Single LiBH4 nanocrystal stochastic impacts at a micro water|ionic liquid interface

Abstract LiBH 4 is often employed as a reducing agent for metal nanoparticle (NP) preparation but is inherently a solid-state H 2 hydrogen storage agent. Herein it is shown, through a combination of electron/optical microscopies and single entity electrochemical study, that LiBH 4 is stored in the solid state within an ionic liquid (IL) as nanocrystals (NCs). The electrochemical monitoring of an immiscible water|IL (w|IL) micro-liquid|liquid interface (LLI) shows interfacial charge exchange associated with the stochastic impacts of single NCs. Meanwhile, in situ optical monitoring of a w|metal or w|IL interface shows that such impacts are associated with the development of a H 2 -in-IL micro/nano-foam related to the poor solubility of H 2 . Both the presence of solid NCs and the latter H 2 -in-IL foam suggest that H 2 release from LiBH 4 -in-IL is a slow, but likely controlled process. The rate of H 2 production at a macroscopic LLI is further confirmed by gas chromatographic measurements, in very good agreement with microscopic observations. The electrochemical LLI provides unique investigative access to LiBH 4 NCs and offers insight into H 2 storage in ILs, or for direct borohydride fuel cells, as well as NP synthesis.