Metal hydride fuel cell
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Metal hydride fuel cells are a subclass of alkaline fuel cells that are currently in the research and development phase. A notable feature is their ability to chemically bond and store hydrogen within the cell. This feature is shared with direct borohydride fuel cells, although the two differ in that MHFCs are refueled with pure hydrogen. Though the absorption characteristics of metal hydrides (around 2%) is far lower than sodium-borohydrides and other "light" metal hydrides (around 10,8%)[1], prototypes have been claimed to demonstrate a number of interesting characteristics:
- Ability to be recharged with electrical energy (similar to NiMH batteries);
- Low operating temperatures (down to -20°C);
- Fast kinetics;
- Extended shelf life;
- Fast "cold start" properties;
- Ability to operate for limited periods of time with no external hydrogen source, enabling "hot swapping" of fuel canisters.
Metal hydride fuel cells are currently being researched by ECD Ovonics, as well as by the Japanese National Institute of Advanced Industrial Science and Technology (AIST). Though similar, the two MHFC concepts use different catalysts.[2][3]
Thus far, neither research project has produced a demonstratable model outside of a laboratory - only publications and patents - and significant efficiency hurdles have yet to be overcome. The Ovonics and AIST metal hydride fuel cells claim current densities of only 250mA/cm2 and 20mA/cm2, respectively, versus typical PEMFC performance at 1A/cm2.
[edit] Bibliography
- Appleby, John, “High Power Alkaline Fuel Cell with Intrinsic Energy Storage”, 204th Meeting of the Electrochemical Society, The Electrochemical Society, Inc.
- Wang, X.H.; et al. (1999). "Electrochemical properties of Ml(NiCoMnCu)5 used as an alkaline fuel cell anode". Journal of Alloys and Compounds 293-295: 833–837. doi:.
- Lee, S-M.; J.-H. Kim, H.-H. Lee, P S. Lee and J.-Y. Lee (2002). "The Characterization of an Alkaline Fuel Cell that Uses Hydrogen Storage Alloys". Journal of The Electrochemical Society 149 (5): A603–A606. doi:.
- Tanaka, H.; N. Kaneki, H. Hara, K. Shimada and T. Takeuchi (April 1986). "La-Ni System Porous Anode in an Alkaline Fuel Cell". Canadian Journal of Chemical Engineering 64: 267–271.
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