Personal Power Takes A Walk
Manportable systems may soon provide an alternative to batteries.
The Power Knight system uses alkaline-based fuel cells. Unlike the more common proton exchange membrane (PEM) fuel cells being developed for personal electronics, Power Knight’s alkaline cells do not use expensive materials such as platinum or palladium in their electrolytes. Alkaline-based devices also are less complicated because they do not require pumps to move the electrolyte through the catalyst to generate power.
A lightweight fuel cell technology may soon be powering warfighters’ battlefield electronic equipment. Currently being tested by
Mass-produced, commercially viable fuel cells only now are becoming available. The technology behind the Power Knight military fuel cell is among the first of these personal power devices to bridge the gap between military and civilian markets. Developed and manufactured by Medis Technologies Limited,
Although many companies and research organizations have been working on fuel cells designed to power electronics (SIGNAL Magazine, June 2001), most of these technologies are still experimental and years away from production, contends Jacob S. Weiss, Medis’ president. The key difference between the Power Knight and most other manportable fuel cells is in its architecture. Many small fuel cells use proton exchange membrane (PEM) technology (see box, page 81). But Weiss contends that these devices face cost restrictions because their membranes must be coated with expensive platinum or palladium to achieve desired performance.
Company researchers instead chose to develop an alkaline-based fuel cell. Weiss explains that alkaline cells have a major advantage over PEM-based systems because they do not require expensive noble metals in their membranes. The Power Knight system has no noble metals on its cathode, and its anode currently has minimal amounts of noble metals. Weiss notes that the company soon will eliminate the need for noble metals entirely. “You can’t do that with a PEM system,” he says.
Another factor behind choosing an alkaline-based system was safety. The fuel of choice for PEM-based cells is either methanol or ethanol. Both of these fuels are flammable at relatively low temperatures and present hazards for military and civilian use.
Weiss relates that when Medis scientists decided to develop an alkaline-based fuel cell, they realized that a different type of fuel was necessary to achieve high-energy performance. After some consideration, they chose borohydride. However, there are challenges associated with the fuel. “It’s got an extremely high energy potential, but it’s very unstable,” Weiss explains. Company researchers stabilized borohydride into a proprietary fuel consisting of a borohydride base with other substances and alkaline components.
Because the company chose a different approach, Weiss is confident that Medis is well-positioned with its alkaline-based technology. “Everyone else is doing PEM, ethanol or hydrogen. They are trying to tweak existing concepts. They have patents that are nuances of the various means a lot of other people are developing,” he says. This close grouping of similar patents very easily could lead to many legal challenges between competing firms. In contrast, he claims that Medis’ alkaline-based system is unique.
The company’s technology has drawn interest from several nations’ armed forces. Medis fuel cells have provided up to 800 watts of power to a platform for an Israeli unmanned aerial vehicle program led by Israel Aerospace Industries Incorporated. Medis also is working with General Dynamics to develop military fuel cells for the U.S. Defense Department. Power Knight is a spinoff of the technology the firm is developing for General Dynamics as part of a Defense Department competition for a manportable power pack.
The requirements for the competition were daunting. Weiss explains that the
By comparison, lithium ion batteries and other similar technologies can provide a maximum of 190 to 200 watt-hours per kilogram. The Power Knight system consists of three fuel cells. To achieve the 200-watt peak, it was necessary to use a battery. However, he adds that the constant 20-watt power supply is provided by the fuel cells. The battery provides about 5 percent of the system’s overall electrical power and takes up 1.1 kilos of the device’s weight. The remaining 3 kilos and 95 percent of the Power Knight’s energy come from the three fuel cells. In its current version, Power Knight can provide a soldier’s electronics with 20 watts of continuous power for 72 hours.
Weiss is confident that Medis and General Dynamics will come very close to achieving the government specifications. He believes that the Power Knight will be among the top systems selected with the possibility for further work with the
Medis also is supplying the Power Knight to European and Israeli military programs. Weiss notes that his firm is working with Elbit Systems to provide power systems for
European power requirements for its soldier kit are more modest than those of the
Besides pinning down military contracts, Medis is moving into commercial markets. The company established production facilities in
Weiss sees military contracts as a key anchor for the company’s future. However, he stresses that the firm’s primary business model focuses on commercial markets. Entire industries and applications such as movies, books and music are now being sold on handheld devices. “There’s no phone that anyone’s selling that doesn’t give you an iPod type of function,” he maintains.
All of these new functions consume energy. Because consumers rely on these devices to remain running, a more reliable power source is necessary. Weiss relates that many mobile device users are moving toward Google’s advertising approach. “The way that mobile operators made their money until now was selling time. But because of the severe competition in the mobile environment, that’s been commoditized. So their margins are basically going down to zero,” he says.
To obtain revenue from their services, mobile device operators would charge for downloading songs or ring tones. But this approach will not work anymore; he indicates that the new frontier is selling advertising over wireless devices. But to sell advertising means that data must be constantly pushed to the user, which uses power. “All of this stuff is blowing through your battery and sitting on an inverted pyramid. At the bottom of that pyramid is a lithium ion battery that basically has minimal growth potential unless you add lithium, and then it’s a bomb,” he remarks.
Weiss explains that the solution to support all of these wireless functions is to provide a safe source of portable power. He maintains that Medis’ fuel cell is the only viable commercial system available to meet these needs. “Cost is a big issue. No one is going to pay any amount just because the word ‘fuel cell’ appears on it. We’re the only ones standing, and for better or worse, we’ll have to create the market by ourselves,” he says.
Fuel Cells 101
Fuel cells generate electricity through a chemical reaction. These devices have two electrodes—one positive cathode and one negative anode. The reactions that produce electricity occur at the electrodes. All fuel cells have an electrolyte to carry electrically charged particles between the electrodes and a catalyst to speed the reactions at the electrodes.
The key fuel for fuel cells is hydrogen, either in its pure form or in a fuel such as methanol. Fuel cells also need oxygen as part of the energy conversion process. As long as a fuel cell is supplied with hydrogen and oxygen, it will generate power. A major appeal of fuel cells is that they provide energy while creating little or no pollution. Any byproducts they do produce are mostly in the form of water vapor. Fuel cells also are more efficient at extracting energy from fuel.
Fuel cells fall into five groups based on the type of electrolyte. These are alkaline, molten carbonate, phosphoric acid, proton exchange membrane (PEM) and solid oxide. The choice of electrolyte falls to the type of platform and mission intended for the fuel cell. The choice of electrolyte also affects electrode design and the materials used to make them.
Alkaline fuel cells were used in the Apollo spacecraft to provide electricity and drinking water. These fuel cells compress hydrogen and oxygen to operate. They generally use a potassium hydroxide solution in water as an electrolyte. Many types of alkaline fuel cells require expensive platinum electrode catalysts.
Molten carbonate fuel cells use high-temperature salt carbonate compounds such as sodium or magnesium and an electrolyte. Operating at temperatures up to 650 degrees Celsius, these cell types can generate power levels in excess of 2 megawatts. Their nickel electrode catalysts are inexpensive compared to other types of fuel cells, but their high temperatures limit their use.
Phosphoric acid fuel cells use the substance as an electrolyte. Current phosphoric acid fuel cells have power outputs up to 200 kilowatts, and 11- megawatt units have been tested. However, phosphoric acid fuel cells require platinum electrode-catalysts and their internal components must withstand the corrosive acid.
PEM fuel cells use a thin, permeable polymer sheet as an electrolyte. The solid, flexible electrolyte will not leak or crack, making it suitable for vehicle and personal electronics applications. But PEM fuel cells require purified fuels, and a platinum catalyst must be used on both sides of the membrane.
Solid oxide fuel cells use a hard ceramic compound of metal oxides such as calcium or zirconium as electrolytes. These fuel cells can produce up to 100 kilowatts of power, but they operate at very high temperatures of about 1,000 degrees Celsius. The amount of insulation required by their high temperature means they are usually very large.