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Will fuel cells power an automotive revolution?
By Mark Allan Gottschalk -- Design News, June 22, 1998
The wait for a breakthrough in battery technology to power future electric vehicles is over, because electric cars of the 21st century won't need them. They are going to run on fuel cells.
At least that's the view of many in the automotive world. After several decades of work by industry, universities, and research facilities, they say, the automotive fuel cell has finally passed that critical point in any technology's development that separates a laboratory curiosity from the potential of high-volume production.
"This isn't a trend, it's a boom " says Robert Rose, Executive Director of Fuel Cells 2000, a private, non-profit Washington D.C.-based educational organization.
If he and others are right, the transition from internal-combustion (IC)-powered vehicles to fuel cell/electric vehicles over the next two decades might possibly be the most significant change in the automobile since Henry Ford introduced Carl Benz's invention to the assembly line.
Don't believe it? Consider the evidence:
- Early last year, Daimler-Benz stunned the automotive world by investing $145 million in the largest fuel cell manufacturer, Ballard Power Systems (Vancouver, BC). The two firms jointly pumped $240 million into the launch of two new companies, DBB Fuel Cell Engines, and Ballard Automotive Inc, and announced that they would be producing 100,000 fuel cell engines a year by 2005.
- In September, Mercedes-Benz rolled out its third-generation fuel cell automobile, NECAR 3, based on the company's compact A Class car.
- Chrysler, recently acquired by Daimler-Benz, has teamed with Arthur D. Little to create an operational prototype gasoline-fueled fuel cell vehicle by 1999. The company also announced that by 2015 fuel cells could be the primary source of power for the company's Concorde/Intrepid class of cars.
(There was no indication at press time that the merger with Daimler would affect Chrysler's fuel-cell programs.)
- In December 1997, Ford bought into the Daimler-Benz/Ballard alliance, committing $420 million to the arrangement.
- General Motors unveiled an advanced model of a fuel cell drivetrain this January, and announced its intent to have a production-ready fuel cell vehicle by 2004.
- Toyota has been conducting road tests with two versions of its fuel cell electric vehicle (FCEV), which is based on the RAV4L sport utility vehicle. One stores hydrogen onboard in a metal hydride "fuel tank;" the other derives its hydrogen from methanol and has a 310-mile range.
- Volkswagen and Volvo expect to have a methanol-fueled fuel cell car based on the "Golf" platform by 1999.
To imagine that fuel cells, a technology which had languished for nearly 160 years, could significantly impact the future of automotive transportation and possibly displace what has been the overwhelmingly dominant method of vehicle propulsion for the past century seems almost absurd. Amazingly, the car companies seem to be as surprised at fuel cells' sudden popularity as anyone else.
"Sudden is a good way to put it," says Bradford Bates, manager of alternative power source technology at Ford Research Lab. "I think it was only 18 months ago that I was telling people I didn't think my grandchildren were going to be able to buy a fuel cell car. Today, it would be quite surprising if they couldn't buy one."
What is fueling this phenomenon? At the foundation are the same factors that prompted research into developing battery-powered electric vehicles: the need to cut vehicle emissions, improve fuel economy, and--don't discount this--meet increasingly stringent U.S. government standards. "We wouldn't be talking about any of these technologies if the California Air Resources board had not adopted their ULEV and ZEV emission standards in 1990," says Rose.
But in this game, fuel-cell electric vehicles have something going for them that battery-powered vehicles don't. They look like internal combustion cars, perform like internal combustion cars, have superior range to internal combustion cars, and have the potential for being refueled just like internal combustion cars.
While all fuel cells ultimately require hydrogen and oxygen for fuel, hydrogen can be extracted from hydrocarbon fuels by an on-board reformer, allowing a fuel cell vehicle to run on methanol--as with Mercedes-Benz' and Toyota's prototypes--or even off gasoline, as Chrysler is proposing.
More specifically, compared to both battery-powered vehicles and internal combustion vehicles, fuel cells offer advantages such as:
- Energy density. "There are many factors, but fuel cells should still end up having two to three times the energy and power density of battery-powered vehicles," says Rhett Ross, vice president of product development at Energy Partners, a fuel cell manufacturer. A lithium ion battery has on the order of 120W hours per kg; methanol, even after processing for use in the fuel cell, has more than 2,000W hours per kg.
- Zero emission. When powered by pure hydrogen, fuel cells produce water as their primary "emission." By contrast, battery-powered electric vehicles generate significant CO(sub2) emissions in the energy-production process. Fuel cell vehicles using reformed methanol as fuel do have some emissions to control, but should still easily meet ULEV and ZEV standards.
- Range. Superior energy density means superior range. When powered by hydrocarbon fuels, a fuel cell will even beat current IC automobiles. "Fuel cells offer between a factor of two and three improvement in overall fuel economy," says Byron McCormick, executive director of General Motors Global Alternative Propulsion Center.
- Packaging. Batteries show little promise of being reduced in size much from where they are now. A current 50 kW fuel cell stack could be placed down the floor tunnel of an existing midsize sedan, leaving room for six passengers and luggage, says Dr. Chris Borroni-Bird, Chrysler advanced technologies specialist. And they have the potential of being optimized significantly more.
- Simplicity. "Compared to the drivetrain in today's cars, there are fewer parts, fewer high-tolerance parts, the parts are easier to make, and they are made from materials that costs less," says Bates.
- Performance. "The fuel cell stack is finally at the point where it has adequate power density and adequate performance to really make an all-out performance car," claims McCormick.
- Cost. "Ten years ago, fuel cells were 1,000 times too expensive and now they're about ten times too costly," says Borroni-Bird. He estimates that additional engineering work might cut the cost by a factor of three to five, and volume production will bring it down the rest of the way.
- Refuelability. This is the fuel cell's ace in the hole. There is talk about reducing the charging time for battery-powered cars to 15 or 20 minutes. A methanol- or gasoline-fueled fuel-cell car will spend no more time in the gas station than today's cars.
Critical breakthroughs. If all these potential advantages sound too good to be true, it's because for the last 160 years they were. Sir William Grove invented the fuel cell in 1839, long before the common use of electricity. Little happened with them for more than a century until NASA incorporated fuel cells into its Gemini and Apollo space capsules. It took decades of engineering work to arrive at that point.
As late as 1990, a Ballard Mark I or Mark II fuel cell would produce about 2.5 kW peak output on hydrogen and oxygen, and 1 kW on air. If scaled up to the minimum 50 kW size required for an automobile, it would be larger than the car.
Fuel cells work by combining hydrogen and oxygen into water, producing electricity in the process. There are five basic types of fuel cells, differentiated solely by the type of electrolyte separating the hydrogen from the oxygen. However, the only technology being considered for automobiles is Proton Exchange Membrane, or PEM.
For automotive applications, PEM offers several advantages: They are low temperature--less than 80C--for quick startup, they contain water instead of caustic acids or bases, they respond well to transient loads, they scale well to different sizes, and they are relatively simple to mass manufacture.
"You basically have a piece of plastic--think of Saran wrap--that you put between a couple of pieces of carbon paper," says Henry Voss, manager of portable power systems development at Ballard Power Systems, "and you sandwich that between some plates that have channels carved in them to distribute the gases which are going to react."
Despite its claimed advantages, PEM's current dominant position is somewhat surprising. As late as 1994 a Department of Energy handbook on fuel cells didn't even contain a chapter on PEM technology. Why? At the time, they were prohibitively expensive. For a catalyst, PEM cells use one of the most costly metals on earth: platinum.
"Five to seven years ago, the average platinum loading was 4 to 8 milligrams per square centimeter," says Energy Partners' Ross. "A stack with a hundred cells and each cell having 500 square centimeters of surface area would really cost a bundle."
In fact, researchers at Los Alamos National Laboratory calculated that it would have required $30,000 worth of platinum for a PEM fuel cell sufficient to power a typical passenger car.
Through the 1980s and early 1990s these researchers developed ways to reduce the platinum loading to as little as 0.25 mg/sq cm, dropping the cost of the platinum needed to just a few hundred dollars.
The old method of applying catalyst required taking the processed platinum, placing it on a substrate, and then taking the substrate and pressing it to the membrane. To ensure good coverage, more platinum was used then actually needed. "The only place you need platinum catalyst is where it's in contact with the membrane," says Ross. "Any catalyst which is not in contact with the membrane is simply providing electrical conductivity, and other materials can do that cheaper."
The method developed at Los Alamos involves forming the film as an ink that is spread and cured on a film release blank. The cured film is then transferred to the electrolyte membrane and hot pressed into the surface to form a catalyst layer having a controlled thickness and distribution. Other companies have developed their own proprietary methods akin to electroplating. The net result: platinum requirements have plummeted by as much as 90%.
At the same time, power density has increased more than tenfold. A Ballard fuel cell that output 100W/(liter) in 1989 today exceeds 1,300 W/(liter). "One thousand watts per liter is considered the threshold for automotive applications," says Voss, "We passed that point just a couple of years ago."
The reformation factor. Though all fuel cells require hydrogen to operate, a battle is being waged over the source of that hydrogen. Pure hydrogen offers the allure of simplicity and the complete absence of emissions, whereas hydrocarbon-based fuels, such as methanol or ethanol, offer easier storage and distribution at the cost of some additional emission controls and some lost efficiency in the reformation process needed to extract the hydrogen.
Hydrogen gas can be stored by compressing it into tanks. This is not only relatively inconvenient to refuel, the storage density of compressed hydrogen isn't that high. As an alternative, the hydrogen can be absorbed into a metal hydride. Toyota, for example, has developed a hydrogen-absorbing titanium alloy with a cube-shaped atomic structure that can hold and release twice as much hydrogen as any previously known material. The company claims that 100 kg of the alloy can store two kilograms of hydrogen, the equivalent of 20,000(liter) of gaseous hydrogen. Surprisingly, this is 30 to 35% more hydrogen per volume than a tank of liquid hydrogen--which must be kept chilled to-253C--and five times that of a tank of compressed gas.
Ironically, the very fuel jeopardized by the fuel cell--gasoline--may prove to be the technology's savior (see "Fossil-fueled fuel cell"). "We believe that the major advancement which will make fuel cells viable is the ability to use gasoline," says Chrysler's Borroni-Bird. "It will be a bridge. If you try to introduce a new fuel such as hydrogen or methanol at the same time as you introduce a new power train, you set yourself up for failure."
The company believes it can get a fuel cell car to market ten years sooner by taking this approach. Envisioned is a family car that could get up to 80 mpg, accelerate to 60 mph under seven seconds, and cruise nearly 400 miles between fuel stops with a tank less than two-thirds the size required today. Chrysler's approach is, in actuality, fuel neutral since it can also use methanol or ethanol. "Gasoline is the most difficult fuel to convert," says Borroni-Bird, "and if we can run on gasoline, we know we can run on any other fueled being proposed."
Mercedes-Benz is placing its bet on methanol. This past September the company unveiled NECAR 3, a modified A-class compact car that uses a reformer to provide hydrogen for its Ballard fuel cell. Unlike its predecessors, the demonstration vehicle requires no batteries to buffer the fuel cell's output. Ninety percent of the system's power is available in just two seconds, and it has a range of 250 miles from 10.5(liter) of methanol (remember, methanol has half the energy content of gasoline).
NECAR 3 is Mercedes-Benz' third fuel cell automobile in three years. "In 1994, the fuel cells in NECAR 1 took up most of the cargo space in a delivery van," says Fuel Cells 2000's Rose. "And now they've got it and the drivetrain engineered to fit in a compact car."
General Motors is in the methanol camp as well. They have no prototype vehicles, but are studying laboratory systems based on GM-designed fuel cells and a GM-designed fuel processor. They've shown drawings of a concept vehicle based on the current EV1. Unlike Mercedes-Benz' NECAR 3, the concept car appears to have a substantial battery pack on-board. Given the company's head start with the low-production EV1, they should be able to meet their announced goal of a production-ready prototype by 2004.
The biggest obstacles lie beyond the prototype, when engineers must get into the details we take for granted in today's cars. "The challenge lies in making the fuel cell system consumer acceptable," says McCormick. "You've got to be able to start it in February in Fargo, North Dakota."
Ford arrived a little later to the fuel cell scene than its competitors. But they've caught up quickly as a result of their joint venture with Ballard and Mercedes-Benz.
The company's plan is to create a fuel cell version of their P2000 concept car. P2000 is actually a family of cars with different power trains. The objective was to create a Taurus-size car weighing just 2,000 lbs, that had 2 sq m of frontal area, and a 0.2 drag coefficient. Engineers began with the Contour/Mystique platform, lengthened and widened it a bit, and fastened aluminum sheet to it with titanium fasteners.
Ford has a 50 kW fuel cell, developed by International Fuel Cells (South Windsor, CT), running in its lab. The company judges it sufficient for the P2000, but about half what would be needed for an average car today. They've made no commitment to a specific fuel, but seemed to be taking a look-and-see attitude. Ultimately, it's expected that they will use fuel cells that come out of their partnership with Ballard and Mercedes-Benz.
Engineering opportunities. While the outlook for fuel cells could not be more optimistic, there is still a tremendous amount of engineering work that needs to be done. Platinum catalyst quantities, for instance, could be further dropped to levels found in today's catalytic converters. Improved membrane materials could significantly increase efficiency.
Fuel Cells 2000's Rose believes that the key issues aren't even in the fuel stacks themselves. "The obstacles are just as big in the balance of the system," he says. There are pumps to be designed, complexities of the fuel system to be figured out, electronic control systems to be developed, carbon monoxide sensors to be created.
In vehicles that use fuel processors, techniques must be developed to separate the hydrogen from the impurities and, for gasoline fueled vehicles, a filter developed to strip out sulfur compounds. In addition, entirely new manufacturing processes and their assembly lines need to be created--no small feat for an industry that currently pumps out millions of highly complicated automobiles every year.
If there is an easy part, it might be the rest of vehicle, "which is really just an electric vehicle," says Bates from Ford Research Lab. "And we've been doing that for a years with our electric Ranger {pickup truck}."
Most experts believe the first fuel cell vehicles will actually be hybrids that use a small battery of some sort to start the system and capture energy from regenerative braking.
But no matter the ultimate technology used, engineers have to stay focused on the primary objective: making automobiles that are safe, perform well, refuel easily, travel further on less fuel, and, hopefully, emit nearly zero emissions.
"We have to make sure that when a person walks into a showroom and looks at a fuel cell vehicle and then looks at a internal combustion engine vehicle, it's a wash," says McCormick. "They can't be thinking, I've got to pay thousands of dollars to get clean air."
How a PEM fuel cell works
PEM fuel cells are well-suited for automobiles because of their high power density and low operating temperature (&100C), which allows quick startup. Also, they can be run with hydrogen derived from fuels such as methanol or gasoline. A Polymer Electrode Membrane (PEM) fuel cell consists of a cathode and anode separated by a polymer-membrane electrolyte. One side of each electrode is coated with platinum catalyst. The catalyst causes the hydrogen to separate into free electrons and protons at the anode. The electrons form the cell's electrical output. The protons migrate through the membrane to the cathode, where the catalyst causes them to combine with oxygen to form water and heat.
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