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Hydrolysis of Mg-based materials is considered as a potential means of safe and convenient real-time control of H 2 release, enabling efficient loading, discharge and utilization of hydrogen in portable electronic devices. At present work, the hydrogen generation properties of MgLi-graphite composites were evaluated for the first time. The MgLi-graphite composites with different doping amounts of expanded graphite (abbreviated as EG hereinafter) were synthesized through ball milling and the hydrogen behaviors of the composites were investigated in chloride solutions. Among the above doping systems, the 10 wt.% EG-doped MgLi exhibited the best hydrogen performance in MgCl 2 solutions. In particular, the 22 h-milled MgLi-10 wt.% EG composites possessed both desirable hydrogen conversion and rapid reaction kinetics, delivering a hydrogen yield of 966 mL H 2 g−1 within merely 2 min and a maximum hydrogen generation rate of 1147 mL H 2 min−1 g−1, as opposed to the sluggish kinetics in the EG-free composites. Moreover, the EG-doped MgLi showed superior air-stable ability even under a 75 RH% ambient atmosphere. For example, the 22 h-milled MgLi-10 wt.% EG composites held a fuel conversion of 89% after air exposure for 72 h, rendering it an advantage for Mg-based materials to safely store and transfer in practical applications. The similar favorable hydrogen performance of MgLi-EG composites in (simulate) seawater may shed light on future development of hydrogen generation technologies. [ABSTRACT FROM AUTHOR]

Sodium borohydride (NaBH4) is regarded as an excellent hydrogen-generated material, but its irreversibility of hydrolysis and high cost of regeneration restrict its large-scale application. In this study a convenient and economical method for NaBH4 regeneration is developed for the first time without hydrides used as starting materials for the reduction process. The real hydrolysis by-products (NaBO2 ·2H2O and NaBO2 ·4H2O), instead of dehydrated sodium metaborate (NaBO2), are applied for the regeneration of NaBH4 with Mg at room temperature and atmospheric pressure. Therefore, the troublesome heat-wasting process to obtain NaBO2 using a drying procedure at over 350 °C from NaBO2 · xH2O is omitted. Moreover, the highest regeneration yields of NaBH4 are achieved to date with 68.55% and 64.06% from reaction with NaBO2 ·2H2O and NaBO2 ·4H2O, respectively. The cost of NaBH4 regeneration shows a 34-fold reduction compared to the previous study that uses MgH2 as the reduction agent, where H2 is obtained from a separate process. Furthermore, the regeneration mechanism of NaBH4 is clarified and the intermediate compound, NaBH3(OH), is successfully observed for the first time during the regeneration process. [ABSTRACT FROM AUTHOR]

This paper reported the performance and mechanism of hydrogen generation via hydrolysis of ball-milled Mg-Mg 2 Si composite (5.3 wt % Si-94.7 wt % Mg) in deionized water and in MgCl 2 solution. The results showed that the obtained Mg-Mg 2 Si composite presented relatively higher hydrogen generation performance than pure magnesium. Adoption of 0.5 M MgCl 2 solution to replace deionized water sufficiently and vastly enhanced the hydrolysis properties of the Mg-Mg 2 Si composite. The composite in 0.5 M MgCl 2 solution generated 445 mL/g hydrogen in 5 min, 688 mL/g hydrogen in 10 min and 889 mL/g hydrogen (conversion rate 99%) in 40 min at 328 K. This remarkable improvement is due to that the addition of Si element in the composite and the introduction of MgCl 2 in solution, as well as the special preparation process of the materials, could decrease the formation of continuous magnesium hydroxide passive layer on the particle surface, directly or indirectly. Moreover, the apparent activation energies for composite hydrolysis in deionized water, in 0.5 and 2.0 M MgCl 2 solution were calculated to be 30.1 ± 0.6, 9.5 ± 0.1 and 3.7 ± 0.2 kJ/mol, respectively. This work demonstrates that the hydrogen generation system based on low-cost and high-performance Mg-Mg 2 Si composite is very applicable and promising; and it may open a new avenue for onsite hydrogen supply. [ABSTRACT FROM AUTHOR]

In this work, flower-like MoS 2 spheres are synthesized via a hydrothermal method and the catalytic activity of the as-prepared and bulk MoS 2 on hydrolysis of Mg is systematically investigated for the first time. The Mg-MoS 2 composites are prepared by ball milling and the hydrogen generation performances of the composites are investigated in 3.5% NaCl solution. The experimental results suggest that the as-prepared MoS 2 exhibits better catalytic effect on hydrolysis of Mg compared to bulk MoS 2 . In particular, Mg-10 wt% MoS 2 (as-prepared) composite milled for 1 h shows the best hydrogen generation properties and releases 90.4% of theoretical hydrogen generation capacity within 1 min at room temperature. The excellent catalytic effect of as-prepared MoS 2 may be attributed to the following aspects: three-dimensional flower-like MoS 2 architectures improve its dispersibility on Mg particles; make the composite more reactive; hamper the generated Mg(OH) 2 from adhering to the surface of Mg; and increase the galvanic corrosion of Mg. In addition, a hydrogen generator based on the hydrolysis reaction of Mg-0.2 wt% MoS 2 composite is manufactured and it can supply a maximum hydrogen flow rate of 2.5 L/min. The findings here demonstrate the as-prepared flower-like MoS 2 can be a promising catalyst for hydrogen generation from Mg. [ABSTRACT FROM AUTHOR]

Hydrolysis of materials in water can be a promising solution of onsite hydrogen generation for realization of hydrogen economy. In this work, it was the first time that the MgH 2 -LiNH 2 composites were explored as air-stable hydrolysis system for hydrogen generation. The MgH 2 -LiNH 2 composites with different composition ratios were synthesized by ball milling with various durations and the hydrogen generation performances of the composite samples were investigated and compared. X-ray diffraction, X-ray photoelectron spectroscopy and scanning electron microscopy techniques were adopted to elucidate the performance improvement mechanisms. The hydrolysis properties of MgH 2 were found to be significantly enhanced by the introduction of LiNH 2 . The 4MgH 2 -LiNH 2 composite ball milled for 5 h can generate 887.2 mL g −1 hydrogen in 1 min and 1016 mL g −1 in 50 min, one of the best results so far for Mg based hydrolysis materials. The LiOH·H 2 O and NH 4 OH phases of hydrolysis products from LiNH 2 may prevent formation of Mg(OH) 2 passivation layer on the surface and supply enough channels for hydrolysis of MgH 2 . The MgH 2 -LiNH 2 composites appeared to be very stable in air and no obvious negative effect on kinetics and hydrogen generation yield was observed. These good performances demonstrate that the studied MgH 2 -LiNH 2 composites can be a promising and practicable hydrogen generation system. [ABSTRACT FROM AUTHOR]

LiBH 4 (LB in short) with a hydrogen capacity as high as 18.5 wt% and a low molecular weight (21.78 g mol−1) is among the most promising candidates for the hydrogen-based economy. However, current major technologies in (re)generation of LB rely heavily on energy-intensive processes, which greatly prohibits practical scaling-up of applications. Here we report a sustainable and effective approach to (re)generate LB via converting renewable H+ in crystalline water into H-, achieving a desirable yield of ∼50%. This one-step synthesis method relies on the reaction between spent fuels, specifically LiBO 2 · x H 2 O, and Mg-based alloys to form LB under ambient atmosphere. Notably, our approach surpasses the efficiency of other conventional method, such as LiH-B-H 2 and MgH 2 -LiBO 2 systems, which not only bypasses the energy-intensive dehydration procedure of LiBO 2 · x H 2 O (∼470 ℃) but also eliminates the use of costly hydrides or high-pressure H 2. Our findings indicate that Mg participated in the regeneration process prior to Al in Mg-Al alloys and [BH 4 ]- is gradually evolved from other intermediate species [BH x (OH) 4- x ]- (x = 0, 1, 2, 3). By combining hydrogen release and efficient storage of hydrogen-rich substrate in a closed materials cycle, this study may shed light on a promising step toward application of renewable hydrogen in a fuel cell-based hydrogen economy. • A hydrogen cycle with the couple hydrolysis and regeneration of LiBH 4 is achieved in the present work. • The regeneration technology for LiBH 4 is not only energy and cost effective, but also circumvents the need for troublesome heat-wasting procedures and expensive hydrides. • The regeneration yield of LiBH 4 is 50%, sourcing its essential hydrogen from renewable water. • The study demonstrates the universal applicability of regenerating LiBH 4 through the utilization of Mg-based reducing agents and LiBO 2 · x H 2 O. [ABSTRACT FROM AUTHOR]

Lithium borohydride (LiBH 4) has received much attention due to its high hydrogen density of 18.5 wt%. However, in the hydrolytic process for hydrogen supply, the sluggish kinetics of LiBH 4 and the agglomeration of by-product greatly limit its wide utilization. In this work, transition-metal chlorides (CoCl 2 , NiCl 2 , FeCl 3) are firstly adopted to explore the hydrogen liberation behaviors of LiBH 4. The hydrolysis kinetics can be well-controlled by tuning the concentration of chlorides. Among the above chlorides, CoCl 2 displays much faster reaction kinetics, delivering a hydrogen generation rate ranging from 421 to 41701 mL min−1 g−1 with a maximum conversion of 95.3%, much higher than the value of 225 mL min−1 g−1 H 2 with Pt–LiCoO 2. The maximum gravimetric hydrogen density may reach 8.7 wt% at H 2 O/LiBH 4 = 2–6 mol/mol. Furthermore, NH 3 is introduced to solve the issue of uncontrollable kinetics of LiBH 4 by forming its ammoniates, where LiBH 4 ·NH 3 catalyzed by CoCl 2 could stably release over 4350 mL g−1 H 2 per unit weight of LiBH 4 within 30 min at 40 °C, with a hydrogen density of ∼7.1 wt% and a hydrogen yield of 97.0%. Our approaches adopting non-noble metal chlorides are efficient and affordable for hydrogen supply to PEMFCs via hydrolysis of LiBH 4 -based materials. • LiBH 4 -based materials catalyzed by non-noble metal chlorides are investigated for the first time. • The gravimetric hydrogen density of LiBH 4 hydrolysis may reach 8.7 wt%. • The hydrolysis kinetics of LiBH 4 could be well-controlled by CoCl 2 solution. • The conversion yield of LiBH 4 ·NH 3 nearly reaches 97% with a gravimetric hydrogen density of ∼7.1 wt%. • The catalytic effect of CoCl 2 is better than NiCl 2 or FeCl 3.. [ABSTRACT FROM AUTHOR]

Onsite hydrogen generation by sodium borohydride hydrolysis resolves hydrogen energy supply system challenges. However, the spent-NaBH 4 regeneration is still a problem in the closed loop of this irreversible reaction. As the by-product is the key to the problem, NaB(OH) 4 is regarded as not the boron source but the hydrogen source of NaBH 4 regeneration. Therefore, in this study, inexpensive Al metal and NaB(OH) 4 are ball milled under argon to regenerate NaBH 4 without additional hydrogen input. However, the ball-milling reaction is hindered by the flexible Al and impact oxide layer, and the NaBH 4 yield is only approximately 22 %. Therefore, a brittle intermetallic compound Mg 2 Al 3 is reacted with NaB(OH) 4 by ball milling, achieving a NaBH 4 yield of over 42 %. The mechanism study shows that the brittleness of the raw material plays an important role in promoting the ball-milling reaction. This study achieves NaBH 4 regeneration using only Al as the reducing agent and provides a promising method to promote the mechanochemical regeneration of NaBH 4. • NaBH 4 regeneration was achieved using only Al as the reducing agent. • Ball milled Mg 2 Al 3 and NaB(OH) 4 achieved the highest NaBH 4 yield of 42 %. • Brittle reducing agent enhances the ball-milled regeneration of NaBH 4. [ABSTRACT FROM AUTHOR]

Sodium borohydride (NaBH 4) is considered to be an excellent hydrogen-generation material via hydrolysis. However, it remains challenge to regenerate it after hydrolysis in practical applications. Therefore, a low-cost regeneration method from hydrolysis by-products for recycling is the key issue. In this study, NaBH 4 was successfully regenerated by direct high-energy ball milling of magnesium alloy (Mg 17 Al 12) and hydrolysis by-product NaBO 2 ·2H 2 O with addition of a small amount of NaH. Notably, unlike traditional method, here there is no need of adding extra hydrogen and the H− in the regenerated NaBH 4 is mainly from the H+ in the coordinated water. It was found that through adding a small amount of NaH, the highest yield may reach 57% after optimizing the regeneration process. In addition, it is the first time we found that not only Mg can participate in the reaction, but also Al; and the addition of NaH can promote the reaction. Furthermore, the regeneration mechanism of NaBH 4 was analyzed and the transition pattern [B(OH) 4 ]−/[BH 3 (OH)]−/[BH 4 ]− was successfully observed during the regeneration process. It is worth emphasizing that NaBH 4 can be regenerated through ball milling method, which is energy-saving and suitable for up-scaling in the future. • A low-cost method for NaBH 4 regeneration was developed by Mg-Al alloy. • Using the hydrolysis by-products (NaBO 2 ·2H 2 O) as raw material to regenerate NaBH 4. • A small amount of NaH can significantly improve the yield of NaBH 4. • The mechanism of NaBH 4 regeneration is revealed, not only Mg can participate in the reaction, but also Al. [ABSTRACT FROM AUTHOR]

Abstract The possibility of hydrogen generation by hydrolysis of magnesium borohydride and its ammoniates was explored. Results show that catalyst-free Mg(BH 4) 2 can generate 1700 mL (H 2)·g−1 in 1 min, 2760 mL (H 2)·g−1 in 2 h, and 3004 mL (H 2)·g−1 in 5 h without any diborane (B 2 H 6) emission. Mg(BH 4) 2 presents the highest hydrogen yield reported to date. However, the hydrogen generation rate of Mg(BH 4) 2 may be too fast to be controllable in some hydrogen production cases. Therefore, NH 3 was added to form ammoniates to further regulate the hydrogen supply kinetics of Mg(BH 4) 2. The hydrogen yields of Mg(BH 4) 2 ·0.5NH 3 , Mg(BH 4) 2 ·NH 3 , Mg(BH 4) 2 ·2NH 3 , Mg(BH 4) 2 ·3NH 3 and Mg(BH 4) 2 ·6NH 3 are 2376, 2029, 1780, 1665 and 1180 mL (H 2) g−1, respectively, which demonstrates a well-controlled hydrogen supply rate. These results indicate that catalyst-free Mg(BH 4) 2 and its ammoniates have good hydrolysis performance and show promise as convenient high-density hydrogen generation materials. Highlights • Mg(BH 4) 2 demonstrates presents the highest yield reported to date. • The hydrolysis kinetics of Mg(BH 4) 2 can be controlled by introduction of ammonia. • The introduction of ammonia can improve oxidation resistance of Mg(BH 4) 2. [ABSTRACT FROM AUTHOR]

Apparent activation energies of MgH 2 hydrolysis in deionized water were deduced for the first time being 58.06 kJ/mol. This paper also reports the mechanisms of MgH 2 hydrolysis and the effects of NH 4 Cl on the kinetics of magnesium hydride hydrolysis. Experimental results show that hydrogen generation via MgH 2 hydrolysis exhibited the highest rates in 4.50 wt% NH 4 Cl solution. This is because addition of NH 4 Cl could effectively decrease the compactness of magnesium hydroxide. It is also found that addition of NH 4 Cl could effectively enhance the hydrolysis kinetics and lead to a reduction of the apparent activation energy of MgH 2 hydrolysis. The apparent activation energies of MgH 2 hydrolysis decreased from 58.06 kJ/mol in deionized water to 50.86 and 30.37 kJ/mol in 0.5 and 4.5 wt% NH 4 Cl solutions, respectively. MgH 2 -4.5 wt% NH 4 Cl system showed the fastest hydrolysis rate, producing 1310 mL g −1 hydrogen in 5 min, 1604 mL g −1 hydrogen in 10 min, and 1660 mL g −1 hydrogen in 30 min at 60 °C. The results reveal that NH 4 Cl may be a promising reagent for promoting the hydrolysis of MgH 2 for hydrogen generation systems, which demonstrated a new method to improve the hydrolysis of MgH 2 . [ABSTRACT FROM AUTHOR]

Currently, economic hydrogen production is the key issue preventing the application of the hydrogen as the energy carrier for global low-carbon and ever-increasing energy challenges. Hydrogen generation by spontaneous hydrolysis reaction of light metal-based materials including Mg, Al and NaBH 4 , is a promising method integrating safe storage and effective supply of hydrogen. However, these hydrolytic materials are still plagued by sluggish hydrogen kinetics and low H 2 yield, owing to the formation of the surface passivation layers. While numerous strategies such as refining material's structure, compositing with other materials, alloying and modifying aqueous solutions, have been proposed to enhance hydrogen generation performance, the high cost caused by irreversibility hinders the large-scale application. Therefore, low cost regeneration of materials from hydrolytic byproduct is essential for hydrogen generation via hydrolysis. Herein, this review presents the recent research progress on above topics as well as their application in fuel cells. The future challenges and opportunities in this area are also described. [Display omitted] • A overview in hydrogen generation from the hydrolysis of light metal-based materials is introduced systematically. • The effective regeneration technologies of light metal-based materials from their hydrolytic byproducts are delivered in detail. • The application of hydrolytic hydrogen production systems in fuel cells is discussed briefly. • The challenges and opportunities associated with hydrogen generation from light metal-based materials are described. [ABSTRACT FROM AUTHOR]