Achieving a novel solvent-free regeneration of LiBH4 combining hydrogen storage and production in a closed material cycle

Abstract

LiBH 4 has been considered as one of the most promising energy storage materials with its ultrahigh hydrogen capacity, which can supply hydrogen through hydrolysis process or realize hydrogen-to-electricity conversion via anodic oxidation reaction of direct borohydride fuel cells (DBFCs). However, the realization of practical hydrogen applications heavily depends on the effective synthesis of high-purity LiBH 4 and recycling of the spent fuels (LiBO 2 ·xH 2 O). The present work demonstrates a convenient and high-efficiency solvent-free strategy for regenerating LiBH 4 with a maximum yield close to 80%, by retrieving its by-products with MgH 2 as a reducing agent under ambient conditions. Besides, the hydrogen released from the regeneration course can completely compensate the demand for consumed MgH 2 . The isotopic tracer method reveals that the hydrogen stored in LiBH 4 comes from both MgH 2 and coordinated water bound to LiBO 2 . Here, the expensive MgH 2 can be substituted with the readily available and cost-effective MgH 2 −Mg mixtures to simplify the regeneration route. Notably, LiBH 4 catalyzed by CoCl 2 can stably supply hydrogen to proton exchange membrane fuel cell (PEMFC), thus powering a portable prototype vehicle. By combining hydrogen storage, production and utilization in a closed cycle, this work offers new insights into deploying boron-based hydrides for energy applications.