Efficient hydrogen release from LiBH4 alcoholysis in methanol/ethylene glycol based solutions over a wide temperature range

Abstract

Hydrolysis of LiBH4 (LB in short) is considered as a potential means of releasing the hydrogen stored in the hydride and the water. However, the hydrolysis of LB occurs only above 0 °C and efficient catalysts are required to accelerate the hydrogen kinetics. Here, we demonstrate an efficient non-catalytical hydrogen generation system that enables H2 production of LB over a wide range of temperatures with methanol (referred to MeOH), ethylene glycol, and MeOH/water mixtures as reaction solvents. The results indicate that the hydrogen kinetics of LB is controllable by MeOH dose, MeOH species, reaction temperature, and solution components. For instance, the hydrogen evolution rate could be accelerated from 266 to 515 mLH2 min−1 g−1 (per unit weight of LB) with a H2 yield up to 93% by tailoring the dose of methanol at 25 °C. Notably, the glycolysis kinetics is much faster than that for the methanolysis of LB, delivering a hydrogen rate varying from 523 to 10,125 mLH2 min−1 g−1. By optimizing reaction conditions, a gravimetric hydrogen density of ~4.6 wt% H2 was realized in the LB-MeOH system. Interestingly, the methanolysis/glycolysis products of LB can spontaneously convert into MeOH and hydrated byproduct (LiBO2‧2H2O) by reacting with water, and MeOH may be separated and reused as an intermediate. Here, LiBO2‧2H2O can be easily regenerated back to LB by ball milling with Mg under ambient conditions. Thus, a hydrogen cycle combining hydrogen generation and storage in a closed material cycle is achieved, which may lay the foundation for developing practical hydrogen sources for mobile/portable applications.