Bo Jiang, Thomas Maeder, Paul Muralt, Dimos Poulikakos
Recently, the development of micro-scale solid oxide fuel cells (µ-SOFCs) has become a promising research topic in the area of portable energy production. A µ-SOFC system, which can provide 1 to 2 W electrical power under an operating temperature of 550°C 1-2, mainly consists of a fuel processor, an electrochemical power generator, and a post combustor. The role of the fuel processor is to generate a hydrogen-rich product stream that is fed to the power generation module. In previous works, various micromachined fuel reformers based on microelectromechanical system (MEMS) technology have been demonstrated to achieve high-yield syngas generation from liquid hydrocarbons 3-5. However, MEMS-based micro-reformers require time-consuming and expensive fabrication processes, and face critical issues concerning electrical and fluidic interconnects. Conversely, 'traditional' thick film-technology is a simple and low-cost fabrication route, allows integration of a wide palette of materials by a convenient printing technique, and has a proven track record in harsh environments 6. Here, we propose to apply thick-film technology to a fuel-processing platform for the development of µ-SOFC systems. The thick-film based fuel processor consists of a self-sensing heating element, a fluidic carrier comprising a catalyst chamber, and a ceramic substrate. The heating element consists of two independent thick-film platinum conductor meanders, which are screen printed at the bottom of the fluidic carrier, and provide relatively homogeneous heating of the catalytic reforming zone up to 700°C 7. Due to their temperature dependence of resistance, the thick-film Pt heaters double as temperature sensors and thus allow integrated temperature control of the fuel processing. The fluidic carrier was made of two pieces of (12 mm × 75 mm × 0.7 mm) borosilicate glass (Schott AF32), bonded by a screen-printed glass frit seal (Ferro IP760c), which also patterns the fluidic channels in the carrier. Multiple glass paste prints allow for building up the channel height (i.e. distance between glass plates) up to ca. 150 µm. The catalyst is placed into an open chamber on the top plate of the fluidic carrier by dispensing, and is capped by a piece of AF32 glass (12 mm x 13.8 mm) using the same glass frit bonding technique. The elongated shape of the fluidic carrier and low thermal conductivity of the glass efficiently decouples the heat generated in the "hot" catalyst area from the other "cold" end of the carrier, allowing conventional low-temperature electrical and fluidic interconnections. With a heating power below 8 W, the platform is able to quickly heat the active zone to 700°C, while maintaining the electrical and fluidic connections below 50°C. The performance of isobutane reforming was evaluated, studying the impact of design parameters such as the catalyst chamber dimension, and geometry of the thick-film Pt resistor. The talk will present and discuss the studied fabrication processes including the glass frit and catalyst paste formulation, screen printing and dispensing processes, and show the performance of the platform with results obtained on thermal characterization and gas reforming. The heat output of exothermic reactions is well observed. Keywords solid oxide fuel cell, fuel processer, hydrogen production Reference [1] S. Rey-Mermet and Paul Muralt, Solid State Ionics, 179 (2008) 1497 -1500 [2] A. Bieberle-Hütter et al., Journal of Power Source, 177 (2008) 123-130 [3] J. D. Holladay et al., Chemical Reviews, 104(2004) 4767-4789 [4] K. Yoshida et al., Journal of Micromechanical and Microengineering, 16 (2006) S191-S197 [5] A. J. Santi-Alvarez et al., Energy & Environmental Science, 4 (2011) 3041-3050 [6] T. Maeder et al., Proceedings of 7th CICMT, San Diego (USA), 2011 [7] B. Jiang et al., Sensors and Actuators B, 2012, under review
2012
