"The most important unresolved issue with fuel cell vehicles is not the fuel cell -- it's the fuel," said Thomas Moore, vice president at DaimlerChrysler's Liberty & Technical Affairs R&D group. Since fuel cells typically operate on hydrogen, there are still major concerns about infrastructure, on-board storage and safety issues. Indeed, because of these concerns, many of the automakers are planning on using reformers to transform fossil fuels like gasoline or methanol into hydrogen so they can have fuel cell vehicles in dealer's showrooms within a couple of years, at least in limited quantities.

Recently, DaimlerChrysler and Millennium Cell, Inc. unveiled an alternative solution to the hydrogen logistics, safety and storage challenges with its Natrium concept vehicle based on a Chrysler Town and Country minivan. The Natrium features Millennium Cell's Hydrogen on Demand fuel system supplying gaseous hydrogen to a Ballard/XCELLSiS PEM (proton exchange membrane) fuel cell. The fuel used in the Hydrogen on Demand system is sodium borohydride ([NaBH.sub.4]), thus the name Natrium (Latin for sodium). The [NaBH.sub.4] dissolved in water passes through a catalyst chamber releasing a stream of pure hydrogen with sodium borate ([NaBO.sub.2]) as a byproduct. The reaction is: [NaBH.sub.4] + [2H.sub.20] [right arrow] [4H.sub.2] + [NaBO.sub.2]

Note that half of the hydrogen comes from the [NaBH.sub.4] and the other half comes from the water. This pure hydrogen is combined with oxygen in the air to produce electricity.

Hydrogen from the borohydride is released during a single pass through the Hydrogen on Demand catalyst chamber with a fuel pump controlling the generation. Hydrogen flow is controlled by turning the pump on and off. When hydrogen is not needed, the pump is shut off to isolate the catalyst from the fuel. Finer control of the hydrogen generation rate is done by increasing and decreasing the pumping rate. After passing through a gas-liquid separator, [NaBO.sub.2] byproduct goes to a spent fuel tank while the hydrogen gas and steam can pass through an optional heat exchanger! coolant system if humidity control is needed.

The process occurs at low pressure and at room temperature. The proprietary catalyst can be reused many times.

The hydrogen could also be used to fuel an internal combustion engine. Millennium Cell has already shown this application in two Ford Crown Victorias. One was originally equipped with an internal combustion engine running on compressed and the other was a New York City taxi with its engine modified to run on gaseous hydrogen.

According to DaimlerChrysler and Millennium Cell, the safety and storage issues with [NaBH.sub.4] are diminished because it can be handled in inflammable dry powder form. The [NaBH.sub.4] produces about the same amount of energy per equivalent gallon as gasoline. Thus, the Natrium has a range of 300 miles with its fuel storage and processing system completely packaged under the minivan's floor without any intrusion into the cabin so interior capacity is not reduced. The tanks for the [NaBH.sub.4] can be made of the same plastic materials and essentially the same size as today's gasoline tanks. Three hundred miles is significantly better than most other of today's fuel cell concept vehicles.

While not yet completely resolved, proponents of boron-based fuels, believe that infrastructure problems are less challenging than with other fuels considered for fuel cell vehicles. Some technical issues remain with the recycling of the borax, and the fuel distribution method is undecided.

DCX and Millennium Cell also tout the environmental benefits of boron-based fuels. Not using fossil fuels, no greenhouse gas or smog-forming compounds are produced during the generation of hydrogen. Another advantage of Hydrogen on Demand over reforming is that no carbon monoxide is involved to poison the fuel cell.

Sodium borohydride is available in large supplies in the U.S., including huge deposits in California's Mojave Desert. The sodium boride or borax byproduct, a common detergent ingredient, is also environmentally friendly Not insignificant is that [NaBO.sub.2] can be recycled back into new [NaBH.sub.4] fuel to provide potentially endless supply of fuel.

The Chrysler Town & Country Natrium features a 35 kW (47 hp) Siemens a.c. electric motor driving the front wheels and has regenerative braking to increase fuel economy, which is 30 mpg gasoline equivalent. Electricity is stored in a 40 kW SAFT Li-Ion battery pack. Top speed is a respectable 80 mph with a zero to 60 mph acceleration time of 16 seconds.

DaimlerChrysler said it would provide a demonstration vehicle to the California Fuel Cell Partnership for evaluation purposes this year. It should be noted that this is just one of many fuel cell concepts Daimler- Chrysler is developing. For instance, the Chrysler Group has a couple of other fuel cell concept vehicles, the Jeep Commander, with an onboard reformer to produce hydrogen from gasoline and the Jeep Commander 2, using methanol as the reforming fuel.