N101-081 TITLE: Novel Volumetric and Gravimetric Oxygen Sources and Packaging Suitable for Unmanned Applications

TECHNOLOGY AREAS: Ground/Sea Vehicles, Weapons

ACQUISITION PROGRAM: PMS 403, PMS 399, PMS 394, PMS 404

OBJECTIVE: Investigate and demonstrate novel volumetric and gravimetric oxygen sources for
underwater applications with specific energies of 500-700 Whrs/kg at the system level.

DESCRIPTION: Underwater vehicles and weapons must operate in air-independent environments. There is the need to investigate novel oxidizer sources for the operation in the absence of air, and at the same time meet safety, cost and underwater operation requirements.

Underwater vehicles will serve as key elements in integrated operations of future surface ships and submarines, providing a range of support functions including autonomous surveillance, mine counter measures, and special forces transport. However, current power sources for these vehicles (rechargeable silver-zinc or lithium ion batteries or high-energy primary batteries) do not meet the energy requirements for future missions, or they impose a tremendous logistics burden on the host vessel. Fuel cells offer a viable option for meeting mission energy requirements, and at the same time, they can reduce the host vessel logistics burden if the fuel and oxidizer can be stored in a safe, high energy density format.

Fuel cells operating on hydrogen or more complex fuels (such as high energy density hydrocarbons) and oxygen are attractive as underwater power sources because they are efficient, quiet, compact, and easy to maintain. The total energy delivered by a fuel cell system is limited only by the amount of fuel and oxygen available to the fuel cell energy conversion stack. Unlike ground and air transportation fuel cell systems that only require an onboard fuel, underwater vehicles must carry both the fuel and the oxygen source because the oxygen concentration in the ocean is insufficient to meet vehicle power requirements. The underwater vehicle oxygen source must possess a high oxygen content (both weight and volume based) to accommodate the weight and volume constraints of the vehicle design, provide oxygen in a throttleable manner to load follow the fuel cell, and be amenable to safe handling and storage onboard submarines and surface ships.

Gaseous oxygen storage does not provide adequate storage densities, while liquid oxygen storage introduces challenges with handling and storage. Other liquid sources, such as hydrogen peroxide (H2O2) require compact, efficient, controllable conversion methods to produce oxygen and handle reaction byproducts. Solid-state oxygen sources such as sodium chlorate (NaClO3) and lithium perchlorate (LiClO4) possess high oxygen contents and are stable under ambient conditions; however, decomposition of these materials to gaseous oxygen typically employs thermal methods that are often difficult to start, stop, and control.

Therefore, innovative approaches to oxygen storage and generation are sought to address air-independent propulsion needs. The oxygen storage material may be a liquid or solid and may be fed to the conversion system as a liquid, a solid, or a solid in a carrier fluid (preferably water) as a slurry or a solution. The ability to mechanically recharge or replenish the oxygen source should be considered. To meet nominal undersea vehicle power requirements, throttleable oxygen delivery rates should be sufficient to power a typical fuel cell stack from 50 W to 5 kW. Oxygen storage capacity should be scalable to provide a minimum of 50 kilograms of useable oxygen gas. The available oxygen capacity should be maximized on a total system weight basis (i.e. weight percent oxygen), while maintaining a high volumetric density for the overall system.

PHASE I: During Phase I: Demonstrate the volumetric and gravimetric oxygen source analyses to
meet the specific energies of 500-700 Whrs/kg at the vehicle power system level. Conduct laboratory scale testing (TRL 2-3) to demonstrate feasibility of the system concept with high efficiencies (>80%) and evaluate the safety and handling criteria for such oxidizers. Develop a vehicle-level oxygen source system schematic.

PHASE II: Based on Phase I assessments, further develop and optimize prototype demonstrations (TRL 4-5) and scalability approaches for the described system, and demonstrate a degree of commercial viability. Complete safety analyses.

PHASE III: Phase III will be awarded after Phase II prototype demonstration and safety analyses are complete. The system will be ready for in-water demonstration in actual hardware and demonstrate a TRL 6. This demonstration must be completed with a commercial partner and with a commitment from a transition sponsor.

PRIVATE SECTOR COMMERCIAL POTENTIAL/DUAL-USE APPLICATIONS: Technology can benefit
ocean surveillance, underwater mapping industry.

REFERENCES:
1. UUV Master Plan (http://www.navy.mil/navydata/technology/uuvmp.pdf)

2. Fuel Cell Systems, Leo J. M. J. Blomen, Michael N. Mugrewa, Ed., Plenum Publication Corp., NY (1994).

3. Undersea Vehicles and National Needs, National Research Council, National Academy Press, Washington D.C. (1996).

4. An Assessment of Undersea Weapons Science and Technology, National Research Council, National Academy Press, Washington D.C. (2000).

5. Russel R. Bessette, et al., J. Power Sources, 80 (1999) 248-253.

6. Øistein Hasvold, et al., J. Power Sources, 80 (1999) 254-260.

KEYWORDS: air-independent energy sources; liquid oxidants, volumentric/gravimetric oxidizers; replenishability; underwater applications

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