Low-temperature solid-oxide fuel cells
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Energy Research Center, University of Maryland, USA; [email protected] Tatsumi Ishihara, International Institute for Carbon Neutral Energy Research, Kyushu University, Japan; [email protected] John Kilner, Department of Materials, Imperial College London, UK; [email protected] DOI: 10.1557/mrs.2014.192
© 2014 Materials Research Society
MRS BULLETIN • VOLUME 39 • SEPTEMBER 2014 • www.mrs.org/bulletin
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LOW-TEMPERATURE SOLID-OXIDE FUEL CELLS
methods, are widely used by the SOFC industry due to their inexpensive processing costs. In a conventional SOFC,2,3 a porous metaloxide composite (“cermet”) is generally used as the anode support layer. This is typically formed, for instance, from a ∼50:50 volumetric ratio of NiO to YSZ. Upon subsequent hightemperature exposure to the anode gas, NiO is reduced to Ni, creating the metallic conducting and catalytic phase, as well as opening up porosity by the NiO to Ni volume contraction. A dense electrolyte film is then deposited on the anode support using one of the previously mentioned methods. These conventional processes require a subsequent high-temperature Figure 1. (a) Schematic diagram of a solid-oxide fuel cell (SOFC) with different magnifications from a stack cell to anode and cathode microstructures. (b) Commercially developed co-sintering step, and for some materials, this portable (250 W) and transportation (5 kW) SOFCs, and larger scale stationary (250 kW necessitates a buffer layer to suppress reaction and MW) SOFCs planned for commercial demonstration. APU, auxiliary power unit. City between the electrode and electrolyte. gas refers to the domestic natural gas supply in Japan. Images of units were cited from web page of developer. Further reduction to ∼1-μm-thick electrolytes to achieve LT-SOFCs is described by Prinz et al. In this microelectromechanical were achieved by the use of thin-film electrolytes and more systems (MEMS)-based approach, thinner electrolyte films are active anode and cathode materials in tailored composite deposited on a dense substrate, which is subsequently rendered structures.8,9 These ITSOFCs are finding numerous applicaporous.10–12 A typical example is ∼100 nm YSZ deposition on tions on a variety of hydrocarbon fuels, as shown in Figure 1b. a Si substrate followed by chemical etching of the Si to make However, a further decrease in operating temperature is it porous. These techniques are particularly important for still necessary to achieve a long service life (>10 years), as so-called “micro-SOFCs,”12 which are envisioned more for battery replacement than large-scale power generation. well as shorter time and lower energy start-up for transient The other approach, increasing the intrinsic electrolyte and load-following applications.8,9 These low-temperature SOFCs (LT-SOFCs), operating at ≤650°C, require more conducconductivity, is a fundamental area of research in materials tive electrolytes and/or the ability to deposit thinner (near to science that has been applied primarily to materials with fluosubmicron thickness) el
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