LiBH4 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 LiBH4 is stored in the solid state within an ionic liquid (IL) as nanocrystals (NCs). The electrochemical monitoring of an immiscible water vertical bar IL (w vertical bar IL) micro-liquid vertical bar liquid interface (LLI) shows interfacial charge exchange associated with the stochastic impacts of single NCs. Meanwhile, in situ optical monitoring of a w vertical bar metal or w vertical bar 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 LiBH4-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 LiBH4 NCs and offers insight into H-2 storage in ILs, or for direct borohydride fuel cells, as well as NP synthesis. (C) 2018 Elsevier Ltd. All rights reserved.