Catalytic Tuning of Sorption Kinetics of Lightweight Hydrides: A Review of the Materials and Mechanism

Abstract

Hydrogen storage materials have been a subject of intensive research during the last 4 decades. Several developments have been achieved in regard of finding suitable materials as per the US-DOE targets. While the lightweight metal hydrides and complex hydrides meet the targeted hydrogen capacity, these possess difficulties of hard thermodynamics and sluggish kinetics of hydrogen sorption. A number of methods have been explored to tune the thermodynamic and kinetic properties of these materials. The thermodynamic constraints could be resolved using an intermediate step of alloying or by making reactive composites with other hydrogen storage materials, whereas the sluggish kinetics could be improved using several approaches such as downsizing and the use of catalysts. The catalyst addition reduces the activation barrier and enhances the sorption rate of hydrogen absorption/desorption. In this review, the catalytic modifications of lightweight hydrogen storage materials are reported and the mechanism towards the improvement is discussed.

Superior Hydrogen Sorption Kinetics of Ti0.20Zr0.20Hf0.20Nb0.40 High-Entropy Alloy

“…In Formula (3) [49,50], A is the factor and E a is the performance activation energy (kJ/mol) of the hydrogen absorption reaction. The slope of the fitting line of these four points is calculated to show the activation energy of hydrogen absorption reaction (E a ) of hydrogenated Ti 0.20 Zr 0.20 Hf 0.20 Nb 0.40 is −4.37 kJ/mol.…”

“…The specific values for hydrogen absorption equilibrium pressure and equilibrium hydrogen storage capacity are shown in Table3.With reference to metals and alloys, the hydrogen storage process steps include physisorption, chemisorption, surface penetration, diffusion and hydride formation[49]. Apart from the first step (i.e., physisorption), other steps can be rate-limiting and influence the kinetics of hydrogen sorption[50]. Each hydrogen absorption kinetic step has its corresponding kinetic model[51,52].…”

Factors Affecting Hydrogen Adsorption in Metal–Organic Frameworks: A Short Review

“…An ultimate system objective in 2020 for automobile fueling was set by the U.S. Department of Energy (DoE) at ~7 wt% hydrogen by weight [ 8 ]. Various materials have been studied in this respect, e.g., metal hydride systems [ 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 ]; however, numerous problems are associated with the use of high-temperature H 2 storage materials (interstitial and complex metal hydrides or their reactive hydride composites), namely, their high cost, low specific uptake by weight, unfavorable kinetics requiring heating cycles, and susceptibility to contamination by impurities. In addition, various carbon-based adsorbents (carbon black, intercalated graphite, carbon nanotubes, and nanoporous polymer networks) have been widely studied and categorized as low temperature H 2 storage materials, although they have been subject to ambiguous results [ 19 , 20 , 21 , 22 , 23 , 24 , 25 , 26 , 27 ].…”

Synthesis of Highly Activated Magnesium by Niobium and Tantalum Gel Oxide Catalyst

“…There are various types of hydrogen storage materials, such as conventional metal, complex, and chemical hydrides, as well as liquid organic materials. 3,4) Various types of intermetallic compounds have been developed for stationary applications. However, low hydrogen storage capacity, high material cost, and heavy weight prohibit the mobile application of intermetallic compounds.…”