Fuel Cell Progress Reported at the 41st Power Sources Conference

U.S. Army Searches for Rugged Fuel Cells for Trench Warfare

A fuel cell power source can meet the new battleground requirement of not emitting heat and electromagnetic radiation that an enemy can use to detect its location. However, the fuel cell must also perform in the extreme hot and cold temperatures that exceed the requirements of fuel cells that are met by fuel cells designed for other present-day applications. Durability and reliability are strict requirements, and in this service the fuel cell will almost never be operating on a flat surface and be perfectly upright.

Elizabeth Bostic described a unique program, developed by the U.S. Army Communications Electronics RD&E Center (CERDC), for acquiring a fuel cell that meets the requirements of reliable operation in a battlefield environment (5). Requirements were identified for these three fuel applications:

    Soldier and sensor power (under 100 watts)

    Stand-alone battery charging (100 to 500 watts)

    Auxiliary power units (500 watts to 10kW)

The CERDC then developed the requirements for these applications and invited foreign vendors to supply “near production” systems that could be evaluated for rapid transition into units that would meet field requirements. The goal in testing the low-power systems was to compare the power quality, energy density, and overall performance to that of standard military batteries. Performance of the higher power systems was compared against data for the tactically quiet generator sets in the field today. The units that were subsequently adopted for testing are listed in Figure 2.

Bostic described the results of testing two SFC A25 units that had been leased from Smart Fuel Cell (SFC) AG which is based in Brunnthal-Nord, Germany. The system weighed 22 pounds and was 18.25” by 6.5” by 12.25” in size. A unit was run for a full 8-hour day at ambient temperature (20°C to 25°C) on three different occasions. The fuel consumptions and efficiencies, based on the lower heating value of methanol, are in Figure 3.

At higher temperatures the unit began producing shutdowns at 35°C. At 45°C the system would not carry a load. The system did not start or operate at +15°C. The tests did show the load durations at which the A25 fuel-cell system would weigh less than batteries (Figure 4).

Bostic concluded that current fuel cell technology has not advanced to the point where effective and reliable operation in military environments and conditions is feasible. In order for fuel cell technology to make real strides in commercialization and substantial use in the military, the focus must be placed on developing ruggedized complete systems that operate consistently and reliably on the battlefield.

PEM Fuel Cells for U.S. Army’s
“Silent Watch” Combat Vehicles

On March 1, the U.S. Army created a new organization that intends to become the world leader in military research, development, and engineering. It is the U.S. Army Research, Development and Engineering Command (RDECOM), headquartered at Aberdeen Proving Ground, Maryland. The command seeks out and develops the latest technology to provide the most advanced weapons, communications, clothing, food, and vehicles.

An increasingly important combat vehicle application is a tactical mode of operation that requires meeting stringent acoustic and infrared levels. Enemy forces can often hear vehicle engines and portable power generators well before establishing visual contact. They can then strike the army’s assets without warning. Therefore, “Silent Watch” configurations currently use the vehicle’s batteries to power large communications and situation-awareness electronic equipment in the vehicle cabin. However, these batteries cannot be used for extended periods of time, like over one hour. Fuel cells, with low operational signatures and improved efficiency, may provide the army a solution for Silent Watch applications. Therefore RDECOM joined IdaTech to fabricate and integrate a 2kW liquid-fuel cell auxiliary power unit on a C3OTM-vehicle test bed to enhance its Silent Watch capabilities. IdaTech had previously developed fuel cell modules that ranged from 1 to 50kW. Rene Dubois from IdaTech described the results from a six-month timeline for building the fuel cell and integrating it on the vehicle (6).

The 2kW fuel cell system had to operate on approved fuels and could not weigh over 260 pounds. IdaTech chose its 1kW FCS-1200 methanol system as a backbone for the C3OTM 2kW APU. With modifications of the fuel reformer and balance-of-plant sections, the Mobile Power Plant (MPP) unit was ready for test in four months. The MPP consists of two 1kW fuel cells, developed by Ballard Inc., and an IdaTech methanol steam reformer.

The methanol-water fuel is pumped into the fuel reformer where the fuel is vaporized and sent through a catalytic reforming bed. There the vapors react over the catalyst to form hydrogen and carbon dioxide gas, plus small amounts of trace molecules such as carbon monoxide. The gases go to a selective membrane that lets the small hydrogen molecule penetrate, and rejects the larger carbon-based molecules and other residual trace elements. The exhaust stream goes to a burner that heats the reformer and vaporizes the incoming fuel. The hydrogen goes to the PEM stacks that produce the output power. The balance-of-plant includes power electronics, sensors, electronics, control boards, and heaters for freeze prevention in cold weather.

The MPP was connected to a 24-volt DC bus inside the vehicle’s cabin. Also connected to the bus was a 24-volt lead-acid battery. During normal Silent Watch operation the battery supplied power to the communication and electronic equipment on the vehicle, and the MPP kept the battery charged.

Acoustics-test results for the Silent Watch vehicle with its engine running, and with engine not running, are summarized in Figure 5. At 50 feet from the vehicle the fuel cell system’s acoustic signature could not be discerned from ambient noise. Follow-on testing will subject the vehicle to various environments, including dust, wind, rain, snow, excessive vibration and shock, sub-freezing temperatures, and low humidity.

One of the remaining challenges is the need to operate on military fuel. Under the military’s one-fuel policy, all fueled military systems must operate on logistic fuels such as JP-I and diesel fuel.

U.S. Navy 625kW Ship Service Fuel Cell
Generator and Power for Underwater Vehicles

The U.S. Navy had recognized by 1997 the potential benefits of fuel cell power on shipboard. It then started with the development of a conceptual 2.5MW power plant which could operate with naval logistics fuel that contained up to 1% sulfur by weight. Preliminary design and systems analyses included determining the optimum fuel cell stack, its support system, plus power conditioning alternatives for meeting shipboard voltage requirements. Denise Chen described the results of this work and the selection for development of a 500kW integrated logistics-fuel processor and a 625kW molten-carbonate fuel cell generator for construction and test (7). Anthony Nickens described plans for demonstrating the performance of the 625kW molten-carbonate fuel cell generator (8). After the completion of testing in 2005, the module may be installed aboard a ship for an at-sea demonstration.

The 625kW molten carbonate fuel cell generator includes dual regenerable hydrogen-sulfide sorbent reactors, and a pre-former that generates sulfur free, methane-rich, reformate, plus two molten carbonate fuel cell stacks (Figure 6). The reformate gas stream is suitable for internal reforming in the commercial-product based fuel cells. This system will be land-base tested at the Naval Surface Warfare Center, Philadelphia, in 2005.

The parallel program for designing and testing a 500kW integrated fuel processor and a proton exchange membrane for fuel cell application is proceeding under the supervision of SOFCO Electrochemical Fuel Systems, with engineering and test facilities provided by the Idaho National Engineering and Environmental Laboratory. The fuel processor includes an autothermal reformer, dual regenerable desulfurizers, and carbon monoxide reduction reactors. The process is completely integrated and includes dual turbo compressors, a steam generator, heat recovery, and fully automatic controls.

Propelling U.S. Navy’s Underwater Vehicles with Semi Fuel Cell Power

An unmanned underwater vehicle after launch has no connection to a supporting power source. It must therefore carry a power source that delivers required power during its specified mission duration. Battery power sources have been used in the past, but a battery requires frequent checking and testing to assure that it can deliver the mission’s required energy. Electrochemical energy is preferred over internal combustion engines because it is quiet, and battery and fuel cell power sources can be recharged with minimum expense and downtime.

Charles J. Patrissi described the U.S. Navy investigations of alternatives for supplying propulsion power for underwater vehicles (9). He observed that energy density is a critical enabler for autonomous systems such as unmanned underwater vehicles (UUV). With no energy lifeline, UUV mission time depends on the energy stored on board the vehicle. Electrochemical energy is favored over internal-combustion power because it is quiet, and with batteries and fuel cells the power source can be recharged with minimum expense and downtime. Safety is a significant issue. As more energetic electrochemical couples are being explored and developed, special procedures are being written to ensure that they are safe to carry on U.S. Navy vessels.

Lithium-seawater batteries have demonstrated high current density, even above the 300mA/cm2 needed in high-power torpedoes. Challenges emanated from the high reactivity of lithium with water and the resulting hydrogen evolution. The Naval Undersea Warfare Center (NUWC) is presently developing Mg-H2O2-SFC (semi-fuel-cells) which have a high potential for energy density on a systems basis, low per-run cost, and safe operation. Recently Mg is being replaced in an effort to obtain a higher SFC voltage and specific energy.

High cell voltage (3V) and specific energies of 668 to 725Wh/kg have been measured in experiments. Lithium efficiency is limited to approximately 55% by corrosion in the aqueous hydroxide electrolyte. The resulting hydrogen gas is a concern for maintaining the stealth of underwater vehicles. One alternative may be to use the hydrogen to power a PEM fuel cell with oxygen provided from the H2O2 being used for the SFC. Corrosion inhibitors will be investigated for increasing Li efficiency and SFC energy density. Polarization experiments show that SFC voltage will decrease rapidly if the critical current density is exceeded. However, power production resumes quickly if current is decreased. Safety with respect to the hydrogen gas will be part of future studies. Other researchers have shown how electrochemical operation could be turned off without continuous evolution of hydrogen by purging the anode compartment with an inert atmosphere or liquid. These investigations show that the Li- H2O2 and SFC operating parameters must be optimized and closely controlled to meet UUV energy and power requirements.

Conclusion

Fuel cells, lithium-ion batteries and other batteries were topics of many other papers that were presented at the 41st Power Sources Conference. Rather than summarize all the 27 fuel cell papers, I chose to summarize those that showed clearly that fuel cell performance is improving, its useful lifetime is growing, and many new applications are developing. It is also obvious that intense and well-funded research effort is directed toward making fuel cells a practical and economical power source. Fuel-cell powered and hybrid vehicles can become an efficient substitute for vehicles powered by petroleum-based fuels after the world’s petroleum production begins to diminish in 2005.

More fuel cell data can be found in the “Proceedings of the 41st Power Sources Conference,” available from Palisades Convention Management, 411 Lafayette St., Suite 201, New York, NY 10003.

References

1. Karanjikar, Mukund, and associates, “Logistic Fuel to Hydrogen – Fuel Processing using Microfibrous Entrapped Catalysts and Sorbents for PEM Fuel Cell,” pages 231 to 234.

2. Oman, H., “Cells That Make Power from Fuels,”Energy Systems Engineering Handbook,” Prentice Hall Inc., 1986, page 227.

3. 2001-2002 GTW Handbook, “Industry Price Levels, Combined Cycle Power Plants,” page 37.

4. Shah, Shailesh and associates, “Advancements in Hydrogen on Demand TM Fuel Systems for Military and Consumer Electronic Devices,” pages 247 to 251”.

5. Bostic, Elizabeth and associates, “The U.S. Army Foreign Comparative Test Fuel Cell Program,” pages 267 to 370.

6. Dubois, Rene, and Sifer, Nicholas Xavier, “Multi-Fuel Type PEM Fuel Cell Systems for Military APU Applications,” pages 371 to 374.

7. Chen, Denise, and associates, “Integrated Logistic Fuel Processor for PEM Fuel Cell Application,” pages 235 to 238.

8. Nickens, Anthony, and associates, “Molten Carbonate Fuel Cell Generator for Ship Service Applications,” pages 363 to 366.

9. Patrissi, Charles J. and associates, “Investigating a Li-H2O2 Semi Fuel Cell with a Microfibrous Cathode as a Power Source for Unmanned Underwater Vehicles,” pages 420 to 423.