(319a) Enhanced Dehydrogenation Kinetics Via Thermal and Carbon Dioxide Treatments
AIChE Annual Meeting
Tuesday, October 18, 2011 - 12:30pm to 1:05pm
Ammonium borane (AB, NH3BH3) is an attractive on-board, solid-state hydrogen storage material, because it has a hydrogen density of 19.6 wt. %. Hydrogen release from AB can be achieved through three approaches, including thermolysis, hydrolysis, and methanolysis. In specific, the thermolysis of solid AB includes three consecutive steps, occurring around 110, 150, and > 500 oC, with about 6.5 wt. % of hydrogen, regarding the mass of AB, desorbing in each step. Slow hydrogen release at temperatures around 85 oC makes pristine AB infeasible as an on-board hydrogen storage medium because most of polymer electrolyte membrane fuel cells operate at this temperature. Several approaches have been discussed to enhance the dehydrogenation kinetics of AB such as compositing AB with mesoporous materials, dispersing AB in ionic liquids, and adding transition metal catalysts or chemical promoters. One major drawback associated with the first two approaches is the low hydrogen storage capacity, as a result of the mass fraction of mesoporous materials and ionic liquids being usually very high. Using transition metals or promoters adds up the cost of H2 storage system. Therfore, the research efforts have continuously made to find cheap and effective promoters for hydrogen release without negatively impacting the storage capacity. This work presents two methods for promoting hydrogen release using thermal treatments of AB at 80 oC and CO2 pretreatments of AB at 60 - 80 oC. These two pretreatments do not require any expensive materials to enhance the kinetics and not reduce the H2 storage density. Within an hour, hydrogen release goes up to 7.1 wt% and 8.33 wt% of AB in the thermal and CO2 pretreatment. We will propose possible mechanisms of the fast H2 release using Raman, IR, and NMR spectroscopic methods.