SBIR-STTR Award

A lightweight hydrogen fuel source is proposed, consisting of a reactor utilizing liquid ammonia (NH3) and solid (powdered) aluminum hydride (AlH3). The package includes a control block and a filter. This package can safely provide hydrogen to a hydrogen/air fuel cell (H/AFC) within the power range of 10-500 W, with sufficient fuel for 1 kWhr of energy. With total weight less than 1 kg and total package volume less than or equal to 1 liter, the unit is suitable for integration with a H/AFC for portable applications. The unit can be produced in sizes tailored to specific power requirements. The reaction of interest is NH3 + AlH3 = AlN + 3H2 + 45 kcal of heat. Stoichiometric reactants for production of 1 kWhr of energy are 170 g of liquid NH3 and 300 g of AlH3. The only gaseous byproduct of the reaction is hydrogen; all other byproducts are solid phase. This Phase I effort includes determination of reaction kinetics, developing controlled operation of hydrogen production, control of reaction heat release, optimization of the reaction to decrease released heat, and development of a near-optimum design for packaging the reactor components.

Benefits:
It is anticipated that the Army will gain from this R&D effort a hydrogen source which is at or near 1 Wh of energy per gram of total source mass, including reactants and packaging. This source should be easily adaptable as a fuel supply for hydrogen/air fuel cells, which can be used as portable power sources for a variety of recreational purposes. Primary recreational applications will be portable GPS systems, emergency beacons, and small portable appliances and equipment which utilizes low-power electronics

A portable hydrogen source for proton exchange membrane fuel cells (PEMFCs) is proposed. The design utilizes both an exothermic reaction between ammonia (NH3) and aluminum hydride (AlH3) and ammonia decomposition. This process is initiated by catalytic decomposition of a small amount of NH3 at about 450 °C temperature and is subsequently self-sustained to provide hydrogen to the fuel cell on demand. Expected hydrogen yield is 1.7 liters per gram of reactants, representing 2.6 Wh per gram of reacting materials, computed by Army guidelines. An integrated hydrogen source package producing 300 Wh to 1000 Wh will have a packaged energy density of between 1.1 Wh and 1.6 Wh per gram of system weight. The hydrogen source will include an ammonia tank, reactor with a heating element and AlH3 block, a control block, and tubing and passive valve arrangement. This package will also include a special filter, which can absorb 20% of its mass in impurities such as NH3, and reduce them to less than 1 ppm. The proposed effort will include a study of reaction kinetics, optimum reactor design for heat utilization, component ratio optimization, a control system for on-demand hydrogen, and a commercial prototype with 1 kWh energy capacity.

Keywords:
Ammonia Fuel Cell Portable Power Hydride Hydrogen