Superior Catalytic Effects of Transition Metal Boride Nanoparticles on the Reversible Hydrogen Storage Properties of Li‐Mg‐B‐H System

Abstract

Onboard hydrogen storage has been recognized as one of several scientifi c challenges in promoting hydrogen fuel cell-powered vehicles. [ 1,2 ] As potential hydrogen storage material, lithium borohydride, LiBH 4 , has received a signifi cant attention during the past few years because of its extremely high gravimetric (18.5 wt%) and volumetric (121 kg m − 3 ) hydrogen content. [3][4][5][6][7] However, the use of LiBH 4 as an on-board hydrogen storage material is hindered due to both thermodynamic and kinetic defi ciencies. Several strategies, like nanoconfi nement, [8][9][10][11][12][13] catalyst doping, [14][15][16][17][18] and reactant destabilization [19][20][21][22][23][24][25] have been used to modify the hydrogen storage properties of LiBH 4 . All of these technological advances have enabled considerable improvements in reversible hydrogen storage properties of LiBH 4 . Particularly, the employment of reactant destabilization strategy to form reactive hydride composites (RHCs) has been proven to be effective to stabilize the dehydrogenated state and then lower the total reaction enthalpy. LiBH 4 /MgH 2 systems in a 2:1 molar ratio constitutes a representative RHC, which reduces the reaction enthalpy by 25 kJ mol −1 H 2 in comparison with the pristine LiBH 4 by forming MgB 2 : [ 19 ] When being operated under a back hydrogen pressure of 3-5 bar, the 2LiBH 4 -MgH 2 composite undergoes the above reaction, giving a theoretical hydrogen capacity of 11.5 wt%, largely surpassed the ultimate hydrogen storage target of 7.5 wt% proposed by United State Department of Energy (DOE). [ 26 ] However, the real kinetics of the undoped Li-Mg-B-H system is sluggish and high temperature is needed to give an acceptable dehydrogenation rate. Thereby, great efforts have been devoted to exploring effi cient additives, which can be classifi ed as chlorides, [27][28][29][30] fl uorides, [30][31][32][33][34][35] and oxides. [35][36][37] Undoubtedly, these additives improved the kinetics of RHC systems. Yet, almost all of these dopants will generate some by-products, which will take up some weight in the system, causing a decrease of reversible hydrogen storage capacity. [27][28][29][30][31][32][33][34][35][36][37] Besides, to get an improved kinetics, activation process is needed. [ 29,33,35 ] Moreover, the kinetics and cycling stability should be further improved for its practical application. Therefore, the development of highly efficient and highly dispersed catalyst is urgently important.Here, we devote the work to nanoparticles of transition metal borides (NbB 2 , ZrB 2, and CeB 6 ) synthesized by wet chemistry method and report the fi rst systematic study of Li-Mg-B-H systems catalyzed by the transition metal boride nanoparticles. Superior catalytic effect with favorable cycling stability is achieved for the nanoboride-enhanced systems without generating by-products, which, in turn, leads to a higher usable gravimetric capacity and goes beyond the early work concentrated on the dopants of halides or oxides. A detailed mechanis...

Superior Kinetic and Cyclic Performance of a 2D Titanium Carbide Incorporated 2LiH + MgB2 Composite toward Highly Reversible Hydrogen Storage

“…Nanoconfinement , and incorporation of catalysts − are effective approaches to improve the kinetic performance of the 2LiBH 4 + MgH 2 /2LiH + MgB 2 system. Nevertheless, nanoconfinement has the shortcomings of low loading of hydrogen storage material, high cost of framework, and complex fabrication process.…”

“…Incorporation of catalytic additives can reduce both dehydrogenation and hydrogenation kinetic barriers. Metal oxides, − halides, − and borides − have been investigated as additives to this system. Among them, a series of Ti-based additives, such as TiCl 3 , , TiO 2 , 3TiCl 3 ·AlCl 3 , TiF 3 , TiF 4 , TiN/TiC/Ti/TiH 2 , TiB 2 , , and Ti isopropoxide, are beneficial but with different efficiency.…”

Achieving High Dehydrogenation Kinetics and Reversibility of LiBH4 by Adding Nanoporous h-BN to Destabilize LiH

“…For example, it is effective to destabilize LiBH 4 by forming a LiBH 4 –MgH 2 composite, but the formed compound MgB 2 limits the dehydrogenation kinetics . As another example, additives such as oxides or halides can catalyze the dehydrogenation of LiBH 4 , but they react with LiBH 4 at high temperatures, and thus, reduce the reversible hydrogen storage capacity of the system severely. , Some additives, such as borides − and carbon-based materials, − have been found to function as catalysts without side reactions. For example, nanostructured CoB could facilitate the main dehydrogenation of LiBH 4 at around 350 C and retain the hydrogen capacity of LiBH 4 at ∼9.6 wt % after four cycles .…”

In search of the elusive IrB2: Can mechanochemistry help?

“…Titanium diboride (TiB 2 ) ceramics have a very high Young's modulus (~565 GPa) [1], zirconium and hafnium diboride (ZrB 2 and HfB 2 , respectively) composites exhibit high oxidation resistance [2][3][4][5][6], magnesium diboride (MgB 2 ) is a superconducting phase with a T c among the highest of the conventional superconductors [7] and niobium diboride (NbB 2 ) nanoparticles have applications in catalysis as well as reversible hydrogen storage [8]. While many of the diborides find practical uses as abrasion and oxidation resistant coatings, there are ongoing searches for new phases and compositions that will possess interesting and useful properties.…”