Ammonia borane, H3NBH3, has been pegged as an ideal fuel cell material due to its very high hydrogen density (19.6 %). However, so far it has failed to perform as well as expected, as the release of hydrogen leads to the formation of borazine, which is resistant to further hydrogen release and can deactivate the catalyst used in this reaction. Therefore, very few systems have been developed which produce more than 2 equivalents of hydrogen from ammonia borane.
A team of scientists from the University of South Carolina may have solved this problem, using a novel ruthenium catalyst which not only catalyses the release of 2.7 equivalents of hydrogen, but which can dehydrogenate the borazine formed, eliminating it from the system. This has not been achieved for any of the high-performing catalysts reported to date. This catalyst is able to polymerise the borazine to polyborazylene, liberating hydrogen in the process.
This result is big news for the hydrogen fuel cell area, especially as this catalyst is air and moisture tolerant, is reusable and requires low catalytic loadings. The utilisation of ammonia borane as a hydrogen fuel source may finally become a reality through technologies like this.
This work was published in Dalton Transactions in March 2016, and can be found online here.