Direct Ammonia-Borane Alkaline Fuel Cell with In Situ Electrolyte Replacement

As a water soluble powder with 19.6 wt% hydrogen, borazane (ammonia-borane, NH3BH2) is an excellent source of hydrogen for fuel cells. In Phase I of this project we demonstrated that a fuel cell can directly consume NH3BH3 from an aqueous solution and produce 160 mW/cm² with 80% of the fuel utilized electrochemically while operating at current densities suitable for portable devices. Using a high energy density solid fuel as the energy storage medium with a small volume of recirculated water to deliver it to the stack makes it possible to produce a system with a net energy density of over 1 kWh/kg. In Phase II of this project we will build a self-contained 20W (net) power supply that is fed solid NH3BH3. The fully fueled unit will weigh less than 1,400 g and operate for at least 72 hr on a single tank of fuel. It will operate at rated power for at least two weeks with only periodic refueling. At the end of two weeks it will be necessary to replace the electrolyte and the CO2 scrubber. If the scrubber is not replaced, the unit will continue to operate, but performance will gradually decline.