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HighlightsAn overview of the recent advances in hydrogen production from light metal-based materials is presented, including hydrolysis of Mg-based alloys and hydrides, hydrolysis of Al-based alloys and hydrides and (catalyzed) hydrolysis/alcoholysis of borohydrides.Hydrogen production and storage in a close loop are achieved via hydrolysis and regeneration of borohydrides, demonstrating a promising step toward the large-scale application of chemical hydrogen storage materials in a fuel cell-based hydrogen economy.As an environmentally friendly and high-density energy carrier, hydrogen has been recognized as one of the ideal alternatives for fossil fuels. One of the major challenges faced by “hydrogen economy” is the development of efficient, low-cost, safe and selective hydrogen generation from chemical storage materials. In this review, we summarize the recent advances in hydrogen production via hydrolysis and alcoholysis of light-metal-based materials, such as borohydrides, Mg-based and Al-based materials, and the highly efficient regeneration of borohydrides. Unfortunately, most of these hydrolysable materials are still plagued by sluggish kinetics and low hydrogen yield. While a number of strategies including catalysis, alloying, solution modification, and ball milling have been developed to overcome these drawbacks, the high costs required for the “one-pass” utilization of hydrolysis/alcoholysis systems have ultimately made these techniques almost impossible for practical large-scale applications. Therefore, it is imperative to develop low-cost material systems based on abundant resources and effective recycling technologies of spent fuels for efficient transport, production and storage of hydrogen in a fuel cell-based hydrogen economy.

The hydrolysis/methanolysis of silicon has received considerable attention to achieve efficient and on-demand hydrogen conversion. However, the intense covalent network and highly localized electrons in pure Si impede its reactivity with water (H 2 O) or methanol (CH 3 OH), thereby hindering the hydrogen release. In this work, we report the synthesis of Zintl phase alkalis-Si alloys via simple ball-milling or sintering, showing eminent performance in enhancement of H 2 O/CH 3 OH dissociation. Experiments combined with DFT calculations have revealed that the obtained Zintl phase alloys exhibit discrete Si clusters containing well-defined unpaired electrons that efficiently facilitate the interaction between reductant and solvent molecules. Such an effect thereby reduces the activation barrier of H 2 O/CH 3 OH dissociation to yield active intermediates containing Si-H structure, which significantly promotes the hydrogen release with favorable kinetics and efficiency. The optimal Zintl Li 21 Si 5 alloy achieves ultrahigh Si utilization rates of 86.9% in water and 98.1% in methanol at 25 °C, respectively. Remarkably, even at an extremely low temperature of −40 °C, a substantial hydrogen yield of 1.091 L g − 1 in methanol is retained. Furthermore, the desirable Zintl phase-water reaction inspires an economic-friendly “charge-hydrolysis-separation” strategy, for effectively recovering the valuable lithium, graphite, Si and Cu resources from the degraded lithium-ion batteries. Si-based hydrogen generation via hydrolysis/methanolysis faces reactivity challenges. Here, zintl-phase alkali–Si alloys, featuring discrete Si clusters with unpaired electrons, efficiently lower activation barriers, enabling high-yield, low-temperature H 2 release.

Highlights Hydrogen storage performance of V-Ti-based solid solution alloys is related to the elementary composition, phase structure, and homogeneity. Micro-strain accumulation is responsible for capacity degradation. Low-cost and high-performance V-Ti-based solid solution alloys with high reversible hydrogen storage capacity, good cyclic durability, and excellent activation performance should be developed. This review details the advancement in the development of V–Ti-based hydrogen storage materials for using in metal hydride (MH) tanks to supply hydrogen to fuel cells at relatively ambient temperatures and pressures. V–Ti-based solid solution alloys are excellent hydrogen storage materials among many metal hydrides due to their high reversible hydrogen storage capacity which is over 2 wt% at ambient temperature. The preparation methods, structure characteristics, improvement methods of hydrogen storage performance, and attenuation mechanism are systematically summarized and discussed. The relationships between hydrogen storage properties and alloy compositions as well as phase structures are discussed emphatically. For large-scale applications on MH tanks, it is necessary to develop low-cost and high-performance V–Ti-based solid solution alloys with high reversible hydrogen storage capacity, good cyclic durability, and excellent activation performance.

Highlights There is a novel “hydrolysis-driven synthesis” approach for the preparation of a dual-surface functionalized micron-sized Si anode with a SiO x /C layer. The functionalized inner pores and dual-functional SiO x /C layer synergistically alleviate volume change of Si lithiation, minimize stress concentration and improve electrochemical reaction kinetics. The optimized micron-Si anode performs impressive lifespan, excellent high rate capacity and outstanding stack cell volumetric energy density. Micro-silicon (Si) anode that features high theoretical capacity and fine tap density is ideal for energy-dense lithium-ion batteries. However, the substantial localized mechanical strain caused by the large volume expansion often results in electrode disintegration and capacity loss. Herein, a microporous Si anode with the SiO x /C layer functionalized all-surface and high tap density (~ 0.65 g cm⁻ 3 ) is developed by the hydrolysis-driven strategy that avoids the common use of corrosive etchants and toxic siloxane reagents. The functionalized inner pore with superior structural stability can effectively alleviate the volume change and enhance the electrolyte contact. Simultaneously, the outer particle surface forms a continuous network that prevents electrolyte parasitic decomposition, disperses the interface stress of Si matrix and facilitates electron/ion transport. As a result, the micron-sized Si anode shows only ~ 9.94 GPa average stress at full lithiation state and delivers an impressive capacity of 901.1 mAh g⁻ 1 after 500 cycles at 1 A g⁻ 1 . It also performs excellent rate performance of 1123.0 mAh g⁻ 1 at 5 A g⁻ 1 and 850.4 at 8 A g⁻ 1 , far exceeding most of reported literatures. Furthermore, when paired with a commercial LiNi 0.8 Co 0.1 Mn 0.1 O 2 , the pouch cell demonstrates high capacity and desirable cyclic performance.

Due to its relatively low cost, high hydrogen yield, and environmentally friendly hydrolysis byproducts, magnesium hydride (MgH2) appears to be an attractive candidate for hydrogen generation. However, the hydrolysis reaction of MgH2 is rapidly inhibited by the formation of a magnesium hydroxide passivation layer. To improve the hydrolysis properties of MgH2-based hydrides we investigated three different approaches: ball milling, synthesis of MgH2-based composites, and tuning of the solution composition. We demonstrate that the formation of a composite system, such as the MgH2/LaH3 composite, through ball milling and in situ synthesis, can improve the hydrolysis properties of MgH2 in pure water. Furthermore, the addition of Ni to the MgH2/LaH3 composite resulted in the synthesis of LaH3/MgH2/Ni composites. The LaH3/MgH2/Ni composites exhibited a higher hydrolysis rate—120 mL/(g·min) of H2 in the first 5 min—than the MgH2/LaH3 composite— 95 mL/(g·min)—without the formation of the magnesium hydroxide passivation layer. Moreover, the yield rate was controlled by manipulation of the particle size via ball milling. The hydrolysis of MgH2 was also improved by optimizing the solution. The MgH2 produced 1711.2 mL/g of H2 in 10 min at 298 K in the 27.1% ammonium chloride solution, and the hydrolytic conversion rate reached the value of 99.5%.

Metal atoms often locate in energetically favorite close-packed planes, leading to a relatively high penetration barrier for other atoms. Naturally, the penetration would be much easier through non-close-packed planes, i.e. high-index planes. Hydrogen penetration from surface to the bulk (or reversely) across the packed planes is the key step for hydrogen diffusion, thus influences significantly hydrogen sorption behaviors. In this paper, we report a successful synthesis of Mg films in preferential orientations with both close- and non-close-packed planes, i.e. (0001) and a mix of (0001) and (10 3), by controlling the magnetron sputtering conditions. Experimental investigations confirmed a remarkable decrease in the hydrogen absorption temperature in the Mg (10 3), down to 392 K from 592 K of the Mg film (0001), determined by the pressure-composition-isothermal (PCI) measurement. The ab initio calculations reveal that non-close-packed Mg(10 3) slab is advantageous for hydrogen sorption, attributing to the tilted close-packed-planes in the Mg(10 3) slab.

NaBH4 hydrolysis can generate pure hydrogen on demand at room temperature, but suffers from the difficult regeneration for practical application. In this work, we overview the state-of-the-art progress on the regeneration of NaBH4 from anhydrous or hydrated NaBO2 that is a byproduct of NaBH4 hydrolysis. The anhydrous NaBO2 can be regenerated effectively by MgH2, whereas the production of MgH2 from Mg requires high temperature to overcome the sluggish hydrogenation kinetics. Compared to that of anhydrous NaBO2, using the direct hydrolysis byproduct of hydrated NaBO2 as the starting material for regeneration exhibits significant advantages, i.e., omission of the high-temperature drying process to produce anhydrous NaBO2 and the water included can react with chemicals like Mg or Mg2Si to provide hydrogen. It is worth emphasizing that NaBH4 could be regenerated by an energy efficient method and a large-scale regeneration system may become possible in the near future.

Solid‐state hydrogen storage materials with optimal binding energy are essential for hydrogen storage and transportation applications and pose long‐standing challenges. Current technologies, including molecular physisorption materials (e.g., metal–organic frameworks (MOFs), carbon nanotubes (CNTs), activated carbons (ACs)) and atomic chemisorption materials (e.g., MgH2, LiBH4, NH4BH4), fall short of meeting practical application requirements. Therefore, designing and constructing new solid‐state hydrogen storage materials at the atomic level is critically important. In this study, the use of defect engineering is explored to modulate hydrogen adsorption sites on TiO2 surfaces. The results demonstrate that low‐coordinated titanium (Ti) atoms on TiO2 can serve as effective hydrogen adsorption sites, storing hydrogen through molecular chemisorption with significantly enhanced adsorption energy compared to Ti atoms in high coordination states. Moreover, the adsorbed hydrogen remains in molecular form, facilitating easy desorption at room temperature, unlike titanium hydride, which requires high temperatures for desorption. This approach provides a promising pathway for developing efficient hydrogen storage materials by leveraging the unique properties of low‐coordinated Ti atoms on TiO2 surfaces. This study investigates defect engineering on TiO₂ surfaces to enhance hydrogen storage. It demonstrates that low‐coordinated Ti atoms enable molecular chemisorption of H₂ with optimal binding energy, facilitating reversible adsorption at room temperature. This approach offers new perspectives for designing solid‐state hydrogen storage materials, providing innovative strategies to overcome current challenges.

Magnesium hydride (MgH2) exhibits great potential for hydrogen and lithium storage. In this work, MgH2-based composites with expanded graphite (EG) and TiO2 were prepared by a plasma-assisted milling process to improve the electrochemical performance of MgH2. The resulting MgH2–TiO2–EG composites showed a remarkable increase in the initial discharge capacity and cycling capacity compared with a pure MgH2 electrode and MgH2–EG composite electrodes with different preparation processes. A stable discharge capacity of 305.5 mAh·g−1 could be achieved after 100 cycles for the 20 h-milled MgH2–TiO2–EG-20 h composite electrode and the reversibility of the conversion reaction of MgH2 could be greatly enhanced. This improvement in cyclic performance is attributed mainly to the composite microstructure by the specific plasma-assisted milling process, and the additives TiO2 and graphite that could effectively ease the volume change during the de-/lithiation process as well as inhibit the particle agglomeration.

Fiber shaped supercapacitors are promising candidates for wearable electronics because they are flexible and light-weight. However, a critical challenge of the widespread application of these energy storage devices is their low cell voltages and low energy densities, resulting in limited run-time of the electronics. Here, we demonstrate a 1.5 V high cell voltage and high volumetric energy density asymmetric fiber supercapacitor in aqueous electrolyte. The lightweight (0.24 g cm −3 ), highly conductive (39 S cm −1 ) and mechanically robust (221 MPa) graphene fibers were firstly fabricated and then coated by NiCo 2 S 4 nanoparticles (GF/NiCo 2 S 4 ) via the solvothermal deposition method. The GF/NiCo 2 S 4 display high volumetric capacitance up to 388 F cm −3 at 2 mV s −1 in a three-electrode cell and 300 F cm −3 at 175.7 mA cm −3 (568 mF cm −2 at 0.5 mA cm −2 ) in a two-electrode cell. The electrochemical characterizations show 1000% higher capacitance of the GF/NiCo 2 S 4 as compared to that of neat graphene fibers. The fabricated device achieves high energy density up to 12.3 mWh cm −3 with a maximum power density of 1600 mW cm −3 , outperforming the thin-film lithium battery. Therefore, these supercapacitors are promising for the next generation flexible and wearable electronic devices.