DOI: 10.1002/adfm.200700505 Micro Solid Oxide Fuel Cells on Glass Ceramic Substrates** By Ulrich P. Muecke, Daniel Beckel, Andre´Bernard, Anja Bieberle-Hu¨tter, Silvio Graf, Anna Infortuna, Patrik Mu¨ller, Jennifer L. M. Rupp, Julian Schneider, and Ludwig J. Gauckler* 1. Introduction Power for portable electronic devices, such as, laptops or mobile phones is usually supplied by rechargeable batteries. However, the energy requirements of future devices are projec- ted to increase at a faster rate than the capacity of rechargeable batteries and it becomes difficult to provide reasonable running times without increasing battery size. [1,2] The desire for alternative small-scale energy supplies created substantial interest in miniaturized fuel cells, from which more energy per volume and weight is expected than from batteries. [3,4] Furthermore, they potentially allow instant refueling. There are currently three types of microfuel cells under investigation: micropolymer electrolyte/proton exchange mem- brane fuel cells (m-PEMFCs), microdirect methanol fuel cells (m-DMFCs), and micro solid oxide fuel cells (m-SOFCs). The highest power densities of m-PEMFCs and m-DMFCs with air as oxidant and hydrogen or diluted methanol as fuel are reported to be 130 mW cm 2 at 40 8C and 100 mW cm 2 at 60 8C, respec- tively. [5–10] When oxygen is used at the cathode side, the power density can be improved to 195 mW cm 2 at 25 8C for m-PEMFCs. [11] However, oxygen is not a viable oxidant for portable applications as it has to be provided from a separate tank. The storage and distribution of pure hydrogen, which is needed as fuel for m-PEMFCs, is difficult at present and current storage solutions do not scale down efficiently. [12,13] Both m-PEMFCs and m-DMFCs also face challenges in water management and thermal control. In m-DMFCs, methanol cross-over is a fundamental problem and special solutions for pumping the liquid fuel need to be incorporated. [14] In contrast to the polymer-based fuel cells, SOFCs offer the advantage of running on a variety of fuels like hydrogen or liquefied petroleum gas. The higher energy density of, i. e., butane (7290 W h L liquid 1 and 12 600 W h kg 1 ) compared to hydrogen (2330 W h L liquid 1 and 32 900 Wh kg 1 ) or methanol (4384 W h L 1 and 5600 W h kg 1 ) [8] , would offer longer runtimes at the same weight or volume. The theoretical energy density of rechargeable lithium-ion batteries, for comparison, is 410 W h kg 1 . [15] m-SOFC systems are likely to contain a fuel pre-reformer [16] to reduce the coking tendency at the anode by converting the hydrocarbon fuel to syngas, [17] and a post- combustor to oxidize hydrogen and carbon monoxide in the fuel cell exhaust to water and carbon dioxide. [1] The targeted operating temperature of m-SOFCs is 300–600 8C, which is considerably lower than that of their larger counterparts operating at 800–1 000 8C. Several studies were conducted on single thin film components for m-SOFCs, examining their preparation and FULL PAPER [*] Prof. L. J. Gauckler, Dr. U. P. Muecke, Dr. D. Beckel, Dr. A. Bieberle- Hu ¨tter, S. Graf, Dr. A. Infortuna, Dr. J. L. M. Rupp, J. Schneider Department of Materials, Nonmetallic Inorganic Materials ETH Zurich Wolfgang-Pauli-Str. 10, 8093 Zurich (Switzerland) E-mail: ludwig.gauckler@mat.ethz.ch Prof. A. Bernard, P. Mu¨ller Institute for Micro- and Nanotechnology, NTB Interstate University of Applied Sciences Buchs Werdenbergstr. 4, 9471 Buchs (Switzerland) [**] Financial support from the Commission for Technology and Inno- vation (grants: KTI 7085.2 DCPP-NM and KTI 8446.1 DCPP-NM), Center of Competence Energy and Mobility (CCEM), Bundesamt fu¨r Energie (BfE), Swiss Electric Research and European Union within the REAL-SOFC project is gratefully acknowledged. Miniaturized solid oxide fuel cells are fabricated on a photostructurable glass ceramic substrate (Foturan) by thin film and micromachining techniques. The anode is a sputtered platinum film and the cathode is made of a spray pyrolysis (SP)-deposited lanthanum strontium cobalt iron oxide (LSCF), a sputtered platinum film and platinum paste. A single-layer of yttria-stabilized zirconia (YSZ) made by pulsed laser deposition (PLD) and a bilayer of PLD–YSZ and SP–YSZ are used as electrolytes. The total thickness of all layers is less than 1 mm and the cell is a free-standing membrane with a diameter up to 200 mm. The electrolyte resistance and the sum of polarization resistances of the anode and cathode are measured between 400 and 600 8C by impedance spectroscopy and direct current (DC) techniques. The contribution of the electrolyte resistance to the total cell resistance is negligible for all cells. The area-specific polarization resistance of the electrodes decreases for different cathode materials in the order of Pt paste > sputtered Pt > LSCF. The open circuit voltages (OCVs) of the single-layer electrolyte cells ranges from 0.91 to 0.56 V at 550 8C. No electronic leakage in the PLD–YSZ electrolyte is found by in-plane and cross-plane electrical conductivity measurements and the low OCV is attributed to gas leakage through pinholes in the columnar microstructure of the electrolyte. By using a bilayer electrolyte of PLD–YSZ and SP–YSZ, an OCV of 1.06 V is obtained and the maximum power density reaches 152 mW cm 2 at 550 8C. Adv. Funct. Mater. 2008, 18, 1–11 ß 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim 1