Investigation of ammonium polyphosphate metal oxide composite ceramics as electrolytes for fuel cells operating in the intermediate temperature regime
Zusammenfassung der Projektergebnisse
Fuel cells have attracted worldwide attention as a clean power source because of their high efficiency in energy conversion and low emissions. The current polymer electrolyte membrane fuel cells (PEMFCs) generally employ polymer membranes like Nafion® as a proton conducting electrolyte and have to be operated below the boiling point of water for keeping the required high proton conductivity. At these temperatures, CO poisoning is a severe problem if the cell is operated on other fuels other than pure hydrogen. Furthermore, if the cell is operated directly using alcohol fuel, high loadings of noble metal catalysts are required to compensate for the low catalytic activity and internal CO poisoning. The ability of PEMFCs or direct alcohol fuel cell to operate at higher temperatures provides benefits such as faster electrode kinetics and greater tolerance to impurities in the fuel stream. Therefore, considerable effort has recently been devoted toward the development of solid-state proton conductors with conductivities more than 10^-2 S cm-1 in the temperature range of 150-300 °C. This project financially supported by DFG is aimed at developing a solid-state proton conductor with conductivities more than 10^-2 S cm-1, which can be stably operated in the intermediate temperature range. A promising candidate is the ammonium polyphosphate (abbreviated as APP) based electrolyte. However, pure phase APP is not stable at temperature more than 200 °C. In the past decade, our group in TUM has been investigating the APP based composite electrolyte for intermediate temperature fuel cells, mainly focusing on improvement of the thermal stability and proton transport properties of APP based materials. Our project follows the strategy of preparing APP based composites by addition of oxides, such as SiO2 and/or TiO2. We use different approaches to prepare the composites, including ball milling and sol-gel methods. NH4PO3/MO2 (M=Si, Ti) composite materials with superior conductivity were prepared by a sol-gel method and the composition was optimized based on the proton conductivity. Importantly, it was found that microstructure has a significant effect on conductivities of the composites at higher temperature. The approaches suggested in this work provide the possibility to obtain a solid-state proton conductor with superior conductivities, excellent thermal stability and controlled microstructures. The APP based composite materials are potential for application as electrolytes for intermediate temperature fuel cells.
Projektbezogene Publikationen (Auswahl)
- Fabrication and characterization of solid state proton conductor (NH4)2SiP4O13-NH4PO3 for fuel cells operated at 150-250 °C. Solid State Ionics 2006, 177, 2413-2416
X.L. Chen, Z. Huang, C.R. Xia
- NH4PO3/SiO2 composite as electrolyte for intermediate temperature fuel cells. Solid State Ionics 2006, 177, 2417-2419
L. Liu, H. Tu, C. Cremers, U. Stimming
- Solid state protonic conductor NH4PO3-(NH4)2Mn(PO3)4 for intermediate temperature fuel cells. Electrochim. Acta 2006, 51, 6542-6547
X.L. Chen, X. Li, S. Jiang, C.R. Xia, U. Stimming
- Synthesis and Characterization of NH4PO3 based composite with superior proton conductivity for intermediate temperature fuel cells. The Conference on Proton Conductors: Materials and Mechanisms, Nov. 2007, Stuttgart, Germany
C.W. Sun, U. Stimming
- Water effect on the conductivity behavior of NH4PO3-based electrolytes for intermediate temperature fuel cells. Electrochim. Acta 2007, 52, 7835-7840
X.L. Chen, C.R. Xia, U. Stimming
- Synthesis and characterization of NH4PO3 based composite with superior proton conductivity for intermediate temperature fuel cells. Electrochim. Acta 2008, 53, 6417-6422
C.W. Sun, U. Stimming
