain gas ratio regimes. We have explored this hypothesis with a promising bimetallic anode material. SOFCs with Ni 0.7 Co 0.3 –YSZ cermet anodes were operated with CO/H 2 mixtures in the full concentration range. Electrochemical impedance spectroscopy and voltammetry measure- ments were employed to measure the exchange current density (i 0 ) values of each fuel mixture. The fuel mixtures of CO/H 2 ratios corresponding to the range 20/80 and 30/70 were found to have i 0 values larger than that of pure H 2 with the same cell. For these two fuel ratios, an improvement of 5–8 times, respectively, in the exchange current density has been observed. Higher CO/H 2 fuel ratios in the range of 60/40–80/20 produced i 0 values lower than H 2 , as carbon poisoning is operational in this region. Con- tinuous running of a cell with fuel ratio 25/75 CO/H 2 for 7 days produced i 0 values above the values for pure H 2 as has been recently suggested. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Solid oxide fuel cells (SOFCs) are gaining a lot of interest due to their fuel flexibility, high fuel-electricity conversion efficiency, and long-term stability for practical applications [1,2]. Among many common fuels such as hydrogen, heavier liquid fuels such as alco- hols (methanol, ethanol, etc.), hydrocarbons (methane, ethane, etc.) and biodiesel are being considered. At common operating tem- peratures for SOFCs (800–1000 ◦ C), heavier liquid fuels undergo thermodynamic decomposition to form predominantly hydrogen and carbon monoxide [3,4]. Because of this, a greater understand- ing of how SOFCs utilize and tolerate different ratios of H 2 and CO is essential. Additionally, independently produced syngas can be used directly as a fuel. With a mixture of H 2 and CO as fuel, each has a corresponding electrochemical oxidation reaction at the anode: H 2 + O 2- → H 2 O + 2e - (1) CO + O 2- → CO 2 + 2e - (2) In a recent computational paper, Andreassi et al. [5] found the contribution made by CO direct oxidation to be 12.5% for a cell running on a fuel ratio of 80/20 CO/H 2 at 800 ◦ C with a Ni–8YSZ ∗ Corresponding author. Tel.: +1 613 562 5800x6037; fax: +1 613 562 5170. E-mail address: jgiorgi@uottawa.ca (J.B. Giorgi). cermet anode. This effect becomes increasingly important at high current densities, where the model must consider both H 2 and CO direct oxidation in order to best simulate what is observed by experiment. Therefore, CO direct oxidation is present under SOFC operation conditions and is non-negligible. With a mix of H 2 and CO in the fuel feed, the water–gas shift reaction (WGSR) must also be considered: CO + H 2 O → CO 2 + H 2 (3) This equation shows that when appreciable concentrations of water vapour are present in the fuel feed, particularly at high fuel utilization, the CO concentration will be lowered and H 2 produced. The kinetics of this reaction are fast and favourable, much more so when compared to the direct oxidation of CO, so the presence of water vapour will cause the reaction to proceed, generating H 2 . However, according to Andreassi et al. [5], considering only the WGSR (and not CO oxidation) underestimates the voltage given experimentally. Traditionally, the most common anode material for SOFCs with a YSZ electrolyte layer is a Ni–YSZ cermet. Although Ni has a high activity for H 2 electrochemical oxidation, it is not an effective cata- lyst for CO oxidation. Additionally, because H 2 has a lower surface diffusion resistance on Ni when compared to CO, the amount of H 2 which can be oxidized is expected to be higher. This contributes to a rate constant which is 2–3 times higher at temperatures between 0378-7753/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.jpowsour.2011.10.080