Capacity enhancement of aqueous borohydride fuels for hydrogen storage in liquids

Journal Article · Thu Oct 01 00:00:00 EDT 2015 · Journal of Alloys and Compounds

DOI:https://doi.org/10.1016/j.jallcom.2015.01.063· OSTI ID:1225147

Schubert, David ^[1]; Neiner, Doinita ^[1]; Bowden, Mark ^[2]; Whittemore, Sean ^[2]; Holladay, Jamie ^[2]; Huang, Zhenguo ^[3]; Autrey, Tom ^[2]

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1. U.S. Borax Inc., Rio Tinto, CO (United States)
2. Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
3. Univ. of Wollongong, NSW (Australia)

In this work we demonstrate enhanced hydrogen storage capacities through increased solubility of sodium borate product species in aqueous media achieved by adjusting the sodium (NaOH) to boron (B(OH)₃) ratio, i.e., M/B, to obtain a distribution of polyborate anions. For a 1:1 mole ratio of NaOH to B(OH)₃, M/B = 1, the ratio of the hydrolysis product formed from NaBH₄ hydrolysis, the sole borate species formed and observed by 11B NMR is sodium metaborate, NaB(OH)₄. When the ratio is 1:3 NaOH to B(OH)₃, M/B = 0.33, a mixture of borate anions is formed and observed as a broad peak in the 11B NMR spectrum. The complex polyborate mixture yields a metastable solution that is difficult to crystallize. Given the enhanced solubility of the polyborate mixture formed when M/B = 0.33 it should follow that the hydrolysis of sodium octahydrotriborate, NaB₃H₈, can provide a greater storage capacity of hydrogen for fuel cell applications compared to sodium borohydride while maintaining a single phase. Accordingly, the hydrolysis of a 23 wt% NaB₃H₈ solution in water yields a solution having the same complex polyborate mixture as formed by mixing a 1:3 molar ratio of NaOH and B(OH)₃ and releases >8 eq of H₂. By optimizing the M/B ratio a complex mixture of soluble products, including B₃O₃(OH)₅^2-, B₄O₅(OH)₄^2-, B₃O₃(OH)^4-, B₅O₆(OH)^4- and B(OH)₃, can be maintained as a single liquid phase throughout the hydrogen release process. Consequently, hydrolysis of NaB₃H₈ can provide a 40% increase in H₂ storage density compared to the hydrolysis of NaBH₄ given the decreased solubility of sodium metaborate. The authors would like to thank Jim Sisco and Paul Osenar of Protonex Inc. for useful discussion regarding liquid hydrogen storage materials for portable power applications and the U.S. DoE Office of Energy Efficiency and Renewable Energy Fuel Cell Technologies Office for their continued interest in liquid hydrogen storage carriers. Pacific Northwest National Laboratory is a multi-program national laboratory operated for DOE by Battelle. The authors dedicate the work to the memory of Professor Sheldon Shore. His contributions to boron hydride chemistry set the foundation for many who have followed.

• Research Organization: Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
• Sponsoring Organization: USDOE
• DOE Contract Number: AC05-76RL01830
• OSTI ID: 1225147
• Report Number(s): PNNL-SA-105083; HT0202000
• Journal Information: Journal of Alloys and Compounds, Vol. 645, Issue S1; ISSN 0925-8388
• Publisher: Elsevier
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
liquid hydrogen storage
solubility
polyborate mixtures.