Development of a low temperature co-fired ceramic fuel processor for the micro-scale solid oxide fuel cell system

The miniaturized solid oxide fuel cells (µ-SOFCs) has become an intensively studied device for portable power generation technology due to its wide choice of hydrocarbon fuels, its high energy density and its great operation efficiency. It is being considered as a battery replacement [1]. The µ-SOFC system, which aims to provide electrical energy (≤ 10 W) at an operating temperature of ca. 550°C, consists of a fuel cell unit for the electrochemical conversion [2-3]; a fuel processing unit for the thermal start-up, fuel reforming and total oxidation of exhausts [4-5]; a system packaging that insulates the fuel cell unit from the operating temperature to the ambient as well as provides fluidic and electronic connections [6-8]; and an electronics module for regulating the power output. As a core module of the entire µ-SOFC system, various fuel processing units have been proposed and developed. Most of those modules have been based on microelectromechanical systems (MEMS), which however shows several critical limitations with regard to electrical and fluidic connections and system integration [9-10]. Here we propose a ceramic based meso-scale gas processer combined with thick film and low-temperature co-fired ceramic technology (LTCC). With an overall size of 12 × 30 × 10 mm3, the ceramic processor, made of Heraeus HeroLock 2000 LTCC materials, mainly functions as a meso-scale hotplate that has a cantilever shape to effectively decouple the heat at the hot zone produced by the start-up heater and/or exothermic fuel processing reactions from the cold zone, in which the temperature is near ambient and thus compatible with normal electrical and fluidic connections (Figure 1). Embedded cavities were integrated into the processor during the fabrication process by using a progressive lamination technique. A thick-film crack-free catalyst paste, containing rhodium-doped ceria-zirconia nanoparticles, was dispensed into the reaction chambers as packed catalytic beds for the processing reactions. An integrated thick-film platinum (Heraeus CL11-6109) heater provides the start-up energy for the exothermic reforming reaction of butane or methane as well as total oxidation reactions. Such a meso-scale monolithic ceramic reactor can carry out the gas processing in a thermally self-sustaining manner, rendering itself to be a functional packaging of the entire µ-SOFC system in the future. In this work, the fabrication process of the gas processor will be discussed in detail, and the results of the fuel processing reactions such as reforming, total oxidation and thermal start-up will be presented as well. References: [1] Bieberle-Hütter, A., Beckel, D., et al. Journal of Power Sources, 177(1), 123–130, (2008) [2] Rey-Mermet, S. and Muralt, P. Solid State Ionics, 179(27–32), 1497-1500, (2008) [3] Evans, A., Bieberle-Hütter, A., et al. Monatshefte für Chemie - Chemical Monthly, 140(9), 975–983, (2009) [4] Shao, Z., Haile, S. M., et al. Nature, 435(7043), 795–798, (2005) [5] Santis-Alvarez, A. J., Nabavi, M., et al. Energy & Environmental Science, 4(8), 3041, (2011) [6] Jiang, B., Maeder, T., Muralt, P. Proceedings, Power MEMS 2010, Leuven (BE), 2010 [7] Jiang, B., Muralt, P., et al. Sensors and Actuators B: Chemical, 175, 218–224, (2012) [8] Maeder, T., Jiang, B., et al. Proceedings, 7th International Conference on Ceramic Interconnect and Ceramic Microsystems Technologies (CICMT), San Diego (USA), 2011 [9] Hotz, N., Osterwalder, N., et al. Chemical Engineering Science, 63(21), 5193–5201, (2008) [10] Vaccaro, S., Malangone, L., Ciambelli, P. Industrial & Engineering Chemistry Research, 49(21), 10924–10933, (2010)