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Metal hydride fuel cells are a subclass of 
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. 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. Additional developments in both the fuel cell stack and system integration enabled a 1.0 kW system, complete with an
Fuel Cell & Hydrogen Energy Association
United States Department of Energy: Hydrogen and Fuel Cells Technologies Office
Fuel Cell Seminar and Energy Exposition
{{Fuel cells Fuel cells
alkaline fuel cell
In chemistry, an alkali (; from the Arabic word , ) is a basic salt of an alkali metal or an alkaline earth metal. An alkali can also be defined as a base that dissolves in water. A solution of a soluble base has a pH greater than 7.0. The a ...
s that have been under research and development
Research and development (R&D or R+D), known in some countries as OKB, experiment and design, is the set of innovative activities undertaken by corporations or governments in developing new services or products. R&D constitutes the first stage ...
, as well as scaled up successfully in operating systems. A notable feature is their ability to chemically bond and store hydrogen within the fuel cell itself.
Characteristics
Metal hydride fuel cells have demonstrated the following characteristics: * The ability to be recharged withelectrical energy
Electrical energy is the energy transferred as electric charges move between points with different electric potential, that is, as they move across a voltage, potential difference. As electric potential is lost or gained, work is done changing the ...
(similar to NiMH batteries)
* Operating at low temperatures (down to −20 °C)
* Fast "cold start" properties
* Ability to operate for limited periods of time with no external hydrogen
Hydrogen is a chemical element; it has chemical symbol, symbol H and atomic number 1. It is the lightest and abundance of the chemical elements, most abundant chemical element in the universe, constituting about 75% of all baryon, normal matter ...
fuel source, enabling "hot swapping" of fuel canisters
Performance
Electrode
An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or a gas). In electrochemical cells, electrodes are essential parts that can consist of a varie ...
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. The scaling up of electrode active areas also provided capabilities to develop higher power fuel cell stacks, each with 1500 Watts of power. Metal hydride fuel cells have achieved a current density
In electromagnetism, current density is the amount of charge per unit time that flows through a unit area of a chosen cross section. The current density vector is defined as a vector whose magnitude is the electric current per cross-sectional ...
of 250 mA/cm2. To test durability, fuel cell stacks were successfully operated for more than 7000 hours.
Operating systems and applications
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. 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. Additional developments in both the fuel cell stack and system integration enabled a 1.0 kW system, complete with an inverter
A power inverter, inverter, or invertor is a power electronic device or circuitry that changes direct current (DC) to alternating current (AC). The resulting AC frequency obtained depends on the particular device employed. Inverters do the op ...
and onboard hydrogen storage
Several methods exist for storing hydrogen. These include mechanical approaches such as using high pressures and low temperatures, or employing chemical compounds that release H2 upon demand. While large amounts of hydrogen are produced by variou ...
using metal hydride storage canisters, to be operated and demonstrated in public. 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. In tandem with product development, there was also a focus on developing capabilities for manufacturing and testing. Metal hydride fuel cell systems have been integrated into microgrid
A microgrid is a local electrical grid with defined electrical boundaries, acting as a single and controllable entity. It is able to operate in grid-connected and off-grid modes.
systems at military base
A military base is a facility directly owned and operated by or for the military or one of its branches that shelters military equipment and personnel, and facilitates training and operations. A military base always provides accommodations for ...
s for testing and evaluation. Despite challenges, the military maintains an active interest in fuel cells for a broad range of applications, including unmanned aerial vehicles
An unmanned aerial vehicle (UAV) or unmanned aircraft system (UAS), commonly known as a drone, is an aircraft with no human pilot, crew, or passengers onboard, but rather is controlled remotely or is autonomous.De Gruyter Handbook of Dron ...
, autonomous underwater vehicle
An autonomous underwater vehicle (AUV) is a robot that travels underwater without requiring continuous input from an operator. AUVs constitute part of a larger group of undersea systems known as unmanned underwater vehicles, a classification tha ...
, light-duty trucks
A truck or lorry is a motor vehicle designed to transport freight, carry specialized payloads, or perform other utilitarian work. Trucks vary greatly in size, power, and configuration, but the vast majority feature body-on-frame construction ...
, buses
A bus (contracted from omnibus, with variants multibus, motorbus, autobus, etc.) is a motor vehicle that carries significantly more passengers than an average car or van, but fewer than the average rail transport. It is most commonly used ...
, and wearable technology
Wearable technology is any technology that is designed to be used while worn. Common types of wearable technology include smartwatches, fitness trackers, and smartglasses. Wearable electronic devices are often close to or on the surface of the s ...
systems. Development of metal hydride fuel cell systems is continuing for military applications, with onboard hydrogen generation and fuel cells up to 5.0 kW.
See also
*Glossary of fuel cell terms
The Glossary of fuel cell terms lists the definitions of many terms used within the fuel cell industry. The terms in this fuel cell glossary may be used by fuel cell industry associations, in education material and fuel cell codes and standards to ...
* Hydrogen technologies
Hydrogen technologies are technologies that relate to the production and use of hydrogen as a part hydrogen economy. Hydrogen technologies are applicable for many uses.
Some hydrogen technologies are carbon neutral and could have a role in pre ...
References
External links
Fuel Cell & Hydrogen Energy Association
United States Department of Energy: Hydrogen and Fuel Cells Technologies Office
Fuel Cell Seminar and Energy Exposition
{{Fuel cells Fuel cells