Developing Ideal Metalorganic Hydrides for Hydrogen Storage: From Theoretical Prediction to Rational Fabrication

Abstract

Materials for hydrogen storage have been extensively explored for a few decades. Thousands of materials have been synthesized and tested; however, few systems could meet the practical requirements. Metalorganic hydrides discovered recently offer new opportunities. It is, however, extremely time-consuming and inefficient to experimentally screen potential materials from a large variety of metal cations and organic anions. In the present study, we performed wide-ranging theoretical predictions and screened more than 90 metalorganic hydrides; 20 of them were identified with both high hydrogen capacities (≥5 wt %) and suitable thermodynamics (heat of H2 desorption: 25–35 kJ/mol-H2) that allow hydrogen uptake and release near ambient condition. We picked up four of them, i.e., Li/Na indolides and 7-azaindolides, for experimental validation. All the four candidates can be easily synthesized via the reactions between the metal hydrides and the corresponding organic precursors. Among them the structures of lithium indolide (P21/c (no. 14)) and sodium 7-azaindolide (P4̅21 c (no. 114) were successfully resolved. Photoelectron spectroscopy and quantum chemical calculations confirmed that the charge density of the organic ring increased with the introduction of an alkali metal, thus optimizing their ΔH d for hydrogen storage. Importantly, we demonstrated experimentally that lithium indolide with a theoretical hydrogen capacity of 6.1 wt % has a heat of hydrogen absorption of ca. 33.7 kJ/mol-H2 which is in excellent agreement with the value (33.6 kJ/mol-H2) predicted theoretically. The partially reversible hydrogen release and uptake can be can be achieved at the temperature as low as 100 °C. These results illustrate the great potential of metalorganic hydrides for tackling the grand challenge of hydrogen storage and manifest the effectiveness of theoretical prediction in guiding materials fabrication.

Fabrication of Lithium Indolide and Derivates for Ion Conduction

“…The crystal structure of Li-ID was determined in our very recent study . It crystallizes in a monoclinic structure with the space group of P 2 1 /c (No.…”

“…The crystal structure of Li-ID was determined in our very recent study. 41 It crystallizes in a monoclinic structure with the space group of P2 1 /c (No. The crystal structure of Li-ID-2THF was first solved by singlecrystal XRD at 100 K. The XRD pattern collected from the crushed single-crystal sample at room temperature (Figure S2) agrees well with that of powder sample synthesized by the ball-milling method (Figure 1a).…”

“…Very recently, we developed a type of materials for hydrogen storage, namely, metalorganic compounds, which spans across the domain of inorganic and organic hydrogenous compounds and exhibits ideal thermodynamic properties for hydrogen storage. It is worth mentioning that these metalorganic compounds possess large anions (such as phenoxide, indolide, and carbazolide anions) as well as layered crystal structures, which are prerequisites for fast ionic conductors in some cases. Inspired by the research above, lithium indolide and its THF-coordinated derivates are rationally fabricated and employed for ion conduction in the present study.…”

Enhancing the cycling stability of MgH2 using nitrogen modified titanate

“…1,2 However, the safe, efficient and economical transportation and storage of hydrogen have been a bottleneck for its practical applications. 3 To overcome this challenge, various hydrogen storage solutions were developed, such as solid-state materials, 4 physical adsorption materials, 5 liquid organic hydrogen carriers 6 and so on. The large hydrogen capacity of MgH 2 (theoretically up to 7.6 wt% and 110 kg m − 3 ), along with abundance, reversibility, and non-toxicity make it one of the most attractive choices for solid-state hydrogen storage.…”

Realizing room temperature catalytic hydrogenation of sodium phenoxide by Ru/TiO2 for hydrogen storage

“…1 Recently, we proposed a new family of hydrogen storage materials, which spans across the domains of organic and inorganic hydrides with ideal thermodynamic properties for dehydrogenation, namely metalorganic hydrides. In these materials, alkali or alkaline earth metals were adopted to replace the protic H atom in organic hydrides, [2][3][4][5] where the thermodynamics of newly developed materials have been improved substantially. Among the metalorganic hydrides, sodium phenoxide is considered one of the promising candidates, thanks to its high hydrogen capacity, low cost, ease of synthesis, and good stability in air and water.…”