(127b) Mobile Hydrogen Storage in CO2 Treated Ammonia Borane Complexes and Its Design Implications

Ammonium borane (AB, NH₃BH₃) is a promising on-board, solid-state hydrogen storage material (chemical hydride) with a high hydrogen content of 19.6 wt.%. Hydrogen extraction from AB has been carried out via hydrolysis, methanolysis, or pyrolysis (thermolysis or thermal decomposition) but hydrolysis and methanolysis accompany an additional component of H₂O and methanol. Thus, it lowers hydrogen storage capacities for vehicular applications. The thermolysis of AB is mostly employed to extract hydrogen from AB and involves three sequential steps occurring around 110, 150 and 1100 ^oC, with 6.5 wt. % of hydrogen liberated in each step. A primary research challenge for adopting AB as a hydrogen storage material is to enhance dehydrogenation rate at low temperatures around 85 ^oC that is the operating temperature for polymer electrolyte membrane fuel cells and also prevents the generation of byproducts (like borazine, harmful to electrodes). Several approaches have been discussed to thermolytically enhance the dehydrogenation kinetics of AB such as compositing AB with mesoporous materials, dispersing AB in ionic liquids, and adding catalysts and 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 very high. Using transition metals or promoters adds up the cost of hydrogen storage system. As a result, the research efforts have continuously made to find cheap and effective promoters for hydrogen release without negatively impacting the storage capacity. In this talk, I will discuss the promoting effect of CO₂ on the dehydrogenation of solid AB and PAB (polyaminoborane) at 85 ^oC. Beyond the enhanced dehydrogenation kinetics of AB, I will also introduce design implications of hydrogen storage systems using AB complexes and present an economically-viable conversion process of CO₂ to carbon materials using AB.