Aluminum Air Fuel Cell Becoming Commercially Viable
While aluminum’s attributes in saving energy are highly publicized, perhaps less well known is the material’s potential role in generating energy. Developments started over 25 years ago on an aluminum-air fuel cell are now beginning to see commercial promise in a range of applications from cell phones to PCs to electric vehicles. How does the aluminum-air fuel cell work? What advantages does it have over conventional batteries and portable power sources? Who is producing these products? Read further to learn more.
Warren H. Hunt,
Jr., Ph.D., FASM
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call (202) 862-5119
The aluminum-air fuel cell consists of an aluminum alloy anode, placed in a saline or alkaline electrolyte, which reacts with oxygen from the air or another source. Electricity is produced as the aluminum oxidizes. Physically, a typical cell consists of aluminum alloy plates and a gas diffusion cathode coupled by an electrolyte. When the aluminum alloy is consumed during the electrochemical reaction, a new plate is inserted and the reaction continues. The fuel cell is actually part battery, part fuel cell. Like a battery, the fuel is consumed within the cell. Like a fuel cell, the oxidant, in this case oxygen, is stored outside the cell and provided to the cathode as required
As you might expect, there are some finer points to the process of electricity generation that have needed to be addressed in order for the aluminum-air fuel cell to move from laboratory curiosity to commercial product.
One aspect was related to the aluminum anodes. By nature, aluminum is corrosion resistant, as a result of the adherent aluminum oxide film that forms naturally on its surface. For use in the fuel cell, however, the material needed to be electrochemically active in the presence of the electrolyte. This has been accomplished through alloying the aluminum with tin as well as other proprietary elements.
On the cathode side, delivering the oxygen into the cell has been accomplished through improvements in gas diffusion cathodes, which employ high molecular weight polymers and advanced membrane technology
Another issue was the formation of aluminum hydroxide as a by-product of the reaction, which would form as a gel-like substance on the anode and reduce the reaction rate. Developments here involve the addition of unique additives to the electrolyte that cause the aluminum hydroxide to form in crystalline powdered form, which fall to the bottom of the cell leaving the reaction surface on the anode clear and active.
The development work on metal-air fuel cells in general and the aluminum-air system in particular dates back some 25 years. The driving force was the need for reliable, lightweight power sources for military and space applications, where the weight or limited shelf life of traditional batteries would be unacceptable. Aluminum was a desirable choice for the metal "fuel" since it was lightweight, has a very high energy density, and is recyclable. As a result, successful although expensive fuel cells were designed and constructed. Power system for underwater exploration were developed which delivered ten times more power than the nickel-cadmium batteries it replaced, and also substantially reduced the time taken to recharge a vehicle. Another high performance application was for the Special Forces, in which the battery with a shelf life of greater than 10 years is wrapped in a watertight wrap for shipment and storage, and then activated by the addition of water when the power is required. A company called Fuel Cell Technologies Ltd. in Canada supplied these applications.
Hybrid Electric Vehicles
Today there is an interest in lightweight fuel cells for a range of applications. Probably the one that has garnered the most recent attention is in hybrid electric vehicles (HEVs). According to experts, HEVs will start creeping into the US market (in fact a few are already here) because they use fewer batteries than electric vehicles, recharge themselves on the road, are much friendlier to the environment, and are more fuel efficient than conventional gasoline-powered cars and trucks.
While some of the HEVs will use nickel metal hydride, with weight as well as range being key considerations, a number of other concepts are under consideration as well, including the aluminum-air fuel cell. One company, Alupower Inc. (acquired from Alcan by ENER-TEK in 1994), reports that aluminum-air fuel cells can extend the range of an electric van from 75 km using lead-acid batteries to 300 km. They note that the fuel cells are over seven times more energy dense by weight and occupy less than one-seventh of the space of commercial lead-acid batteries. They are however on the order of ten times more expensive, so the cost-benefit trade-off is important. Watch this area for continuing developments.
Another promising area of application is in supplying portable power for cellular phones and laptop computers, in what has been described as "personal electricity". The aluminum-air fuel cell is said to be up to 75 times more energy dense than lithium-ion fuel cells. In these applications, light weight as well as small package size is important.
One company, Aluminum-Power, Inc., has been focusing their efforts on producing small aluminum-air cells for cellular phones. The company has announced a product that provides adequate power for eight hours of talk time and nearly six days of standby power using an aluminum-air fuel cell they have developed.
The company projects that with optimization they will have a product enabling 25 hours of talk time and 240 hours of stand-by power.
Key to their technology is a sealed "quick-change" cartridge containing the aluminum anode. Once the cartridge is used, it will be able to be recycled curbside with aluminum cans. The planned arrival in 2004 of the third generation (3G) cell phone technology, which is expected to require even more portable power, is expected to be the large growth market for these products.
Due to the scaleable nature of the technology, it can also be used in other larger-scale applications. Aluminum-air fuel cells are expected to find a market among telecommunications and Internet service providers that need fail-safe backup electricity, with computer chip makers that can’t tolerate power outages, at banks to keep ATM systems running, and in supermarkets to protect perishables.
Other potential applications include home power in regions where high power costs or the absence of a power grid prevents the use of electricity as well as fuel for portable generators, to replace diesel generation with a pollution-free alternative. Portable power systems are a particular focus of a company called Voltek, which manufactures a product called "Fuel Pak" that is designed for emergency power, marine, and camping applications as well as for forklift trucks.
What are we talking about dollar-wise? The market for fuel cells in the applications discussed above is growing rapidly. A 1998 report by BCC, Inc. pegs the estimated size of the fuel cell market at $1.3 billion by 2003, growing at a rate of nearly 30% per year. Of this, BCC estimated that the aluminum-air fuel cell market was on the order of $2 million in 1998 and would grow to $25 million by 2003. Other more recent estimates suggest that the market is currently on the order of $1 billion and will grow to $10 billion in the near future, suggesting a more rapid expansion than predicted even by the BCC study.
About the Author
Dr. Warren H. Hunt Jr. is founder and president of Aluminum Consultants Group Inc. Established in 1996, Aluminum Consultants Group Inc. provides its clients with comprehensive support in all aspects of aluminum metallurgy, processes and products. As a network of independent experts with extensive experience in industry, academia, and government, Aluminum Consultants Group, Inc. has excellent capabilities over a broad range of market and technical areas.
Prior to forming Aluminum Consultants, Dr. Hunt had a 19-year career with Alcoa Technical Center, one of the world's largest light metals research laboratories. At Alcoa, he focused on the conceptualization, development, and implementation of new aluminum alloys and metal matrix composites to meet customer needs in a range of markets. At Alcoa, Dr. Hunt served as a core competency leader responsible for integrating materials, product design and manufacturing. In addition, he provided support to Alcoa's manufacturing facilities in aluminum alloy processing and technical marketing.
His efforts have resulted in eight patents in both the alloy and processing fields. He has received recognition for his professional excellence, among them selection as a Fellow of ASM International and two IR 100 awards. Dr. Hunt has lectured extensively in the field of advanced aluminum materials, published more than 35 technical papers, and edited three books.
Dr. Hunt received his BE from Vanderbilt University, and his MS and Ph.D. from Carnegie Mellon University. He serves as an adjunct professor at Case Western Reserve University.