Recent advance of metal borohydrides for hydrogen storage

Mo2N-Activated Metal Borohydride Nanocomposites for H2 Storage

Metal hydrides play a pivotal role in advancing the hydrogen economy by providing a compact solution for onboard hydrogen storage. However, their practical application is hindered by undesirable side reactions and slow kinetics during hydrogen uptake and release. We present herein enhanced thermodynamics and kinetics of hydrogen uptake/release through the infiltration of lithium borohydride (LiBH4) into Mo2N-doped defective boron nitride (Mo2N-DBN) host. Density functional theory (DFT), Ab initio molecular dynamics (MD), and a wide array of experimental data suggested that the Mo2N-DBN host promotes proximity between the active sites of LiBH4, effectively preventing aggregation during sorption processes, thereby leading to a reversible hydrogen storage capacity of 10.80 wt % at 200 °C and 50 bar for LiBH4@Mo2N-DBN composite with minimal loss after five hydrogenation-dehydrogenation cycles. This marked an 84% enhancement over pure LiBH4 under identical conditions and represented the highest reported storage capacity among LiBH4-based composites to date. The Mo2N sites in the composite prevented direct melting transitions of LiBH4 and facilitated the weakening of H-H bonds, which in turn gave rise to fast dehydrogenation kinetics (Ea = 77.44 ± 0.02 kJ/mol). Additionally, analysis of hydrogenation-dehydrogenation energetics indicated that Li atoms are drawn from the LiBH4 cluster toward Mo2N sites, coordinating with N atoms and thereby promoting better interface stability. We anticipate the continuous formation of interfaces between Mo2N-DBN, LiH, and B, where rehydrogenation reactions can proceed efficiently, supported by the migration of H-containing species between bulk and interfacial regions.

Enhanced De/hydrogenation Kinetics and Cycle Stability of Mg/MgH2 by the MnOx-Coated Ti2CTx Catalyst with Optimized Ti-H Bond Stability

MXene based catalysts can significantly enhance hydrogenation and dehydrogenation (de/hydrogenation) kinetics of Mg/MgH2, but they suffer from uncontrollable catalysts-hydrogen bond strength and structural instability. Here, we propose Tx density control of MXene-based catalysts and MnOx coating as a promising solution. The MnOx@Ti2CTx-catalyzed Mg/MgH2 can release 5.97 wt % H2 at 300 °C in 3 min and 5.60 wt % H2 at 240 °C in 15 min with an activation energy of 75.57 kJ·mol-1. In addition, the samples showed excellent de/hydrogenation-cycle stability, and the degradation of hydrogen storage capacity is negligible even after 100 cycles. DFT calculations combined with XPS analysis showed that the Tx defect on the surface of the MnOx@Ti2CTx catalyst could optimize the strength of the Ti-H bond, accelerating both hydrogen dissociation and diffusion processes. The catalyst's surface properties were protected by the MnOx coating, achieving high chemical and catalytic stability. These findings offer a strategy for surface structure optimization and protection of MXene-based catalysts, realizing controllable catalyst-hydrogen bond strength.

Effect of a mesoporous NiCo2O4 urchin-like structure catalyzed with a surface oxidized LiBH4 system for reversible hydrogen storage applications

A mesoporous NiCo2O4 urchin-like structure was synthesized by applying a facile hydrothermal method. Different concentrations of NiCo2O4 urchin-like structures were mixed with a surface oxidized LiBH4 system using a wet-impregnation method, followed by heat treatment. The hydrogen storage capacity of LiBH4 + 25% NiCo2O4, LiBH4 + 50% NiCo2O4 and LiBH4 + 75% NiCo2O4 systems was investigated. Typically, hydrogenated LiBH4 + 25% NiCo2O4, LiBH4 + 50% NiCo2O4 and LiBH4 + 75% NiCo2O4 systems desorbed 2.85 wt%, 3.78 wt% and 3.91 wt% of hydrogen, respectively, at the dehydrogenation temperature ranging from room temperature (RT) to 275 °C. Further, the LiBH4 + 75% NiCo2O4 system exhibited better kinetics than other systems and released ∼5.8 wt% of hydrogen at a isothermal dehydrogenation temperature of 250 °C in 60 minutes. Hydrogen binding energies were calculated as 0.28 eV, 0.27 eV and 0.26 eV for LiBH4 + 25% NiCo2O4, LiBH4 + 50% NiCo2O4 and LiBH4 + 75% NiCo2O4 systems, respectively. Moreover, the calculated activation energies of LiBH4 + 25% NiCo2O4, LiBH4 + 50% NiCo2O4 and LiBH4 + 75% NiCo2O4 systems are 17.99 kJ mol-1, 17.03 kJ mol-1 and 16.92 kJ mol-1, respectively. The calculated BET (Brunauer-Emmett-Teller) surface area of NiCo2O4 and LiBH4 + 75% NiCo2O4 systems is 124.05 and 136.62 m2 g-1, respectively. These results showed that hydrogen sorption and desorption properties are significantly increased by the influence of mesoporous structure, lower binding energy and activation energy of LiBH4 + 75% NiCo2O4 system.

Size Matters: A Computational Study of Hydrogen Absorption in Ionic Liquids

We combined both density functional theory and classical molecular dynamics simulations to investigate the molecular mechanisms governing hydrogen solvation in a total of 12 ionic liquids. Overall, the analysis of the structural properties under high temperature and pressure conditions revealed weak interactions between hydrogen and the ionic liquids, with a slight preference of this gas to be placed at the apolar domains. Interestingly, those ionic liquids comprising nitrate anions allow the accommodation of hydrogen molecules also in the polar areas. The study of the hydrogen velocity autocorrelation functions supports this observation. In addition, the structure of all of the tested ionic liquids was almost insensitive to the addition of hydrogen, so the available free volume and cavity formation are presumably the most important factors affecting solubility.

Paving the Way to the Fuel of the Future-Nanostructured Complex Hydrides

Hydrides have emerged as strong candidates for energy storage applications and their study has attracted wide interest in both the academic and industry sectors. With clear advantages due to the solid-state storage of hydrogen, hydrides and in particular complex hydrides have the ability to tackle environmental pollution by offering the alternative of a clean energy source: hydrogen. However, several drawbacks have detracted this material from going mainstream, and some of these shortcomings have been addressed by nanostructuring/nanoconfinement strategies. With the enhancement of thermodynamic and/or kinetic behavior, nanosized complex hydrides (borohydrides and alanates) have recently conquered new estate in the hydrogen storage field. The current review aims to present the most recent results, many of which illustrate the feasibility of using complex hydrides for the generation of molecular hydrogen in conditions suitable for vehicular and stationary applications. Nanostructuring strategies, either in the pristine or nanoconfined state, coupled with a proper catalyst and the choice of host material can potentially yield a robust nanocomposite to reliably produce H2 in a reversible manner. The key element to tackle for current and future research efforts remains the reproducible means to store H2, which will build up towards a viable hydrogen economy goal. The most recent trends and future prospects will be presented herein.