PNNL

Abstract

Hyperpolarized (HP) 129Xe NMR was used for the first time to probe the porosity for nanophase ammonium borane (AB) infused in mesoporous silica (MCM). Variable temperature HP 129Xe NMR measurements have been systematically carried out on a series of AB:MCM materials with different AB loading. Three distinct types of pore environments are clearly evident: pristine mesopores; pores coated with AB inside the meso-channels, and inter-particle spacing formed from AB aggregates outside the meso-channels. We found similarly uniform coating of AB on mesoporous silica channels with 1:2 and 1:1 AB:MCM loading (ratio of weight percent). When the loading of AB to MCM is larger than 1:1, AB starts to aggregate outside the meso-channels. Further increases in loading (= 3:1) result in the formation of partially blocked meso-channels as a result of excessive AB loading. The detailed information obtained from this study on how supported AB resides in nanoporous channels and how it evolves with the increase of AB loading is helpful for rational design of novel materials with optimal hydrogen storage and release properties.