High Pressure High Temperature Polymerization of Ammonia Borane in Porous Silica Matrix

Ammonia borane (AB) is of great interest for chemical hydrogen storage as it has one of the highest releasable hydrogen content of 19.6 wt.% [1,2]. Hydrogen is released in several steps upon heating at relatively low temperature along with the polymerization of ammonia borane to form polyaminoborane, polyiminoborane and, at still increasing temperature, boron nitride [3]. Here we present our high pressure high temperature study on ammonia borane confinement in siliceous zeolite theta-1 (TON) and silicalite-1F (MFI) porous templates. Our recent high pressure high temperature (HPHT) synchrotron x-ray diffraction and Raman spectroscopic experiments revealed that the compression of AB/TON or AB/MFI composite materials promotes the insertion of ammonia borane into the pores of a template. Its further high temperature treatment results in a release of a significant amount of hydrogen and in the formation of polyaminoborane and polyiminoborane polymers, both in the bulk ammonia borane outside the zeolite, as well as confined in the channels of the porous template. In consequence, strong expansion of the zeolite pores accompanied with significant increase of the unit cell volume and series of phase transitions have been observed [4]. Financial support from the Agence Nationale de la Recherche (ANR-19-CE08-0016) is gratefully acknowledged.