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We present the research findings of the DOE-funded Hydrogen Storage Engineering Center of Excellence (HSECoE) related to liquid-phase and slurry-phase chemical hydrogen storage media and their potential as future hydrogen storage media for automotive applications. Chemical hydrogen storage media other than neat liquid compositions will prove difficult to meet the DOE system level targets. Solid- and slurry-phase chemical hydrogen storage media requiring off-board regeneration are impractical and highly unlikely to be implemented for automotive applications because of the formidable task of developing solid- or slurry-phase transport systems that are commercially reliable and economical throughout the entire life cycle of the fuel. Additionally, the regeneration cost and efficiency of chemical hydrogen storage media is currently the single most prohibitive barrier to implementing chemical hydrogen storage media. Ideally, neat liquid-phase chemical hydrogen storage media with net-usable gravimetric hydrogen capacities of greater than 7.8 wt% are projected to meet the 2017 DOE system level gravimetric and volumetric targets. The research presented herein is a collection of research findings that do not in and of themselves warrant a dedicated manuscript. However, the collection of results do, in fact, highlight the engineering challenges and short-comings in scaling up and demonstrating fluid-phase ammonia borane and alane compositions that all future materials researchers working in hydrogen storage should be aware of.

Herein we demonstrate the use of ethylenediamine bisborane (EDAB) as a suitable hydrogen source for transfer hydrogenation reactions on C-C double bonds mediated by metal nanoparticles. Moreover, EDAB also acts as a reducing agent for carbonyl functionalities in water under metal-free conditions.

Development of low-cost and high-performance catalysts for hydrogen generation via hydrolysis of ammonia borane (NH 3 BH 3 , AB) is a highly desirable pathway for future hydrogen utilization. In this work, Ni nanocatalysts doped with CeO x and supported on graphene (Ni-CeO x /graphene) were synthesized via a facile chemical reduction route and applied as robust catalysts for the hydrolysis of AB in aqueous solution at room temperature. The as-synthesized Ni-CeO x /graphene nanocomposites (NCs) exhibited excellent catalytic activity with a turnover frequency (TOF) as high as 68.2 min −1 , which is 49-fold higher than that for a simple Ni nanoparticle catalyst and is among the highest values reported for non-noble metal catalysts in AB hydrolysis. The development of efficient and low-cost Ni-CeO x /graphene catalysts enhances the feasibility of using ammonia borane as a chemical hydrogen storage material, which may find application ina hydrogen fuel-cell based economy.

Ammonia borane (NH 3 BH 3 , AB) holds promise for chemical storage of hydrogen. However, designing superb and low-cost photocatalyst to drive hydrogen evolution from AB under visible light irradiation is highly desirable but remains a major challenge for promoting the practical utilization of AB. Herein, we demonstrated a heterostructure photocatalyst consisting of zero-dimensional (0D) CoP nanoparticles immobilized on two-dimensional (2D) Co 2 P nanosheets (CoP/Co 2 Ps) as a high-performance and low-cost catalyst for hydrogen evolution from AB hydrolysis, in which 0D/2D heterostructure was synthesized using the salt-induced phase transformation strategy. Interestingly, the optimized CoP/Co 2 Ps exhibit a robust H 2 evolution rate of 32.1 L·min −1 ·g Co −1 , corresponding to a turnover frequency (TOF) value of 64.1 min −1 , being among the highest TOF for non-noble-metal catalysts ever reported, even outperforming some precious metal catalysts. This work not only opens a new avenue to accelerate hydrogen evolution from AB by regulating the electronic structures of heterointerfaces, but also provides a novel strategy for the construction of precious-metal-free materials for hydrogen-related energy catalysis in the future.

Ammonia borane (AB), a liquid hydrogen storage material, has attracted increasing attention for hydrogen utilization because of its high hydrogen content. However, the slow kinetics of AB hydrolysis and the indefinite catalytic mechanism remain significant problems for its large‐scale practical application. Thus, the development of efficient AB hydrolysis catalysts and the determination of their catalytic mechanisms are significant and urgent. A summary of the preparation process and structural characteristics of various supported catalysts is presented in this paper, including graphite, metal‐organic frameworks (MOFs), metal oxides, carbon nitride (CN), molybdenum carbide (MoC), carbon nanotubes (CNTs), boron nitride (h‐BN), zeolites, carbon dots (CDs), and metal carbide and nitride (MXene). In addition, the relationship between the electronic structure and catalytic performance is discussed to ascertain the actual active sites in the catalytic process. The mechanism of AB hydrolysis catalysis is systematically discussed, and possible catalytic paths are summarized to provide theoretical considerations for the designing of efficient AB hydrolysis catalysts. Furthermore, three methods for stimulating AB from dehydrogenation by‐products and the design of possible hydrogen product‐regeneration systems are summarized. Finally, the remaining challenges and future research directions for the effective development of AB catalysts are discussed. A summary of the preparation process and structural characteristics of supported catalysts is presented. The mechanism and catalytic paths of ammonia borane (AB) hydrolysis are discussed for the designing of AB hydrolysis catalysts. Methods for stimulating AB from dehydrogenation by‐products and hydrogen product‐regeneration systems are summarized. The remaining challenges and future directions for the effective development of AB catalysts are discussed.

The solvolysis of ammonia borane (AB) and the hydrogenation of nitroarenes represent significant reactions for hydrogen generation and value-added chemical synthesis. The strategic engineering of the catalysts is imperative for surmounting obstacles associated with their stability and catalytic efficiency. In this work, subnanometric bimetallic Pt–Pd clusters were encapsulated within silicalite-1 (S-1) zeolites through a ligand-protected in-situ hydrothermal synthesis method. The synergetic effect of bimetallic composition and zeolite confinement markedly enhances the catalytic performance of representative Pt 0.5 Pd 0.5 @S-1-H catalyst, affording exceptional turnover frequency (TOF) values of 1,043 and 573 mol H2 mol metal −1 min −1 for AB hydrolysis and methanolysis at ambient conditions, respectively, surpassing most of the state-of-the-art Pt-based catalysts. Kinetic and isotopic experiments reveal that the bimetallic catalytic system remarkably boosts the O–H cleavage of water, thereby facilitating the H 2 production from AB hydrolysis. Remarkably, a conspicuous synergistic effect is demonstrated in the shape-selective tandem hydrogenation of nitroarenes, with the bimetallic catalyst facilitating both AB hydrolysis and nitroarene hydrogenation, giving a high TOF value of 1,260 h −1 under atmospheric pressure. This study not only demonstrates the effectiveness of bimetallic nanocatalysts encapsulated in zeolites for hydrogen production from chemical hydrogen storage materials, but also paves the way for the design of catalysts with multifunctional active sites capable of synergistically promoting tandem catalytic processes.

Rational construction of highly dispersed, small size, and low cost catalysts for release of hydrogen from ammonia borane (AB) is regarded as a prospective approach for promoting the development of upcoming hydrogen economy. However, the high price and scarcity of precious metal catalysts impose restrictions on their large-scale application. To this end, with the aid of a Cu doped CoZn-zeolitic imidazolate frameworks (ZIFs) template strategy, we successfully construct ultrafine monodispersed Co 2 P/(0.59-Cu 3 P) on CoZn-ZIF derived porous N-doped carbon (Co 2 P/(0.59-Cu 3 P)-NC) as an efficient non-noble-metal catalyst. Specifically, Co and Cu atoms can be geometrically separated to high degree due to the presence of Zn in the CuCoZn-ZIF precursor, and evaporation of Zn during pyrolysis can generate porous structure with the framework well maintained. The results show that porous Co 2 P/(0.59-Cu 3 P)-NC bimetallic phosphide exhibits large specific surface area, hierarchical pore structure, and well-exposed active sites. Based on the kinetics analyses and ion effects, the catalyst has achieved an unprecedentedly high total turnover frequency (TOF) of 798 mol H 2 ⋅ mol cat − 1 ⋅ min − 1 in 0.4 M NaOH solution at 298 K, which surpasses all the ever-reported transition-metal phosphides catalysts for hydrogen generation from AB. Experiments and theoretical studies confirm that the highly porous structure of the support, the ultrafine and high dispersion of nanoparticles, and the N/P doping and their synergistic effects (e.g., M-P, M-N, N-C, M-M’, and M-support) jointly induce strong electron transfer, which can reduce the reaction energy barrier and enhance their interaction with AB, thus correspondingly obtaining excellent catalytic performance. The mechanism and strategy presented in this work pave an avenue for the design of non-noble metal catalyst for hydrogen energy system.

Platinum and ruthenium nanoparticles stabilised by an amine modified polymer immobilised ionic liquid (MNP@NH 2 -PEGPIILS, M = Pt, Ru) catalyse the hydrolytic liberation of hydrogen from dimethylamine borane (DMAB), ammonia borane (AB) and NaBH 4 under mild conditions. While RuNP@NH 2 -PEGPIILS and PtNP@NH 2 -PEGPIILS catalyse the hydrolytic evolution of hydrogen from NaBH 4 with comparable initial TOFs of 6,250 molesH 2 .molcat −1 .h −1 and 5,900 molesH 2 .molcat −1 .h −1 , respectively, based on the total metal content, RuNP@NH 2 -PEGPIILS is a markedly more efficient catalyst for the dehydrogenation of DMAB and AB than its platinum counterpart, as RuNP@NH 2 -PEGPIILS gave initial TOFs of 8,300 molesH 2 .molcat −1 .h −1 and 21,200 molesH 2 .molcat −1 .h −1 , respectively, compared with 3,050 molesH 2 .molcat −1 .h −1 and 8,500 molesH 2 .molcat −1 .h −1 , respectively, for PtNP@NH 2 -PEGPIILS. Gratifyingly, for each substrate tested RuNP@NH 2 -PEGPIILS and PtNP@NH 2 -PEGPIILS were markedly more active than commercial 5wt % Ru/C and 5wt% Pt/C, respectively. The apparent activation energies of 55.7 kJ mol −1 and 27.9 kJ mol −1 for the catalytic hydrolysis of DMAB and AB, respectively, with RuNP@NH 2 -PEGPIILS are significantly lower than the respective activation energies of 74.6 kJ mol −1 and 35.7 kJ mol −1 for its platinum counterpart, commensurate with the markedly higher initial rates obtained with the RuNPs. In comparison, the apparent activation energies of 44.1 kJ mol −1 and 46.5 kJ mol −1 , for the hydrolysis NaBH 4 reflect the similar initial TOFs obtained for both catalysts. The difference in apparent activation energies for the hydrolysis of DMAB compared with AB also reflect the higher rates of hydrolysis for the latter. Stability and reuse studies revealed that RuNP@NH 2 -PEGPIILS recycled efficiently as high conversions for the hydrolysis of DMAB were maintained across five runs with the catalyst retaining 97% of its activity. Graphical Abstract

The liquid chemical hydrogen storage technology has great potentials for high-density hydrogen storage and transportation at ambient temperature and pressure. However, its commercial applications highly rely on the high-performance heterogeneous dehydrogenation catalysts, owing to the dehydrogenation difficulty of chemical hydrogen storage materials. In recent years, the chemists and materials scientists found that the supported metal nanoparticles (MNPs) can exhibit high catalytic activity, selectivity, and stability for the dehydrogenation of chemical hydrogen storage materials, which will clear the way for the commercial application of liquid chemical hydrogen storage technology. This review has summarized the recent important research progress in the MNP-catalyzed liquid chemical hydrogen storage technology, including formic acid dehydrogenation, hydrazine hydrate dehydrogenation and ammonia borane dehydrogenation, discussed the urgent challenges in the key field, and pointed out the future research trends.

Interest in chemical hydrogen storage has increased, because the supply of fossil fuels are limited and the harmful effects of burning fossil fuels on the environment have become a focus of public concern. Hydrogen, as one of the energy carriers, is useful for the sustainable development. However, it is widely known that controlled storage and release of hydrogen are the biggest barriers in large-scale application of hydrogen energy. Ammonia borane (NH3BH3, AB) is deemed as one of the most promising hydrogen storage candidates on account of its high hydrogen to mass ratio and environmental benignity. Development of efficient catalysts to further improve the properties of chemical kinetics in the dehydrogenation of AB under appropriate conditions is of importance for the practical application of this system. In previous studies, a variety of noble metal catalysts and their supported metal catalysts (Pt, Pd, Au, Rh, etc.) have presented great properties in decomposing the chemical hydride to generate hydrogen, thus, promoting their application in dehydrogenation of AB is urgent. We analyzed the hydrolysis of AB from the mechanism of hydrogen release reaction to understand more deeply. Based on these characteristics, we aimed to summarize recent advances in the development of noble metal catalysts, which had excellent activity and stability for AB dehydrogenation, with prospect towards realization of efficient noble metal catalysts.