Off-board regeneration of ammonia borane for use as a hydrogen carrier for automotive fuel cells T.Q. Hua*, R.K. Ahluwalia Argonne National Laboratory, Argonne, IL 60439, United States article info Article history: Received 4 April 2012 Received in revised form 13 June 2012 Accepted 4 July 2012 Available online 1 August 2012 Keywords: Ammonia borane On-board hydrogen storage Off-board regeneration Hydrazine WTT efficiency GHG emissions abstract Ammonia borane (AB) is a promising chemical hydrogen storage material because of its high H 2 intrinsic material capacity and the exothermicity of the dehydrogenation reac- tions. A major technical barrier for AB, however, is in the development of an energy- efficient regeneration scheme. This paper examines three promising regeneration schemes that are in various stages of development and verification in the laboratory. The first scheme utilizes a thiol to digest the spent fuel and requires reforming formic acid to close the fuel cycle. The second scheme utilizes an alcohol to digest the spent fuel, but not all steps in the process have been formulated or tested. The third scheme is a single-reactor process that uses hydrazine to regenerate spent AB, but the production of hydrazine from hydrogen is itself not a trivial process. Engineering flowsheets were constructed for each of the three regeneration schemes and the process energy requirements for each scheme were calculated. Additionally, total energy requirements across the entire chain of production, delivery, storage, recovery, and regeneration were evaluated to determine the total cycle well-to-tank energy efficiency and greenhouse gas emissions. The well-to-tank efficiency ranges from a low of 8% in one version of the third regeneration scheme to as high as 37% in the second scheme if the missing process steps were to have no impact on efficiency. The estimated greenhouse gas emissions are between 20 and 100 kg CO 2 - equivalent per kg H 2 delivered to the vehicle. Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Ammonia borane (AB), BH 3 NH 3 , is a promising chemical hydrogen storage material for use with automotive fuel cell systems because of its high H 2 intrinsic material capacity and because the dehydrogenation reaction is exothermic. Ammonia borane is a stable solid at room temperature and melts at a temperature between 110 and 114  C [1,2]. Storing H 2 on-board in the form of solid AB poses many practical prob- lems that are generic to any solid fuel that may be considered for transportation and that needs to be regenerated in a central plant off-board the vehicle. These include trans- portation of the fuel from a central plant to the refueling stations, loading of the solid fuel into the vehicle’s fuel tank and unloading of the spent fuel, refueling of fuel tanks that are partially empty, achieving high packing densities, controlling H 2 release and peak temperatures, and conveying the solids to the hydrogen generation reactor. Storing H 2 in the form of a liquid AB overcomes many of these difficulties and presents some advantages of a familiar liquid fuel infrastructure. * Corresponding author. Argonne National Laboratory, 9700 S Cass Avenue, Argonne, IL 60439, United States. Tel.: þ1 630 252 7753; fax: þ1 630 252 3296. E-mail address: hua@anl.gov (T.Q. Hua). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 14382 e14392 0360-3199/$ e see front matter Copyright ª 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.ijhydene.2012.07.013