In Situ Formation of TiB₂ Nanoparticles for Enhanced Dehydrogenation/Hydrogenation Reaction Kinetics of LiBH₄–MgH₂ as a Reversible Solid-State Hydrogen Storage Composite System

Abstract

To enhance the dehydrogenation/rehydrogenation kinetic behavior of the LiBH 4 −MgH 2 composite system, TiF 4 is used as an additive. The effect of this additive on the hydride composite system has been studied by means of laboratory and advanced synchrotron techniques. Investigations on the synthesis and mechanism upon hydrogen interaction show that the addition of TiF 4 to the LiBH 4 −MgH 2 composite system during the milling procedure leads to the in situ formation of well-distributed nanosized TiB 2 particles. These TiB 2 nanoparticles act as nucleation agents for the formation of MgB 2 upon dehydrogenation process of the hydride composite system. The effect of TiB 2 nanoparticles is maintained upon cycling.

Tuning LiBH4 for Hydrogen Storage: Destabilization, Additive, and Nanoconfinement Approaches

“…As seen in Figure 6, Ti containing additives added to 2LiH + MgB 2 show excellent performance with capacities over 8 wt %, and times are ranging between 30 min to 50 min. These results evidence an enormous reduction from the 10 to 15 h required for the first decomposition of the pristine 2LiBH 4 :MgH 2 , though the temperature condition is still quite high for an application [36,38,39,46,49,[58][59][60][61][62][63][64][65][66][67].…”

“…The reversibility of pristine LiBH 4 demands harsh conditions (>600 • C and >100 bar H 2 ) [1,41], which makes it impossible for its direct use as a hydrogen storage medium for practical applications. Several investigations have been done heading towards thermodynamic destabilization and kinetic improvement of LiBH 4 [29,30,39,46,49,50,53,[58][59][60][61][62][63][64][65][66][67]69,[72][73][74][75][76][77][78][79][80][81][82][83][84][85][86][87][89][90][91][92][93][94][95][96][97][98][99].…”

“…Based on this analysis, it is clear that the mutual destabilization effect between LiBH 4 and MgH 2 only occurs upon hydrogenation, but at relatively low temperatures (<413 • C) under equilibrium conditions. For the hydrogenation process carried out under dynamic conditions, the applied temperatures were usually in the range between 300 • C and 400 • C [33][34][35][36][37][38][56][57][58][59][60][61][62][63][64][65][66][67]; hence, the mutual destabilization effect was verified by a one-step curve of hydrogen uptake against time. However, for the dehydrogenation, the thermodynamics limits the behavior of Li-RHC to two main reaction steps, losing the benefit of the destabilization effect.…”

“…The most applied approach to improve the kinetic behavior of the 2LiBH 4 + MgH 2 system was the addition of transition metal (TM) and transition metal compounds (TMC) via mechanical milling [68]. Several works were published about the improvement of the kinetic behavior, and also cycling stability of TM-and TMC-added Li-RHC [56][57][58][59][60][61][62][63][64][65][66][67]. In 2010, Bösenberg et al [57] studied the effects of TMC on the kinetic behavior of Li-RHC and proposed global reaction rate mechanisms for the absorption and mainly desorption of hydrogen.…”

“…Therefore, it was proposed that nanostructured TMB species can act as heterogeneous nucleation sites for MgB 2 , thus improving the dehydrogenation rate of the slowest step, i.e., the decomposition of LiBH 4 (second step), since the decomposition of MgH 2 is quite fast. Based on this concept, either TMBs were added to Li-RHC or TM, and TMC were used as sources to form in situ TMB through the interaction with the Li-RHC [40,[56][57][58][59][60][61][62][63][64][65][66][67]. Puszkiel et al [39,69] proposed another mechanism to explain the effect of a specific TMC on the kinetic behavior of Li-RHC.…”