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]
A fuel cell is an electrochemical cell that converts the chemical energy of a fuel and an oxidizing agent into electricity through a pair of redox reactions. Fuel cells are different from most batteries in requiring a continuous source of fuel and oxygen to sustain the chemical reaction, whereas in a battery the chemical energy usually comes from substances that are already present in the battery. Fuel cells can produce electricity continuously for as long as fuel and oxygen are supplied.
Energy storage is the capture of energy produced at one time for use at a later time to reduce imbalances between energy demand and energy production. A device that stores energy is generally called an accumulator or battery. Energy comes in multiple forms including radiation, chemical, gravitational potential, electrical potential, electricity, elevated temperature, latent heat and kinetic. Energy storage involves converting energy from forms that are difficult to store to more conveniently or economically storable forms.
A nickel metal hydride battery is a type of rechargeable battery. The chemical reaction at the positive electrode is similar to that of the nickel–cadmium cell (NiCd), with both using nickel oxide hydroxide (NiOOH). However, the negative electrodes use a hydrogen-absorbing alloy instead of cadmium. NiMH batteries can have two to three times the capacity of NiCd batteries of the same size, with significantly higher energy density, although much less than lithium-ion batteries.
Zinc–air batteries (non-rechargeable), and zinc–air fuel cells are metal–air batteries powered by oxidizing zinc with oxygen from the air. These batteries have high energy densities and are relatively inexpensive to produce. Sizes range from very small button cells for hearing aids, larger batteries used in film cameras that previously used mercury batteries, to very large batteries used for electric vehicle propulsion and grid-scale energy storage.
A flow battery, or redox flow battery, is a type of electrochemical cell where chemical energy is provided by two chemical components dissolved in liquids that are pumped through the system on separate sides of a membrane. Ion transfer inside the cell occurs through the membrane while both liquids circulate in their own respective space. Cell voltage is chemically determined by the Nernst equation and ranges, in practical applications, from 1.0 to 2.43 volts. The energy capacity is a function of the electrolyte volume and the power is a function of the surface area of the electrodes.
Energy Conversion Devices (ECD) was an American photovoltaics manufacturer of thin-film solar cells made of amorphous silicon used in flexible laminates and in building-integrated photovoltaics. The company was also a manufacturer of rechargeable batteries and other renewable energy related products. ECD was headquartered in Rochester Hills, Michigan.
Direct borohydride fuel cells (DBFCs) are a subcategory of alkaline fuel cells which are directly fed by sodium borohydride or potassium borohydride as a fuel and either air/oxygen or hydrogen peroxide as the oxidant. DBFCs are relatively new types of fuel cells which are currently in the developmental stage and are attractive due to their high operating potential in relation to other type of fuel cells. Recently, DBFCs that rival proton-exchange membrane fuel cells (PEMFCs) in peak power but operating at double the voltage have been reported.
Molten-salt batteries are a class of battery that uses molten salts as an electrolyte and offers both a high energy density and a high power density. Traditional non-rechargeable thermal batteries can be stored in their solid state at room temperature for long periods of time before being activated by heating. Rechargeable liquid-metal batteries are used for industrial power backup, special electric vehicles and for grid energy storage, to balance out intermittent renewable power sources such as solar panels and wind turbines.
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 various industries, it is mostly consumed at the site of production, notably for the synthesis of ammonia. For many years hydrogen has been stored as compressed gas or cryogenic liquid, and transported as such in cylinders, tubes, and cryogenic tanks for use in industry or as propellant in space programs. Interest in using hydrogen for on-board storage of energy in zero-emissions vehicles is motivating the development of new methods of storage, more adapted to this new application. The overarching challenge is the very low boiling point of H2: it boils around 20.268 K (−252.882 °C or −423.188 °F). Achieving such low temperatures requires expending significant energy.
Nickel(II) hydroxide is the inorganic compound with the formula Ni(OH)2. It is a lime-green solid that dissolves with decomposition in ammonia and amines and is attacked by acids. It is electroactive, being converted to the Ni(III) oxy-hydroxide, leading to widespread applications in rechargeable batteries.
Microbial fuel cell (MFC) is a type of bioelectrochemical fuel cell system also known as micro fuel cell that generates electric current by diverting electrons produced from the microbial oxidation of reduced compounds on the anode to oxidized compounds such as oxygen on the cathode through an external electrical circuit. MFCs produce electricity by using the electrons derived from biochemical reactions catalyzed by bacteria. MFCs can be grouped into two general categories: mediated and unmediated. The first MFCs, demonstrated in the early 20th century, used a mediator: a chemical that transfers electrons from the bacteria in the cell to the anode. Unmediated MFCs emerged in the 1970s; in this type of MFC the bacteria typically have electrochemically active redox proteins such as cytochromes on their outer membrane that can transfer electrons directly to the anode. In the 21st century MFCs have started to find commercial use in wastewater treatment.
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.
A nickel–hydrogen battery (NiH2 or Ni–H2) is a rechargeable electrochemical power source based on nickel and hydrogen. It differs from a nickel–metal hydride (NiMH) battery by the use of hydrogen in gaseous form, stored in a pressurized cell at up to 1200 psi (82.7 bar) pressure. The nickel–hydrogen battery was patented on February 25, 1971 by Alexandr Ilich Kloss and Boris Ioselevich Tsenter in the United States.
A metal–air electrochemical cell is an electrochemical cell that uses an anode made from pure metal and an external cathode of ambient air, typically with an aqueous or aprotic electrolyte.
A hydride compressor is a hydrogen compressor based on metal hydrides with absorption of hydrogen at low pressure, releasing heat, and desorption of hydrogen at high pressure, absorbing heat, by raising the temperature with an external heat source like a heated waterbed or electric coil.
A solar fuel is a synthetic chemical fuel produced from solar energy. Solar fuels can be produced through photochemical, photobiological, and electrochemical reactions.
Proton exchange membrane(PEM) electrolysis is the electrolysis of water in a cell equipped with a solid polymer electrolyte (SPE) that is responsible for the conduction of protons, separation of product gases, and electrical insulation of the electrodes. The PEM electrolyzer was introduced to overcome the issues of partial load, low current density, and low pressure operation currently plaguing the alkaline electrolyzer. It involves a proton-exchange membrane.
Hydrogenics is a developer and manufacturer of hydrogen generation and fuel cell products based on water electrolysis and proton-exchange membrane (PEM) technology. Hydrogenics is divided into two business units: OnSite Generation and Power Systems. Onsite Generation is headquartered in Oevel, Belgium and had 73 full-time employees as of December 2013. Power Systems is based in Mississauga, Ontario, Canada, with a satellite facility in Gladbeck, Germany. It had 62 full-time employees as of December 2013. Hydrogenics maintains operations in Belgium, Canada and Germany with satellite offices in the United States, Indonesia, Malaysia and Russia.
Dioxide Materials was founded in 2009 in Champaign, Illinois, and is now headquartered in Boca Raton, Florida. Its main business is to develop technology to lower the world's carbon footprint. Dioxide Materials is developing technology to convert carbon dioxide, water and renewable energy into carbon-neutral gasoline (petrol) or jet fuel. Applications include CO2 recycling, sustainable fuels production and reducing curtailment of renewable energy(i.e. renewable energy that could not be used by the grid).
The Iron Redox Flow Battery (IRFB), also known as Iron Salt Battery (ISB), stores and releases energy through the electrochemical reaction of iron salt. This type of battery belongs to the class of redox-flow batteries (RFB), which are alternative solutions to Lithium-Ion Batteries (LIB) for stationary applications. The IRFB can achieve up to 70% round trip energy efficiency. In comparison, other long duration storage technologies such as pumped hydro energy storage provide around 80% round trip energy efficiency.
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