(630c) Method to Release Hydrogen From Ammonia Borane for Portable Fuel Cell Applications

Portable electronic devices are becoming more widespread and power-demanding. Unfortunately, battery improvements are not advancing rapidly enough to meet the need for increased power. Hydrogen powered fuel cell systems have a potential to significantly improve the performance characteristics of portable electronic devices, including duration of their operation, without recharging/replacing the power source. A more widespread use of hydrogen fuel cells, however, is limited by the lack of availability of a practical, high density fuel source. In this context, chemical hydrides, such as ammonia borane (AB, NH₃BH₃), is considered to be a promising hydrogen storage material as it contains 19.6 wt% hydrogen. It is difficult, however, to release hydrogen from AB. Thermolysis, catalytic hydrolysis and heat generated by additional reactive mixtures are usually employed but these methods have disadvantages that decrease the efficiency of hydrogen storage systems. In this paper, we use a new approach to release hydrogen, which does not require any catalyst and produces relatively high hydrogen yield and environmentally benign byproducts. It involves metal/water combustion reactions, which provide heat for AB dehydrogenation and release additional hydrogen from water [1]. One possible design is to mix AB with metal powder and water. However, it is necessary to create conditions for AB thermolysis and prevent its hydrolysis as it provides a lower hydrogen yield (9.1 wt% based on reacted water) than thermolysis (up to 19.6 wt%). Thus, the best design option is to spatially separate AB and metal/water mixture. This approach currently provides H₂ yield up to 9.7 wt%. Our results show that this method is promising for hydrogen storage and could be used in compact power sources for portable electronic devices.