Metal hydride fuel cells are a subclass of alkaline fuel cells that have been under research and development,[1][2][3][4][5] as well as scaled up successfully in operating systems.[6][7] A notable feature is their ability to chemically bond and store hydrogen within the fuel cell itself.
Metal hydride fuel cells have demonstrated the following characteristics:[8][9][10]
Electrode active areas of metal hydride fuel cells have been scaled up from 60 cm2 to 250 cm2, enabling systems to be scaled up to 500 Watts.[11] The scaling up of electrode active areas also provided capabilities to develop higher power fuel cell stacks, each with 1500 Watts of power.[6] Metal hydride fuel cells have achieved a current density of 250 mA/cm2.[12] To test durability, fuel cell stacks were successfully operated for more than 7000 hours.[12]
During the earlier phases of product development, there was a focus on single fuel cells and fuel cell stacks composed of multiple cells. The target applications included critical backup power for military and commercial applications.[13] The next phase was to design and build complete fuel cell systems that could be taken outside of the laboratory. Initial 50 Watt laboratory-based demonstration systems were integrated into 50 Watt portable systems with more robust packaging and interfacing.[12] Additional developments in both the fuel cell stack and system integration enabled a 1.0 kW system, complete with an inverter and onboard hydrogen storage using metal hydride storage canisters, to be operated and demonstrated in public.[6][14] Further developments in metal hydride fuel cell systems were pursued for the field power needs of soldiers, resulting in a prototype system meeting deployment requirements.[15] In tandem with product development, there was also a focus on developing capabilities for manufacturing and testing.[16] Metal hydride fuel cell systems have been integrated into microgrid systems at military bases for testing and evaluation.[17] Despite challenges,[18] the military maintains an active interest in fuel cells for a broad range of applications, including unmanned aerial vehicles, autonomous underwater vehicle, light-duty trucks, buses, and wearable technology systems.[19][20][21][22] Development of metal hydride fuel cell systems is continuing for military applications, with onboard hydrogen generation and fuel cells up to 5.0 kW.[23][24]
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