Recent advances in single-chamber fuel-cells: Experiment and modeling Yong Hao a , Zongping Shao b , Jennifer Mederos b , Wei Lai b , David G. Goodwin a , Sossina M. Haile b, ⁎ a Mechanical Engineering, California Institute of Technology, Pasadena, California 91125, USA b Materials Science, California Institute of Technology, Pasadena, California 91125, USA Received 16 January 2006; received in revised form 6 May 2006; accepted 6 May 2006 Abstract Single-chamber fuel cells (SCFC) are ones in which the fuel and oxidizer are premixed, and selective electrode catalysts are used to generate the oxygen partial pressure gradient that in a conventional dual-chamber design is produced by physical separation of the fuel and oxidizer streams. SCFCs have been shown capable of generating power densities above 700 mW/cm 2 with appropriate catalysts, making them potentially useful in many applications where the simplicity of a single gas chamber and absence of seals offsets the expected lower efficiency of SCFCs compared to dual-chamber SOFCs. SCFC performance is found to depend sensitively on cell microstructure, geometry, and flow conditions, making experimental optimization tedious. In this paper, we describe recent work focused on developing a quantitative understanding the physical processes responsible for SCFC performance, and the development of an experimentally-validated, physically-based numerical model to allow more rational design and optimization of SCFCs. The use of the model to explore the effects of fuel/oxidizer ratio, anode thickness, and flow configuration is discussed. © 2006 Elsevier B.V. All rights reserved. Keywords: Solid oxide fuel cell; Single chamber; Hydrocarbon fuels; Experiment and simulation 1. Introduction While solid oxide fuel cells (SOFCs) exhibit a number of attractive features for power generation, including high energy conversion efficiency, fuel flexibility and relatively inexpensive electrode materials, the high temperatures required for operation (800–1000 °C) introduce a number of challenges. In particular, for planar SOFCs, thermal expansion mismatches between components can lead to failure of the seals that separate anode and cathode chambers. One strategy for addressing this challenge is to utilize so-called ‘single chamber fuel cells’ (SCFCs) in which the fuel and oxidant are allowed to mix and anode and cathode reactions take place within the same physical chamber [1]. The functionality of SCFCs derives from the selectivity of the electrode catalysts, with the anode preferentially oxidizing the fuel and the cathode preferentially reducing oxygen. The resulting oxygen partial pressure gradient generated across the cell in turn generates an electrical potential gradient. Useful power outputs are typically obtained under fuel rich conditions relative to com- plete oxidation [1–3]. Although the power density and efficiency are typically lower than those of conventional dual-chamber SOFCs (as a consequence of incomplete fuel utilization and parasitic, non-electrochemical fuel oxidation), the latest advances in materials science and system design have greatly improved SCFC power densities, in part, by lowering the fuel cell operating temperature so as to minimize purely chemical oxidation of the fuel [2,3]. Despite the lower efficiency, SCFCs have advantages over dual- chamber SOFCs that are particularly relevant for portable power generation. Because complications due to sealing are eliminated, the SCFC greatly simplifies the system design and enhances the thermal and mechanical shock resistance, thereby enabling rapid start up and shut down. The relatively low temperatures (400– 600 °C) at which the most advanced SCFCs function also help to ease complications with on–off cycling. The reduced temperatures of operation provide additional benefits including expanding the choices of materials for fabrication of peripheral components and inhibiting carbon deposition via hydrocarbon cracking at the anode catalyst. Quite significantly, micro-SCFC systems can be designed Solid State Ionics 177 (2006) 2013 – 2021 www.elsevier.com/locate/ssi ⁎ Corresponding author. Fax: +1 626 395 3933. E-mail address: smhaile@caltech.edu (S.M. Haile). 0167-2738/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.ssi.2006.05.008