A comprehensive review on unleashing the power of hydrogen: revolutionizing energy systems for a sustainable future

Population growth and environmental degradation are major concerns for sustainable development worldwide. Hydrogen is a clean and eco-friendly alternative to fossil fuels, with a heating value almost three times higher than other fossil fuels. It also has a clean production process, which helps to reduce the emission of hazardous pollutants and save the environment. Among the various production methodologies described in this review, biochemical production of hydrogen is considered more suitable as it uses waste organic matter instead of fossil fuels. This technology not only produces clean energy but also helps to manage waste more efficiently. However, the production of hydrogen obtained from this method is currently more expensive due to its early stage of development. Nevertheless, various research projects are underway to develop this method on a commercial scale.

Ultrasonic in-situ reduction preparation of SBA-15 loaded ultrafine RuCo alloy catalysts for efficient hydrogen storage of various LOHCs

SBA-15-loaded RuCo alloy nanoparticle catalysts (RuxCoy/S15-SU) for the efficient catalysis of hydrogen storage by various liquid organic hydrogen carriers (LOHCs) were prepared via strong electrostatic adsorption (SEA)-ultrasonic in-situ reduction (UR) technology. The above prepared catalysts were subjected to a series of characterization, such as XPS, H2-TPD/TPR, N2 adsorption-desorption, ICP, CO-chemisorption, FT-IR, XRD and TEM. Ru3+ and Co2+ were evenly anchored on the surface of SBA-15 by SEA, and ultrafine RuCo alloy nanoparticles were formed by UR without any chemical reducing or stabilizing agents. The addition of Co enhanced the dispersion and antioxidant capacity of the RuCo alloy NPs with an average particle size of 2.07 nm and increased the number of catalytically active sites. The synergistic effect of ultrafine particle size and electron transfer between Co and Ru improved the catalytic performance of monobenzyltoluene (MBT) for hydrogen storage. SEA-UR technology strengthened the coordination effect between RuCo alloy NPs and Si-OH, which enhanced the catalytic stability. H2-TPD and H2-TPR indicated that the addition of Co led to more activated H2 to produce hydrogen overflow. For the hydrogenation of MBT, the produced Ru2Co1/S15-SU showed excellent catalytic performance. The hydrogen storage efficiency of MBT was 99.98 % under 110 °C and 6 MPa H2 for 26 min, and the TOF was 145 min-1, which is significantly superior to that of Ru/S15-SU catalyst and that reported in the literature. The hydrogen storage efficiency was still as high as 99.7 % after ten cycles, which was much better than that of Ru/S15-SU and commercial 5 wt% Ru/Al2O3. Ru2Co1/S15-SU is also suitable for efficiently catalyzing hydrogen storage of N-ethylcarbazole, dibenzyltoluene and acenaphthene.

Unveiling the destabilization of sp3 and sp2 bonds in transition metal-modified borohydrides to improve reversible dehydrogenation and rehydrogenation

Borohydrides offer promise as potential carriers for hydrogen storage due to their high hydrogen concentration. However, the strong chemical bonding within borohydrides poses challenges for efficient hydrogen release during usage and restricts the re-hydrogenation process when attempting to regenerate the material. These high thermodynamic and kinetic barriers present obstacles in achieving reversible de-hydrogenation and re-hydrogenation of borohydrides, impeding their practical application in hydrogen storage systems. Employing density functional theory calculations, we conduct a comprehensive investigation into the influence of transition metals on both the BH4 cluster, a fundamental building block of borohydrides, and pure boron, which is formed as the end product following hydrogen release. Our research reveals correlations among the d-band center, work function, and surface energy of 3d and 4d transition metals. These correlations are directly linked to the weakening of bonding within the BH4 cluster when adsorbed on catalyst surfaces. On the other hand, we also explore how various intrinsic properties of transition metals influence the formation of boron vacancies and the hydrogen bonding process. By establishing a comprehensive correlation between the weakening of sp3 hybridization in the BH4 cluster and the sp2 hybridization in boron, we facilitate the identification and screening of optimal candidates capable of achieving reversible de-hydrogenation and re-hydrogenation in borohydrides.

Great Britain's power system with a high penetration of renewable energy: Dataset supporting future scenarios

The share of variable renewable energy (VRE) is forecasted to increase in the energy sector to meet decarbonization targets and/or reduce their dependence on fossil fuels. The modeling of future power system scenarios is crucial to assess the role of different flexibility options, including low-carbon technologies. The data presented here support the research article "The role of energy storage in Great Britain's future power system: focus on hydrogen and biomass". These data include updated parameters, inputs, equations, biomass resource potential and biomass demand to balance bio-power and bio-hydrogen requirements. The Future Renewable Energy Performance into the Power System Model (FEPPS), a rule-based model that includes flexibility and stability constraints, has been used, and the hourly results of future scenarios by 2030 and 2040 are provided. Researchers, policymakers, and investors could use this paper as these data provide insights into the role of different technologies (including hydrogen and biomass) in power generation, system flexibility, decarbonization and costs.

Boosting Hydrogen Storage Performance of MgH2 by Oxygen Vacancy-Rich H-V2O5 Nanosheet as an Excited H-Pump

MgH2 is a promising high-capacity solid-state hydrogen storage material, while its application is greatly hindered by the high desorption temperature and sluggish kinetics. Herein, intertwined 2D oxygen vacancy-rich V2O5 nanosheets (H-V2O5) are specifically designed and used as catalysts to improve the hydrogen storage properties of MgH2. The as-prepared MgH2-H-V2O5 composites exhibit low desorption temperatures (Tonset = 185 °C) with a hydrogen capacity of 6.54 wt%, fast kinetics (Ea = 84.55 ± 1.37 kJ mol-1 H2 for desorption), and long cycling stability. Impressively, hydrogen absorption can be achieved at a temperature as low as 30 °C with a capacity of 2.38 wt% within 60 min. Moreover, the composites maintain a capacity retention rate of ~ 99% after 100 cycles at 275 °C. Experimental studies and theoretical calculations demonstrate that the in-situ formed VH2/V catalysts, unique 2D structure of H-V2O5 nanosheets, and abundant oxygen vacancies positively contribute to the improved hydrogen sorption properties. Notably, the existence of oxygen vacancies plays a double role, which could not only directly accelerate the hydrogen ab/de-sorption rate of MgH2, but also indirectly affect the activity of the catalytic phase VH2/V, thereby further boosting the hydrogen storage performance of MgH2. This work highlights an oxygen vacancy excited "hydrogen pump" effect of VH2/V on the hydrogen sorption of Mg/MgH2. The strategy developed here may pave a new way toward the development of oxygen vacancy-rich transition metal oxides catalyzed hydride systems.

Exploring the structural, electronic, and hydrogen storage properties of hexagonal boron nitride and carbon nanotubes: insights from single-walled to doped double-walled configurations

This study investigates the structural intricacies and properties of single-walled nanotubes (SWNT) and double-walled nanotubes (DWNT) composed of hexagonal boron nitride (BN) and carbon (C). Doping with various atoms including light elements (B, N, O) and heavy metals (Fe, Co, Cu) is taken into account. The optimized configurations of SWNT and DWNT, along with dopant positions, are explored, with a focus on DWNT-BN-C. The stability analysis, employing binding energies, affirms the favorable formation of nanotube structures, with DWNT-C emerging as the most stable compound. Quantum stability assessments reveal significant intramolecular charge transfer in specific configurations. Electronic properties, including charge distribution, electronegativity, and electrical conductivity, are examined, showcasing the impact of doping. Energy gap values highlight the diverse electronic characteristics of the nanotubes. PDOS analysis provides insights into the contribution of atoms to molecular orbitals. UV-Vis absorption spectra unravel the optical transitions, showcasing the influence of nanotube size, dopant type, and location. Hydrogen storage capabilities are explored, with suitable adsorption energies indicating favorable hydrogen adsorption. The desorption temperatures for hydrogen release vary across configurations, with notable enhancements in specific doped DWNT-C variants, suggesting potential applications in high-temperature hydrogen release. Overall, this comprehensive investigation provides valuable insights into the structural, electronic, optical, and hydrogen storage properties of BN and C nanotubes, laying the foundation for tailored applications in electronics and energy storage.

A review on the research progress and application of compressed hydrogen in the marine hydrogen fuel cell power system

The urgency to mitigate greenhouse gas emissions from maritime vessels has intensified due to the increasingly stringent directives set forth by the International Maritime Organization (IMO). These directives specifically address energy efficiency enhancements and emissions reduction within the shipping industry. In this context, hydrogen is the much sought after fuel for all the global economies and its applications, for transportation and propulsion in particular, is crucial for cutting down carbon emissions. Nevertheless, the realization of hydrogen-powered vessels is confronted by substantial technical hurdles that necessitate thorough examination. This study undertakes a comprehensive analysis encompassing diverse facets, including distinct variations of hydrogen fuel cells, hydrogen internal combustion engines, safety protocols associated with energy storage, as well as the array of policies and commercialization endeavors undertaken globally for the advancement of hydrogen-propelled ships. By amalgamating insights from these multifaceted dimensions, this paper adeptly encapsulates the myriad challenges intrinsic to the evolution of hydrogen-fueled maritime vessels, while concurrently casting a forward-looking gaze on their prospective trajectory.

Hydrogen production and pollution mitigation: Enhanced gasification of plastic waste and biomass with machine learning & storage for a sustainable future

The pursuit of carbon neutrality confronts the twofold challenge of meeting energy demands and reducing pollution. This review article examines the potential of gasifying plastic waste and biomass as innovative, sustainable sources for hydrogen production, a critical element in achieving environmental reform. Addressing the problem of greenhouse gas emissions, the work highlights how the co-gasification of these feedstocks could contribute to environmental preservation by reducing waste and generating clean energy. Through an analysis of current technologies, the potential for machine learning to refine gasification for optimal hydrogen production is revealed. Additionally, hydrogen storage solutions are evaluated for their importance in creating a viable, sustainable energy infrastructure. The economic viability of these production methods is critically assessed, providing insights into both their cost-effectiveness and ecological benefits. Findings indicate that machine learning can significantly improve process efficiencies, thereby influencing the economic and environmental aspects of hydrogen production. Furthermore, the study presents the advancements in these technologies and their role in promoting a transition to a green economy and circular energy practices. Ultimately, the review delineates how integrating hydrogen production from unconventional feedstocks, bolstered by machine learning and advanced storage, can contribute to a sustainable and pollution-free future.

Enhanced hydrogen storage of alkaline earth metal-decorated Bn (n = 3-14) nanoclusters: a DFT study

CONTEXT

Boron-based nanostructures hold significant promise for revolutionizing hydrogen storage technologies due to their exceptional properties and potential in efficiently accommodating and interacting with hydrogen molecules. In this paper, boron-based Bn (n = 3-14) nanoclusters decorated with alkaline earth metals (AEM = Ca and Be) were investigated for hydrogen storage applications based on density function theory (DFT) calculations. To evaluate H2 adsorption capability, the adsorption energies, frontier molecular orbitals (FMOs), natural bond orbital (NBO), and quantum theory of atoms in molecule (QTAIM) analysis are performed. The primary aim of this research work is to achieve targeted value of 5.5 wt% set by the US Department of Energy (DOE) for the year 2025. The results revealed that B5Ca2, B6Ca2, and B10Ca2 structures have the ability to hold up to 12H2 molecules with gravimetric capacities of 15.20, 14.21, and 8.60 wt%, respectively, when compared to other boron structures decorated with calcium. Similarly, for Be-decorated structure, B3Be2 structure can accommodate 3H2 molecules with gravimetric capacity of 10.59 wt%. The result of this study indicates that AEM-decorated Bn nanoclusters hold great promise as potential materials for hydrogen storage.

METHODS

Density functional theory (DFT) approach at ωB97XD/6-311++G(d,p) level of theory is employed to investigate the possibility of storing H2 molecules on alkaline earth metal (AEM = Ca and Be)-decorated Bn (n = 3-14) nanoclusters. All DFT computations were performed using Gaussian 09 software. To calculate frontier molecular orbitals (FMOs) and quantum theory of atoms in molecule (QTAIM) analysis, we have used GaussView and Multiwfn software, respectively.

A data-guided approach for the evaluation of zeolites for hydrogen storage with the aid of molecular simulations

CONTEXT

This study employs a data-guided approach to evaluate zeolites for hydrogen storage, utilizing molecular simulations. The development of efficient and practical hydrogen storage materials is crucial for advancing clean energy technologies. Zeolites have shown promise as potential candidates due to their unique porous structure and tunable properties. However, the selection and design of suitable zeolites for hydrogen storage remain challenging. Therefore, this work aims to address this materials science question by utilizing molecular simulations and data-guided approaches to evaluate zeolites' performance for hydrogen storage. The results obtained from this study provide valuable insights into the evaluation of zeolites for hydrogen storage. Through molecular simulations, we analyze the adsorption behavior of hydrogen molecules in various zeolite structures. The performance of different zeolite frameworks in terms of hydrogen storage capacity, adsorption energy, and diffusion properties is assessed. Linde type A zeolite (LTA) had the highest capacity with a hydrogen capacity of 4.8wt% out of the 233 investigated zeolites. Furthermore, we investigate the influence of different factors such as mass (M), density (D), helium void fraction (HVF), accessible pore volume (APV), gravimetric surface area (GSA), and largest overall cavity diameter (Di) on the hydrogen storage performance of zeolites. The results show that Di, D, and M have a negative effect on the percentage weight capacity, while GSA and VSA have the highest positive contribution to the percentage weight. This study, therefore, provides new insights into the factors that affect their hydrogen storage capacity by exhibiting the importance of considering multiple factors when evaluating the performance of zeolites and demonstrates the potential of combining different computational methods to provide a more comprehensive understanding of materials. The current study contributes to the understanding of zeolite-based materials for hydrogen storage applications, aiding in the development of more efficient and practical hydrogen storage systems.

METHODS

Computational techniques were employed to investigate the hydrogen storage properties of zeolites. Molecular simulations were performed using classical force fields and molecular dynamics methods. The calculations were carried out at a force field level of theory with the GGA functional. To accurately capture the thermodynamics and kinetics of hydrogen adsorption, enhanced sampling techniques such as Monte Carlo simulations and molecular dynamics with metadynamics were utilized. We employed Grand Canonical Monte Carlo (GCMC) simulations to model hydrogen adsorption in zeolite structures for hydrogen storage. Our approach involved performing a substantial number of Monte Carlo steps (10,000) to ensure system equilibration and precise results. We defined a cutoff distance for particle interactions as 12.5 Ǻ and considered 0.000e framework charge per cell and 0.000e sorbate charge in energy calculations. The choice of an appropriate simulation cell size (50 × 50 × 50) Ǻ was crucial, mirroring real-world conditions. We specified lower and upper fugacity values (1 to 10 atm) to capture the range of gas pressures in the simulations. These methodical steps collectively enabled us to accurately model hydrogen adsorption within zeolites, forming the core of our hydrogen storage evaluation. In this research, we utilized DFT calculations to thoroughly investigate the interactions between zeolites and hydrogen. We employed pseudopotentials to describe electron behavior in zeolite systems, choosing them in line with DFT norms and basis set compatibility. Our simulation cell design replicated zeolite periodicity and eliminated boundary effects. Pre-geometry optimization was performed with HyperChem29, ensuring stable conformations with strict convergence criteria. We utilized 6-31 + G(d) and LanL2DZ basis sets for light and heavy atoms, aligning with field standards for computational efficiency and precision. A machine learning algorithm was used to rank the importance of various structural features such as mass (M), density (D), helium void fraction (HVF), accessible pore volume (APV), gravimetric surface area (GSA), and largest overall cavity diameter (Di) and how they affect the capacity of the zeolites. Machine learning analysis was performed with the Scikit-learn library, an open-source Python tool. We employed a range of machine learning models, including SVMs, random forests, and neural networks, primarily for data analysis and feature extraction. Pearson correlation analysis, a classical statistical technique, was used to evaluate linear relationships between variables and assess the strength and direction of these relationships. It served as a complementary tool to understand the interplay of variables in our dataset, distinguishing it from machine learning algorithms. Further quantum chemical calculations were also performed to calculate the adsorption energy, global reactivity electronic descriptors, and natural bond orbital analysis in order to provide insights into the interaction of the zeolites with hydrogen. The simulations and data analysis were performed using BIOVIA material studio software, Gaussian, and Origin Pro software.

Nanomaterials: paving the way for the hydrogen energy frontier

This comprehensive review explores the transformative role of nanomaterials in advancing the frontier of hydrogen energy, specifically in the realms of storage, production, and transport. Focusing on key nanomaterials like metallic nanoparticles, metal-organic frameworks, carbon nanotubes, and graphene, the article delves into their unique properties. It scrutinizes the application of nanomaterials in hydrogen storage, elucidating both challenges and advantages. The review meticulously evaluates diverse strategies employed to overcome limitations in traditional storage methods and highlights recent breakthroughs in nanomaterial-centric hydrogen storage. Additionally, the article investigates the utilization of nanomaterials to enhance hydrogen production, emphasizing their role as efficient nanocatalysts in boosting hydrogen fuel cell efficiency. It provides a comprehensive overview of various nanocatalysts and their potential applications in fuel cells. The exploration extends to the realm of hydrogen transport and delivery, specifically in storage tanks and pipelines, offering insights into the nanomaterials investigated for this purpose and recent advancements in the field. In conclusion, the review underscores the immense potential of nanomaterials in propelling the hydrogen energy frontier. It emphasizes the imperative for continued research aimed at optimizing the properties and performance of existing nanomaterials while advocating for the development of novel nanomaterials with superior attributes for hydrogen storage, production, and transport. This article serves as a roadmap, shedding light on the pivotal role nanomaterials can play in advancing the development of clean and sustainable hydrogen energy technologies.

Effect of Zr3Fe addition on hydrogen storage behaviour of Ti2CrV alloys

In this work, the hydrogen storage behavior of Ti2CrV + X wt.% Zr3Fe, where X = 2, 4, 6, 8 and 10 was investigated. The synthesis of all samples was carried out through arc-melting, followed by comprehensive characterization using X-ray diffraction, scanning electron microscopy, and energy-dispersive spectroscopy. The pure-Ti2CrV as-cast sample presented a single-phase microstructure. However, the addition of the Zr3Fe led to a remarkable transformation, resulting in the appearance of a Zr-rich secondary phase. It was found that the first hydrogenation is improved with the addition of at least 6 wt% of Zr3Fe, avoiding any preheating of the sample. These samples achieved their maximum capacity in approximately 10 min at room temperature. The maximum capacity recorded was 4.2 wt% H for the sample with X = 6 wt% Zr3Fe, while for X = 8 and 10 wt% Zr3Fe, the capacity recorded was 4.1 wt% and 4.0 wt%, respectively.

Ab initio insight into the physical properties of MgXH3 (X = Co, Cu, Ni) lead-free perovskite for hydrogen storage application

Renewable energy systems are vital for a sustainable future, where solid-state hydrogen storage can play a crucial role. Perovskite hydride materials have attracted the scientific community for hydrogen storage applications. The current work focuses on the theoretical study using density functional theory (DFT) to evaluate the characteristics of MgXH3 (X = Co, Cu, Ni) hydrides. The structural, vibrational, electronic, mechanical, thermodynamic, and hydrogen storage properties of these hydrides were investigated. The equilibrium lattice parameters were calculated using the Birch-Murnaghan equation of state-to-energy volume curves. The elastic constants (Cij) and relevant parameters, such as Born criteria, were calculated to confirm the mechanical stability of the hydrides. The Cauchy pressure (Cp) revealed brittle or ductile behavior. The outcomes of the Pugh ratio, Poisson ratio, and anisotropy were also calculated and discussed. The absence of negative lattice vibrational frequencies in phonon dispersion confirmed the lattice's dynamic stability. The heat capacity curves of thermodynamic properties revealed that hydrides can conduct thermal energy. The metallic character and ample interatomic distances of hydrides were confirmed by the band structure and population analysis, which confirmed that hydrides can conduct electrical energy and adsorb hydrogen. The density of state (DOS) and partial DOS unveiled the role of specific atoms in the DOS of the crystal. The calculated gravimetric hydrogen storage capacity of MgCoH3, MgCuH3, and MgNiH3 hydrides was 3.64, 3.32, and 3.49wt%, respectively. Our results provide a deeper understanding of its potential for hydrogen storage applications through a detailed analysis of MgXH3 (X = Co, Cu, Ni) perovskite hydride material.

A graphene-based material for green sustainable energy technology for hydrogen storage

The usage of graphene-based materials (GMs) as energy storage is incredibly popular. Significant obstacles now exist in the way of the generation, storage and consumption of sustainable energy. A primary focus in the work being done to advance environmentally friendly energy technology is the development of effective energy storage materials. Due to their distinct two-dimensional structure and intrinsic physical qualities like good electrical conductivity and wide area, graphene-based materials have a significant potential to be used in energy storage devices. Graphene and GMs have been employed extensively for this due to their special mechanical, thermal, catalytic and other functional qualities. In this review, we covered the topic of employing GMs to store hydrogen for green energy.

Scheduling optimization of wind-thermal interconnected low-carbon power system integrated with hydrogen storage

To improve the consumption of wind energy and reduce carbon emission, this paper proposes a wind-thermal interconnected low-carbon power system integrated with hydrogen storage. An energy scheduling optimization model aiming at minimizing the daily operation cost of the system is constructed considering environmental operation cost quantification, and whale optimization algorithm is used to optimize multiple variables. Finally, in simulation example, various scenarios are set considering the application way of hydrogen and the scenarios with and without the carbon capture and storage (CCS) are optimized, respectively. The horizontal comparison results show that the system with hydrogen production (S2) and the system with hydrogen fuel cell (S3) have higher economic operation cost than that of wind-thermal interconnected power system only (S1), but the environmental cost is reduced; the system's daily operating costs are reduced. The wind curtailment rate decreases from 11.0% (S1) to 3.8% (S2 and S3) without CCS, and from 9.0% (S1) to 2.1% (S2 and S3) with CCS. The longitudinal comparison shows that the thermal power output is reduced and the wind power consumption is improved with CCS. The addition of CCS increases total operating costs but significantly reduces environmental costs. Configuring hydrogen storage system in the wind-thermal interconnected power system can effectively promote the consumption of wind energy and reduce the system operation cost; however, the utilization of CCS is economic unfriendly at present.

A study of the magnetic properties of LaNi5 and their effect on hydrogen desorption under theaction of a magnetostatic field

A study of the magnetic properties of LaNi5 intermetallic compoundand and their effect on desorption reaction was carried out as a function of temperature. A Vibrating Sample Magnetometer (VSM) was used for the magnetic measurements and a Metal Hydrogen Reactor (MHR) supplied by a constant current through a coil was used for the hydrogen desorption reaction under the action of a magnetostatic field. Then, the hysteresis cycle, the first magnetization curve, the thermo-magnetization curves and the desorbed hydrogen mass were determined. The results showed that the application of a magnetic field corresponding to the magnetization at saturation Ms at a given temperature improved the hydrogen desorption reaction by the LaNi5.

Synthesis, characterization, and electrochemical evaluation of SnFe2O4@MWCNTS nanocomposite as a potential hydrogen storage material

The widespread use of hydrogen as a vehicle fuel has prompted us to develop a new nanocomposite by immobilizing of tin ferrite nanoparticles (SnFe₂O₄) on the surface of multi-walled carbon nanotubes (abbreviated as MWCNT_S) for the first time. The prepared nanocomposite powder (SnFe₂O₄@MWCNT_S) was investigated utilizing various microscopy and spectroscopy methods, such as FT-IR, XRD, SEM, EDX, and BET techniques. Moreover, the electrochemical property of SnFe₂O₄@MWCNT_S nanocomposite was investigated by cyclic voltammogram (CV) and charge-discharge chronopotentiometry (CHP) techniques. A variety of factors on the hydrogen storage capacity, such as current density, surface area of the copper foam, and the influence of repeated hydrogen adsorption-desorption cycles were assessed. The electrochemical results indicated that the SnFe₂O₄@MWCNT_S has high capability and excellent reversibility compared to SnFe₂O₄ nanoparticles (NPs) for hydrogen storage. The highest hydrogen discharge capability of SnFe₂O₄@MWCNTs was achieved ∼ 365 mAh/g during the 1st cycle, and the storage capacity enhanced to ∼ 2350 mAh/g at the end of 20 cycles using a current of 2 mA. Consequently, the SnFe₂O₄@MWCNT_S illustrated great capacity as a prospective active material for hydrogen storage systems.

Experimental study of the microstructures and hydrogen storage properties of the LaNi4Mn0·5Co0.5 alloys

In the present study, the absorption and desorption kinetics of hydrogen and the isotherm (P-C-T)) of the LaNi₄Mn_0·5Co_0.5 alloy were measured at values of 283 K, 303 K, and 313 K. The morphological states of this sample were examined using characterization techniques, including X-ray diffraction and scanning electron microscopy. The thermodynamic functions for the absorption-desorption of hydrogen by hydrides, such as enthalpy (H) and entropy (S), were calculated from the experimental data or by using a model that exists in the literature and is premised on the adjustment of isotherm curves at various temperatures. This model is based on an integrated form of the Van't Hoff equation and a simultaneous examination of the isotherms. According to the experimental results, the amount of hydrogen absorbed or desorbed by the sample is significantly affected by the partial substitution of the nickel atom by the elements Mn and Co. However, this substitution increased the absorption or de-sorption plateau pressure.

The effect of strain on hydrogen storage characteristics in K2NaAlH6 double perovskite hydride through first principle method

Today, hydrogen is one of the most credible options for a non-polluting, carbon-free energy carrier. Hydrogen can be obtained or produced by different means from different renewable energy sources and can be stored in solid, liquid, or gaseous form. Storing hydrogen in complex hydrides in solid form is one of the most efficient methods of storage because they are secure, offer high hydrogen capacity, and demand optimal functioning conditions. Complex hydrides give a large gravimetric capacity that allows large amounts of hydrogen to be stored. This study examined the effects of triaxial strains on hydrogen storage properties of the perovskite-type compound K₂NaAlH₆. The analysis was conducted through first principle calculations using the full potential linearized augmented plane wave (FP-LAPW) approach. Our results indicate that the formation energy and desorption temperature of K₂NaAlH₆ hydride were improved under a maximum triaxial compressive strains of ε ≈ - 5%. Specifically, the values of formation energy and desorption temperature were - 40.14 kJ/mol.H₂ and 308.72 K, respectively, compared to the original values of - 62.98 kJ/mol.H₂ and 484.52 K. In addition, the analysis of the densities of states showed that changes in the dehydrogenation and structural properties of K₂NaAlH₆ were closely linked to the Fermi level value of the total densities of states. These findings provide valuable insights into the potential of K₂NaAlH₆ as a hydrogen storage material.

Enhanced dehydrogenation properties of MgH2 by the synergetic effects of transition metal carbides and graphene

Transition metal carbides show remarkable catalysis for MgH2, and the addition of carbon materials can attach excellent cycling stability. In this paper, Mg-doped with transition metal carbides (TiC) and graphene (G) composite (denoted as Mg-TiC-G) is designed to assess the influence of TiC and graphene on the hydrogen storage performance of MgH2. The as-prepared Mg-TiC-G samples showed favorable dehydrogenation kinetics compared to the pristine Mg system. After adding TiC and graphene, the dehydrogenation activation energy of MgH2 decreases from 128.4 kJ∙mol-1 to 111.2 kJ∙mol-1. The peak desorption temperature of MgH2 doped with TiC and graphene is 326.5 ℃, which is 26.3 ℃ lower than the pure Mg. The improved dehydrogenation performance of Mg-TiC-G composites is attributed to synergistic effects between catalysis and confinement.&#xD.

Enhanced hydrogen storage performance of Li and Co functionalized h-GaN nanosheets: DFT study

Based on the density functional theory (DFT) computations, we investigated the hydrogen storage performances of alkali metal (Li) and transition metal (Co) decorated the defective GaN nanosheets. Fundamental aspects including the interaction properties, bonding characteristics, adsorption ability, frontier orbital, HOMO-LUMO energy gaps, natural bond orbital (NBO) analysis, projected densities of states (PDOS) and statistical thermodynamic stability have been demonstrated to analyze the interaction properties of H₂ molecules. As a theoretical strategy, non-covalent interactions (NCI) and the atoms in molecules (QTAIM) descriptors were performed to depict weak interactions. The Li_N-GaN and Co_N-GaN systems and the H₂ uptake capacity revealed to be 7.78% and 5.55%, respectively. Our results demonstrated that H₂ molecules are introduced sequentially on the Li and Co that functionalized both sides of V_N-GaN nanosheets yielded the gravimetric densities up to 8.158% (2Co-V_N-GaN) that well above the gravimetric DOE achieve. The 2Li_N-GaN and 2Co_N-GaN are energetically more effective for the H₂ adsorption, stable and preferred than pristine GaN nanosheet. Additionally, two binding mechanisms including polarization of the hydrogen molecules and σ orbitals hybridization of H₂ molecules have been investigated to explain the interaction of H₂ molecules. The hydrogen desorption enthalpy and desorption temperatures of hydrogen molecules, indicating the H₂ molecules are easy to desorb from Li and Co decorated defective GaN nanosheets. These results suggest the possibility of an excellent and promising nanostructural material to improve the performance of hydrogen storage for in fuel cells application at ambient temperature.

Hydrogen adsorption on lithium clusters coordinated to a gC3N4 cavity

The search of new materials having suitable characteristics to trap hydrogen for fuel applications is greatly challenging due to the stringent requirements that such materials must meet. In this sense, with the aid of computational chemistry, significant advances can be achieved. The present work explores the adsorption of hydrogen molecules by lithium clusters (Li_n, where n = 1-6) coordinated to a graphitic carbon nitride (heptazine, gC₃N₄) cavity. The study was conducted using the density functional theory (M06-2X-D3) in combination with the def2-TZVP basis set. Our results suggest that lithium atoms in the gC₃N₄-cavity can coordinate up to 10 hydrogen molecules with bond energies in the range -0.10 to -0.19 eV. The [gC₃N₄Li₅]⁺ and [gC₃N₄Li₆] systems resulted to be the most promising in terms of lithium coordination. They feature the highest stabilization energies for hydrogen adsorption. According to the calculated Gibbs free energies for these systems, H₂ adsorption remains a spontaneous process even at 400 K.

Nanostructuring of Mg-Based Hydrogen Storage Materials: Recent Advances for Promoting Key Applications

A comprehensive discussion of the recent advances in the nanostructure engineering of Mg-based hydrogen storage materials is presented. The fundamental theories of hydrogen storage in nanostructured Mg-based hydrogen storage materials and their practical applications are reviewed. The challenges and recommendations of current nanostructured hydrogen storage materials are pointed out.

Abstract

With the depletion of fossil fuels and global warming, there is an urgent demand to seek green, low-cost, and high-efficiency energy resources. Hydrogen has been considered as a potential candidate to replace fossil fuels, due to its high gravimetric energy density (142 MJ kg−1), high abundance (H2O), and environmental-friendliness. However, due to its low volume density, effective and safe hydrogen storage techniques are now becoming the bottleneck for the "hydrogen economy". Under such a circumstance, Mg-based hydrogen storage materials garnered tremendous interests due to their high hydrogen storage capacity (~ 7.6 wt% for MgH2), low cost, and excellent reversibility. However, the high thermodynamic stability (ΔH =  − 74.7 kJ mol−1 H2) and sluggish kinetics result in a relatively high desorption temperature (> 300 °C), which severely restricts widespread applications of MgH2. Nano-structuring has been proven to be an effective strategy that can simultaneously enhance the ab/de-sorption thermodynamic and kinetic properties of MgH2, possibly meeting the demand for rapid hydrogen desorption, economic viability, and effective thermal management in practical applications. Herein, the fundamental theories, recent advances, and practical applications of the nanostructured Mg-based hydrogen storage materials are discussed. The synthetic strategies are classified into four categories: free-standing nano-sized Mg/MgH2 through electrochemical/vapor-transport/ultrasonic methods, nanostructured Mg-based composites via mechanical milling methods, construction of core-shell nano-structured Mg-based composites by chemical reduction approaches, and multi-dimensional nano-sized Mg-based heterostructure by nanoconfinement strategy. Through applying these strategies, near room temperature ab/de-sorption (< 100 °C) with considerable high capacity (> 6 wt%) has been achieved in nano Mg/MgH2 systems. Some perspectives on the future research and development of nanostructured hydrogen storage materials are also provided.

Graphical Abstract

Investigation of unified impact of Ti adatom and N doping on hydrogen gas adsorption capabilities of defected graphene sheets

In this work, we studied the hydrogen adsorption capabilities of functionalized graphene sheets containing a variety of defects (D-G) via molecular dynamics (MD) simulations that govern the mechanisms involved in hydrogen adsorption. Specifically, the graphene sheets containing monovacancy (MV), Stone-Wales (SW), and multiple double vacancy (DV) defects were functionalized with Ti and N atoms to enhance their hydrogen adsorption capacity. We measured the adsorption capacities of the N-/D-G sheets with varying concentrations of Ti adatoms at 300 K and 77 K temperatures and various pressures. Our study revealed that the increasing concentration of Ti adatoms on the D-G sheets led to a significant improvement in the hydrogen adsorption capacity of the graphene sheets. The DV(III)-G sheets showed the maximum adsorption capacity at 300 K because the DV(III)-G sheets had a small number of large-sized pores that bind hydrogen with high binding energy. Thus, hydrogen remained adsorbed even at higher temperatures (300 K). The N doping on the D-G sheets initially reduced their hydrogen adsorption capabilities; however, the N-D-G sheets enhanced their hydrogen adsorption capacity with the increasing concentrations of Ti adatoms. Compared to all other defect types, the Ti-N-DV(III)-G sheet with a Ti concentration of 10.5% showed a hydrogen uptake of 5.5 wt% at 300 K and 100 bar pressure. Thus, the N doping and Ti implantations improved the hydrogen storage capabilities of the graphene sheets, and these findings helped design solid-state hydrogen storage systems operating at ambient conditions and moderate pressure ranges.

First-principles calculations of Mg2FeH6 under high pressures and hydrogen storage properties

We report on structural properties, elastic constants, mechanical and dynamical stabilities, electronic band structure, and hydrogen storage applications of Mg2FeH6 at zero and high-pressure effects. The work has been realized within the full-potential linearized augmented plane wave method. At zero pressure, the material under study is stable and has a ductile nature. The electronic structure of the material of interest is determined to be X-X wide direct band gap semiconductor with an energy of 1.88 eV. The hydrogen storage capacity wt (%) and the hydrogen desorption temperature are reported as 5.473 and 625.47 K respectively. The Debye temperature ϴD is recorded as 698 K using the elastic constants and about 775 K using the Gibbs calculations. Under high-pressure effect up to 80 GPa, the semiconductor still be an X-X semiconductor with an energy gap of 3.91 eV. The Debye temperature ϴD increases monotonically up to about 1120 K at 80 GPa when using the calculated elastic constants whereas the desorption temperature decreases from 650 to 0 K by increasing pressure from 0 to about 87 GPa.

Gd(III) metal-organic framework as an effective humidity sensor and its hydrogen adsorption properties

Metal-organic frameworks (MOFs) represent a class of nanoporous materials built up by metal ions and organic linkers with several interesting potential applications. The present study described the synthesis and characterization of Gd(III)-based MOF with the chemical composition [Gd(BTC)(H₂O)]·DMF (BTC - trimesate, DMF = N,N'-dimethylformamide), known as MOF-76(Gd) for hydrogen adsorption/desorption capacity and humidity sensing applications. The structure and morphology of as-synthesized material were studied using powder X-ray diffraction, scanning and transmission electron microscopy. The crystal structure of MOF-76(Gd) consists of gadolinium (III) and benzene-1,3,5-tricarboxylate ions, one coordinated aqua ligand and one crystallization DMF molecule. The polymeric framework of MOF-76(Gd) contains 1D sinusoidally shaped channels with sizes of 6.7 × 6.7 Å propagating along c crystallographic axis. The thermogravimetric analysis, heating infrared spectroscopy and in-situ heating powder X-ray diffraction experiments of the prepared framework exhibited thermal stability up to 550 °C. Nitrogen adsorption/desorption measurement at -196 °C showed a BET surface area of 605 m² g^-1 and pore volume of 0.24 cm³ g^-1. The maximal hydrogen storage capacity of MOF-76(Gd) was 1.66 wt % and 1.34 wt % -196 °C and -186 °C and pressure up to 1 bar, respectively. Finally, the humidity sensing measurements (water adsorption experiments) were performed, and the results indicate that MOF-76(Gd) is a suitable material for moisture sensing application with a fast response (11 s) and recovery time (2 s) in the relative humidity range of 11-98%.

Oxygen Vacancy-Rich 2D TiO2 Nanosheets: A Bridge Toward High Stability and Rapid Hydrogen Storage Kinetics of Nano-Confined MgH2

MgH₂ has attracted intensive interests as one of the most promising hydrogen storage materials. Nevertheless, the high desorption temperature, sluggish kinetics, and rapid capacity decay hamper its commercial application. Herein, 2D TiO₂ nanosheets with abundant oxygen vacancies are used to fabricate a flower-like MgH₂/TiO₂ heterostructure with enhanced hydrogen storage performances. Particularly, the onset hydrogen desorption temperature of the MgH₂/TiO₂ heterostructure is lowered down to 180 °C (295 °C for blank MgH₂). The initial desorption rate of MgH₂/TiO₂ reaches 2.116 wt% min^-1 at 300 °C, 35 times of the blank MgH₂ under the same conditions. Moreover, the capacity retention is as high as 98.5% after 100 cycles at 300 °C, remarkably higher than those of the previously reported MgH₂-TiO₂ composites. Both in situ HRTEM observations and ex situ XPS analyses confirm that the synergistic effects from multi-valance of Ti species, accelerated electron transportation caused by oxygen vacancies, formation of catalytic Mg-Ti oxides, and stabilized MgH₂ NPs confined by TiO₂ nanosheets contribute to the high stability and kinetically accelerated hydrogen storage performances of the composite. The strategy of using 2D substrates with abundant defects to support nano-sized energy storage materials to build heterostructure is therefore promising for the design of high-performance energy materials.

Reinforcing the tetracene-based two-dimensional C48H16 sheet by decorating the Li, Na, and K atoms for hydrogen storage and environmental application -A DFT study

To meet the increasing need of energy resources, hydrogen (H₂) is being considered as a promising candidate for energy carrier that has motivated research into appropriate storage materials among scientists. Thus, in this study for the first time, zig-zag and armchair edged tetracene based porous carbon sheet (C₄₈H₁₆) is investigated for H₂ storage using the density functional theory. To explore the hydrogen storage capacity, the hydrogen molecule is initially positioned parallel to the C₄₈H₁₆ sheet at three different sites, resulting in lower adsorption energies of -0.020, -0.024, and -0.015 eV respectively. The Li, Na, and K atoms are decorated to improve H₂ adsorption on the C₄₈H₁₆ sheet. The Li atom decorated C₄₈H₁₆ sheet has a higher binding energy value of -2.070 eV than the Na and K atom decorated C₄₈H₁₆ sheet. The presence of Li, Na, and K atoms on the C₄₈H₁₆ sheet enhance the H₂ adsorption energy than the H₂ on the pristine C₄₈H₁₆ sheet. The decrease of Mulliken charge in alkali metal atoms (Li, Na, and K atom) on the C₄₈H₁₆ sheet reveal that the electron is transferred from H-σ orbital to s orbital of alkali metal atoms on the C₄₈H₁₆ sheet, leads to the enhancement of H₂ binding. Compared to H₂ adsorption on Na and K atom decorated C₄₈H₁₆ sheet, the H₂ adsorption on Li atom decorated C₄₈H₁₆ sheet has the maximum adsorption energy value of -0.389 eV. The obtained hydrogen storage capacity of Li, Na, and K atoms decorated C₄₈H₁₆ sheets are about 7.49 wt%, 7.31 wt%, and 7.14 wt% respectively for four H₂ molecules, which is greater than the targeted hydrogen storage capacity of the United States Department of Energy (DOE). Thus the obtained results in this work reveal that the decorated C₄₈H₁₆ sheets with Li, Na, and K atom plays the potential role in the H₂ storage.

Density functional theory studies on C20 with substitutional TinNn impurities

In this paper, we have performed systematic theoretical surveys of C₂₀ and its C_20-2nTi_nN_n nanocages with n = 1-8 at DFT. Full optimization indicates none of the structures collapse to open deformed as segregated heterofullerene. Also, in order to avoid the resulted strain of fused five-pentagon configuration, some of them deform their cage at the Ti-N bonds and appear cubic-like. Binding energy (E_b) increases, and the absolute heat of atomization │ΔH_at│ of the designed C_20-2nTi_nN_n structures decreases, respectively, as the number of substituting Ti-N units increases. The calculated E_b of 57.05 eV/atom and │ΔH_at│ of 2437.40 kcal/mol display C₄Ti₈N₈ as the most thermodynamic stable heterofullerene where including eight separated Ti-N units through two double C═C bonds. In contrast, the calculated band gap of 2.06 eV shows C₁₈Ti₁N₁ as the best-insulated heterofullerene. Here isolable or extractable open-shell C₁₈Ti₁N₁ heterofullerene must be kinetic stable species, and closed-shell C₄Ti₈N₈ should be thermodynamic stable species. Compared to the suggested Ti-decorated B₃₈ fullerene as a high capacity hydrogen storage material with large E_b (5.67 eV/atom), our studied C_20-2nTi_nN_n heterofullerenes show the higher E_b with a range of 13.78 to 57.05 eV/atom, the higher stability, and the higher capacity hydrogen storage. Each Ti-N unit can bind up to two hydrogen molecules with an average adsorption energy of 0.073 eV/H₂. While the C₄Ti₈N₈ fullerene substituted with 8 Ti-N units can store 16 H₂ molecules, the hydrogen gravimetric density (the hydrogen storage capacity) reaches up to 5.61 wt% with an average adsorption energy of 0.587 eV/H₂. Based on these results, we infer that C₄Ti₈N₈ fullerene is a potential material for hydrogen storage with high capacity and might motivate active experimental efforts in designing hydrogen storage media.

High-Entropy Alloys for Solid Hydrogen Storage: Potentials and Prospects

Hydrogen storage is one of the most significant research areas for exploiting hydrogen energy economy. To store hydrogen with a high gravimetric/volumetric density, gaseous hydrogen storage systems require a very high-pressure compressed gas cylinder which is quite unsafe and the storage in the liquid form needs cryogenic containers to be maintained at roughly 20 K under ambient pressure because hydrogen has a very low critical temperature of 33 K. However, hydrogen can be stored in solid materials with higher concentration of hydrogen compared to the gaseous and liquid hydrogen storage systems. It is therefore, worthwhile to look into the experimental and theoretical research on prospective hydrogen storage materials. The hydride-forming alloys and intermetallic compounds are found to be the most important families of hydrogen storage materials. Multicomponent alloys consisting of five or more principal elements, also known as high-entropy alloys appear to have potential for the development as hydrogen storage materials. Hydride-forming elements like Ti, Zr, V, Nb, Hf, Ta, La, Ce, Ni, and others have been shown to have hydrogen storage properties and the ability to produce single-phase high-entropy intermetallics. Here, attempts will be made to present a short review on utilization of multicomponent high-entropy alloys as solid hydrogen storage materials. Furthermore, we will also present some of our work on the synthesis, structural-microstructural characterization and hydrogen storage properties of Ti-Zr-V-Cr-Ni equi-atomic hydride-forming high-entropy alloys. From the preliminary investigation, the maximum storage capacity in this system was observed to be 1.78 wt%, which is comparable to other hydrogen storage materials. The prospects of high-entropy-based alloys for hydrogen storage will be discussed.

Hydrogen storage in purified multi-walled carbon nanotubes: gas hydrogenation cycles effect on the adsorption kinetics and their performance

Multi-walled carbon nanotubes (MWCNTs) are an alternative for storage with low cost, eco-friendly, and good performance for both process adsorption and desorption. Herein, a purification procedure of MWCNTs was successfully described and studied by using XRD, TEM, Raman spectroscopy and by means of N₂ adsorption-desorption isotherms using the BET method. The H₂ storage properties at room temperature of the purified carbon nanotubes exposed to gas under pressures between 0.39 and 13.33 kPa was investigated by using the quartz crystal microbalance technique. It was found that the H₂ adsorption capacity is strongly dependent on the morphological and structural characteristics of the carbon nanotubes and their specific surface area. The best sample with specific surface area of 729.4 ± 3 m² g⁻¹ shows a maximum adsorption capacity of 3.46 wt% at 12.79 kPa of H₂ exposure pressure. The adsorption kinetics (t_95%) from the different purified MWCNTs was also investigated as a function of the H₂ exposure pressure as well as the performance of these MWCNTs on the reversibility of the H₂ loading/unloading process when underwent to successive cycles of gas exposure.

Ultrasound-excited hydrogen radical from NiFe layered double hydroxide for preparation of ultrafine supported Ru nanocatalysts in hydrogen storage of N-ethylcarbazole

Highly active Ru nanoparticles (Ru NPs) supported on NiFe layered double hydroxide (Ru/NiFe-LDH) are prepared easily using ultrasound-assisted reduction method without chemical reductants and stabilizers. The plentiful hydroxyls on NiFe-LDH are excited into hydrogen radicals (H) under the action of ultrasound for reducing Ru3+ to Ru0. Ru NPs with an average particle size of 1.26 nm highly disperse on the mesopore-like surface of NiFe-LDH, which improve the catalytic performance for N-ethylcarbazole (NEC) hydrogenation. The experimental results show that 5Ru/NiFe-LDH-300-60 exhibits the best catalytic performance with 100% conversion of NEC, 98.88% yield of dodecahydro-N-ethylcarbazole (12H-NEC) and 5.77 wt% mass hydrogen storage capacity under the reaction conditions of 110 ℃, 6 MPa and mRu:mNEC = 0.15 wt% for 80 min. The kinetics study shows that the apparent activation energy is only 25.15 kJ/mol, which is the lowest in the reported literatures. Ru complexes with O-contained groups on NiFe-LDH, improving the catalytic stability in NEC hydrogenation.

Atomic Clusters: Structure, Reactivity, Bonding, and Dynamics

Atomic clusters lie somewhere in between isolated atoms and extended solids with distinctly different reactivity patterns. They are known to be useful as catalysts facilitating several reactions of industrial importance. Various machine learning based techniques have been adopted in generating their global minimum energy structures. Bond-stretch isomerism, aromatic stabilization, Rener-Teller effect, improved superhalogen/superalkali properties, and electride characteristics are some of the hallmarks of these clusters. Different all-metal and nonmetal clusters exhibit a variety of aromatic characteristics. Some of these clusters are dynamically stable as exemplified through their fluxional behavior. Several of these cluster cavitands are found to be agents for effective confinement. The confined media cause drastic changes in bonding, reactivity, and other properties, for example, bonding between two noble gas atoms, and remarkable acceleration in the rate of a chemical reaction under confinement. They have potential to be good hydrogen storage materials and also to activate small molecules for various purposes. Many atomic clusters show exceptional opto-electronic, magnetic, and nonlinear optical properties. In this Review article, we intend to highlight all these aspects.

Hydrogen fuel and fuel cell technology for cleaner future: a review

One of the main problems facing our planetary bodies is unexpected and sudden climate change due to continuously increasing global energy demand, which currently is being met by fossil fuels. Hydrogen is considered as one of the major energy solutions of the twenty-first century, capable of meeting future energy needs. Being 61a zero-emission fuel, it could reduce environmental impacts and craft novel energy opportunities. Hydrogen through fuel cells can be used in transport and distributed heating, as well as in energy storage systems. The transition from fossil-based fuels to hydrogen requires intensive research to overcome scientific and socio-economic barriers. The purpose of this paper is to reflect the current state, related issues, and projection of hydrogen and fuel elements within the conceptual framework of 61a future sustainable energy vision. An attempt has been made to compile in this paper the past hydrogen-related technologies, present challenges, and role of hydrogen in the future.

Hydrogen fuel and fuel cell technology for cleaner future: a review

One of the main problems facing our planetary bodies is unexpected and sudden climate change due to continuously increasing global energy demand, which currently is being met by fossil fuels. Hydrogen is considered as one of the major energy solutions of the twenty-first century, capable of meeting future energy needs. Being 61a zero-emission fuel, it could reduce environmental impacts and craft novel energy opportunities. Hydrogen through fuel cells can be used in transport and distributed heating, as well as in energy storage systems. The transition from fossil-based fuels to hydrogen requires intensive research to overcome scientific and socio-economic barriers. The purpose of this paper is to reflect the current state, related issues, and projection of hydrogen and fuel elements within the conceptual framework of 61a future sustainable energy vision. An attempt has been made to compile in this paper the past hydrogen-related technologies, present challenges, and role of hydrogen in the future.

Hydrogenation properties and kinetic study of MgH2 - x wt% AC nanocomposites prepared by ball milling

The high de-/hydrogenation temperature of magnesium hydride is still a challenge in solid-state hydrogen storage system for automobiles applications. To improve the hydrogenation properties of MgH_2, we select activated carbon/charcoal (AC) as a catalyst. A systematic investigation was performed on the hydrogen storage behaviors of MgH₂ and MgH₂ - 5 wt% AC nanocomposites, which were prepared by a high-energy planetary ball mill. These synthesized nanocomposites were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscope (HRTEM) for phase identification, surface morphology and microstructural analysis. The pressure-composition-temperature (PCT) isotherm investigation shows the maximum hydrogen storage capacity ~ 6.312 wt% for MgH₂-AC nanocomposites, while 3.417 wt% for MgH₂ at 300 °C. The onset temperature for MgH₂-AC nanocomposites is shifted towards lower side than the 50 h milled MgH₂. The HRTEM study show the activated carbon helps to reduce oxygen from MgO phase in MgH₂, so that significantly improvement achieved in the absorption capacity and kinetics also for the MgH₂-AC nanocomposites. The presence of β- and γ-phases of MgH₂ in MgH₂-AC nanocomposites also supports the high hydrogenation properties and with the support of XRD data.

Characterization of transient cavitation activity during sonochemical modification of magnesium particles

Investigation of the cavitation activity during ultrasonic treatment of magnesium particles during nanostructuring has been performed. Cavitation activity is recorded in the continuous mode after switching the ultrasound on with the use of ICA-5DM cavitometer. It has been demonstrated that this characteristic of the cavitation zone may be varied in a wide range of constant output parameters of the generator. The speed and nature of the cavitation activity alteration depended on the concentration of Mg particles in the suspension and the properties of the medium in which the sonochemical treatment has been performed. Three stages of the cavitation area evolution can be distinguished: 1 - the initial increase in cavitation activity, 2 - reaching a maximum with a subsequent decrease, and 3 - reaching the plateau (or the repeated cycles with feedback loops of enlargement/reduction of the cavitation activity). The ultrasonically treated magnesium particles have been characterized by scanning electron microscopy, X-ray diffraction analysis and thermal analysis. Depending on the nature of the dispersed medium the particles can be characterized by the presence of magnesium hydroxide (brucite) and magnesium hydride. It is possible to reach the incorporation of magnesium hydride in the magnesium hydroxide/magnesium matrix by varying the conditions of ultrasonic treatment (duration of treatment, amplitude, dispersed medium etc.). The influence of the magnesium reactivity is also confirmed by the measurements of cavitation activity in organic dispersed media (ethanol, ethylene glycol) and their aqueous mixtures.

Gaseous complex hydrides NaMH4 and Na2MH5 (M = B, Al) as hydrogen storage materials: a quantum chemical study

Metal hydrides are feasible for energy storage applications as they are able to decompose with hydrogen gas release. In this work, gaseous complex sodium hydrides, NaMH₄ and Na₂MH₅ (M = B or Al), have been investigated using DFT/B3P86 and MP2 methods with 6-311++G(d,p) basis set; the optimized geometry, vibrational spectra and thermodynamic (TD) properties have been determined. Based on TD approach, a stability of the hydrides to different dissociation channels is analysed; the enthalpies of formation ∆_fH°(0) of gaseous species have been obtained: - 1 ± 17 kJ mol^-1 (NaBH₄), 91 ± 14 kJ mol^-1 (NaAlH₄), - 13 ± 16 kJ mol^-1 (Na₂BH₅), and 71 ± 16 kJ mol^-1 (Na₂AlH₅). The complex hydrides are confirmed to produce gaseous products with hydrogen gas release at elevated temperature, whereas heterophase reactions, with NaH and B/Al products in condensed state, are predicted to occur spontaneously at lower temperature. Graphical abstract.

Catalytic dehydrogenation of liquid organic hydrogen carrier dodecahydro-N-ethylcarbazole over palladium catalysts supported on different supports

The system based on liquid organic hydrogen carrier (LOHC) is one of the technologies to solve the problem of hydrogen storage and transportation capacity in large-scale applications. In this paper, the catalytic dehydrogenation of LOHC dodecahydro-N-ethylcarbazole (H12-NEC) over supported Pd nanoparticles (NPs) catalyst on four kinds of different supports, such as Pd/C, Pd/Al₂O₃, Pd/TiO₂, and Pd/SiO₂, was studied. It was found from catalyst characterization and dehydrogenation reaction that the volcano-type dependence of the activity on the Pd particle size, catalytic activity improvement with large specific surface area, and high Pd reduction degree indicated that the structure, particle size, and reduction degree of Pd NPs and textural properties of supports had a synergistic effect on the catalytic performance. Among all the catalysts, Pd/C displayed outstanding catalytic performance with the H12-NEC conversion of 99.9% and hydrogen storage capacity of 5.69 wt% at 180 °C after 12 h. The particle size of Pd/C distributes in the range of 1.5-6.0 nm with an average size of 3.0 nm. The results of dehydrogenation reaction kinetics showed that the rate limiting step and rate constant for different catalysts were mainly related to the physicochemical properties and adsorption and activation abilities towards the reactants and intermediates. In terms of the stationarity of dehydrogenation process, Pd/Al₂O₃ was excellent, indicating that it was best for dehydrogenation of H12-NEC.

Trends and future challenges in hydrogen production and storage research

With the rapid industrialization, increasing of fossil fuel consumption and the environmental impact, it is an inevitable trend to develop clean energy and renewable energy. Hydrogen, for its renewable and pollution-free characteristics, has become an important potential energy carrier. Hydrogen is regarded as a promising alternative fuel for fossil fuels in the future. Therefore, it is very necessary to summarize the technological progress in the development of hydrogen energy and research the status and future challenges. Hydrogen production and storage technology are the key problems for hydrogen application. This study applied bibliometric analysis to review the research features and trends of hydrogen production and storage study. Results showed that in the 2004-2018 period, China, USA and Japan leading in these research fields, the research and development in the world have grown rapidly. However, the development of hydrogen energy still faces the challenge of high production cost and high storage requirements. Photocatalytic decomposition of water to hydrogen has attracted more and more research in hydrogen production research, and the development of new hydrogen storage materials has become a key theme in hydrogen storage research. This study provides a comprehensive review of hydrogen production and storage and identifies research progress on future research trend in these fields. It would be helpful for policy-making and technology development and provide suggestions on the development of a hydrogen economy.

Nanomaterials in the advancement of hydrogen energy storage

The hydrogen economy is the key solution to secure a long-term energy future. Hydrogen production, storage, transportation, and its usage completes the unit of an economic system. These areas have been the topics of discussion for the past few decades. However, its storage methods have conflicted for on-board hydrogen applications. In this review, the promising systems based on solid-state hydrogen storage are discussed. It works generally on the principles of chemisorption and physisorption. The usage of hydrogen packing material in the system enhances volumetric and gravimetric densities of the system and helps in improving ambient conditions and system kinetics. Numerous aspects like pore size, surface area ligand functionalization and pore volume of the materials are intensively discussed. This review also examines the newly developed research based on MOF (Metal-Organic Frameworks). These hybrid clusters are employed for nano-confinement of hydrogen at elevated temperatures. A combination of the various methodologies may give another course to a wide scope in the area of energy storage materials later in the future.

A WS2 Case Theoretical Study: Hydrogen Storage Performance Improved by Phase Altering

Hydrogen is a clean energy with high efficiency, while the storage and transport problems still prevent its extensive use. Because of the large specific surface area and unique electronic structure, two-dimensional materials have great potential in hydrogen storage. Particularly, monolayer 2H-WS₂ has been proven to be suitable for hydrogen storage. But there are few studies concerning the other two phases of WS₂ (1T, 1T') in hydrogen storage. Here, we carried out first-principle calculations to investigate the hydrogen adsorption behaviors of all the three phases of WS₂. Multiple hydrogen adsorption studies also evaluate the hydrogen storage abilities of these materials. Comprehensive analysis results show that the 1T'-WS₂ has better hydrogen storage performance than the 2H-WS₂, which means phase engineering could be an effective way to improve hydrogen storage performance. This paper provides a reference for the further study of hydrogen storage in two-dimensional materials.

The topology impact on hydrogen storage capacity of Sc-decorated ever-increasing porous graphene

Hydrogen storage capacity of different scandium (Sc)-decorated topological porous graphene (PG) was examined through density functional theory calculations. PGs were selected considering odd and even topological symmetries. Our calculations demonstrate that the most preferable sites for adsorption of Sc are located on the center of carbon rings on the perimeter of pores of all sizes. This results in stronger polarization and hybridization perpendicular to the surface leading to enhanced binding. Thus, all PGs are suitable for hydrogen storage under surrounded settings. Furthermore, results showed that the adsorption energies of H₂ molecules increased gradually with the size of pores. Analysis of charge density difference showed that the presence of Sc could play an efficient role for stronger adsorption of hydrogen molecules rather than increasing pore sizes. Furthermore, projected densities of states indicate that favorable systems for hydrogen storage are those that have higher overlap of individual states at Fermi level. Compared with H₂ adsorption on pure graphene, injecting topological defect such as hexagon porous and decoration with a transition metal atom such as Sc can effectively create much more conductive states at Fermi energy. Eventually, Sc decoration leads to n-type doping of PGs that help in much easier transportation of charge carriers and desirable storage of H₂ molecules.

Noble-Metal-Free Ni-W-O-Derived Catalysts for High-Capacity Hydrogen Production from Hydrazine Monohydrate

Development of active and earth-abundant catalysts is pivotal to render hydrazine monohydrate (N₂H₄·H₂O) viable as a hydrogen carrier. Herein, we report the synthesis of noble-metal-free Ni-W-O-derived catalysts using a hydrothermal method in combination with reductive annealing treatment. Interestingly, the thus-prepared Ni-based catalysts exhibit remarkably distinct catalytic properties toward N₂H₄·H₂O decomposition depending upon the annealing temperature. From a systematic phase/microstructure/chemical state characterization and the first-principles calculations, we found that the variation of the apparent catalytic properties of these Ni-based catalysts should stem from the formation of different Ni-W alloys with distinct intrinsic activity, selectivity, and distribution state. The thereby chosen Ni-W alloy nanocomposite catalyst prepared under an optimized condition showed high activity, nearly 100% selectivity, and excellent stability toward N₂H₄·H₂O decomposition for hydrogen production. Furthermore, this noble-metal-free catalyst enables rapid hydrogen production from commercially available N₂H₄·H₂O solution with an intriguingly high hydrogen capacity of 6.28 wt % and a satisfactory dynamic response property. These results are inspiring and momentous for promoting the use of the N₂H₄·H₂O-based H₂ source systems.

Improvement in hydrogen binding ability of closo-dicarboranes via functionalization and designing of extended frameworks

Neutral closo-dicarboboranes are reported to have very low H₂ binding ability. Herein, we report an improvement in H₂ binding energy (E_b) of C₂B₄H₆ by substituting H atoms with different functional groups like X = F, Cl, Br, and XY = BO, CN and NC via quantum-chemical density functional theory based computations. In going from B₆H₆^2- to C₂B₄H₆, the E_b value is reduced from 14.6 kJ mol^-1 to 2.7 kJ mol^-1. C₂B₄X₆ and C₂B₄(XY)₆ systems, which can bind a total of eight H₂ molecules, with one H₂ molecule occupying at each B-B-C face, possess an E_b value per H₂ in the range of 4.5 kJ mol^-1 for X = F, 3.9 kJ mol^-1 for X = Cl, 5.9 kJ mol^-1 for X = Br, 6.8 kJ mol^-1 for XY = BO, 5.8 kJ mol^-1 for XY = CN and 5.2 kJ mol^-1 for XY = NC. The improvement in E_b value is found to be the highest in case of C₂B₄(BO)₆, which has the ability to bind 6.6 gravimetric wt% of H₂. The situation can be made more favorable by applying an external electric field. Energy decomposition analysis reveals that although the dispersion interaction (ca. 55-65%) has significant role in binding H₂ with such types of molecules, contribution from electrostatic and orbital interaction is also considerable. Further, we modeled an extended system by linking C₂B₄(BO)_n through 'C ≡ C' units for H₂ storage purpose. The energy difference between the highest occupied and the lowest unoccupied molecular orbitals gradually lessens with the increase in molecular length. Therefore, it can be tuned gradually by controlling the chain length, which may further open up their potency in the field of electronics. Graphical abstract C₂B₄X₆ (X = F, Cl, Br) and C₂B₄(XY)₆ (XY = BO, CN, NC) show enhanced H₂ binding ability from C₂B₄H₆. Further, 1D, 2D and 3-D frameworks can be built by joining C₂B₄(BO)_n units via 'C ≡ C' linkage.

Theoretical study of hydrogen storage in metal hydrides

Adsorption, absorption and desorption energies and other properties of hydrogen storage in palladium and in the metal hydrides AlH₃, MgH₂, Mg(BH₄)₂, Mg(BH₄)(NH₂) and LiNH₂ were analyzed. The DFT calculations on cluster models show that, at a low concentration, the hydrogen atom remains adsorbed in a stable state near the palladium surface. By increasing the hydrogen concentration, the tetrahedral and the octahedral sites are sequentially occupied. In the α phase the tetrahedral site releases hydrogen more easily than at the octahedral sites, but the opposite occurs in the β phase. Among the hydrides, Mg(BH₄)₂ shows the highest values for both absorption and desorption energies. The absorption energy of LiNH₂ is higher than that of the palladium, but its desorption energy is too high, a recurrent problem of the materials that have been considered for hydrogen storage. The release of hydrogen, however, can be favored by using transition metals in the material structure, as demonstrated here by doping MgH₂ with 3d and 4d-transition metals to reduce the hydrogen atomic charge and the desorption energy.

Cd2SiO4/Graphene nanocomposite: Ultrasonic assisted synthesis, characterization and electrochemical hydrogen storage application

For the first time, a simple and rapid sonochemical technique for preparing of pure Cd₂SiO₄ nanostructures has been developed in presence of various surfactants of SDS, CTAB and PVP. Uniform and fine Cd₂SiO₄ nanoparticle was synthesized using of polymeric PVP surfactant and ultrasonic irradiation. The optimized cadmium silicate nanostructures added to graphene sheets and Cd₂SiO₄/Graphene nanocomposite synthesized through pre-graphenization. Hydrogen storage capacity performances of Cd₂SiO₄ nanoparticle and Cd₂SiO₄/Graphene nanocomposite were compared. Obtained results represent that Cd₂SiO₄/Graphene nanocomposites have higher hydrogen storage capacity than Cd₂SiO₄ nanoparticles. Cd₂SiO₄/Graphene nanocomposites and Cd₂SiO₄ nanoparticles show hydrogen storage capacity of 3300 and 1300 mAh/g, respectively.

Solvent Free Synthesis of PdZn/TiO2 Catalysts for the Hydrogenation of CO2 to Methanol

Catalytic upgrading of CO₂ to value-added chemicals is an important challenge within the chemical sciences. Of particular interest are catalysts which are both active and selective for the hydrogenation of CO₂ to methanol. PdZn alloy nanoparticles supported on TiO₂ via a solvent-free chemical vapour impregnation method are shown to be effective for this reaction. This synthesis technique is shown to minimise surface contaminants, which are detrimental to catalyst activity. The effect of reductive heat treatments on both structural properties of PdZn/TiO₂ catalysts and rates of catalytic CO₂ hydrogenation are investigated. PdZn nanoparticles formed upon reduction showed high stability towards particle sintering at high reduction temperature with average diameter of 3–6 nm to give 1710 mmol kg⁻¹ h of methanol. Reductive treatment at high temperature results in the formation of ZnTiO₃ as well as PdZn, and gives the highest methanol yield.

Hydrogenation of CO2 at ambient pressure catalyzed by a highly active thermostable biocatalyst

BACKGROUND

Replacing fossil fuels as energy carrier requires alternatives that combine sustainable production, high volumetric energy density, easy and fast refueling for mobile applications, and preferably low risk of hazard. Molecular hydrogen (H₂) has been considered as promising alternative; however, practical application is struggling because of the low volumetric energy density and the explosion hazard when stored in large amounts. One way to overcome these limitations is the transient conversion of H₂ into other chemicals with increased volumetric energy density and lower risk hazard, for example so-called liquid organic hydrogen carriers such as formic acid/formate that is obtained by hydrogenation of CO₂. Many homogenous and heterogenous chemical catalysts have been described in the past years, however, often requiring high pressures and temperatures. Recently, the first biocatalyst for this reaction has been described opening the route to a biotechnological alternative for this conversion.

RESULTS

The hydrogen-dependent CO₂ reductase (HDCR) is a highly active biocatalyst for storing H₂ in the form of formic acid/formate by reversibly catalyzing the hydrogenation of CO₂. We report the identification, isolation, and characterization of the first thermostable HDCR operating at temperatures up to 70 °C. The enzyme was isolated from the thermophilic acetogenic bacterium Thermoanaerobacter kivui and displays exceptionally high activities in both reaction directions, substantially exceeding known chemical catalysts. CO₂ hydrogenation is catalyzed at mild conditions with a turnover frequency of 9,556,000 h^-1 (specific activity of 900 µmol formate min^-1 mg^-1) and the reverse reaction, H₂ + CO₂ release from formate, is catalyzed with a turnover frequency of 9,892,000 h^-1 (930 µmol H₂ min^-1 mg^-1). The HDCR of T. kivui consists of a [FeFe] hydrogenase subunit putatively coupled to a tungsten-dependent CO₂ reductase/formate dehydrogenase subunit by an array of iron-sulfur clusters.

CONCLUSIONS

The discovery of the first thermostable HDCR provides a promising biological alternative for a chemically challenging reaction and might serve as model for the better understanding of catalysts able to efficiently reduce CO₂. The catalytic activity for reversible CO₂ hydrogenation of this enzyme is the highest activity known for bio- and chemical catalysts and requiring only ambient temperatures and pressures. The thermostability provides more flexibility regarding the process parameters for a biotechnological application.

Pd Nanoparticles and MOFs Synergistically Hybridized Halloysite Nanotubes for Hydrogen Storage

Natural halloysite nanotubes (HNTs) were hybridized with metal-organic frameworks (MOFs) to prepare novel composites. MOFs were transformed into carbon by carbonization calcination, and palladium (Pd) nanoparticles were introduced to build an emerging ternary compound system for hydrogen adsorption. The hydrogen adsorption capacities of HNT-MOF composites were 0.23 and 0.24 wt%, while those of carbonized products were 0.24 and 0.27 wt% at 25 °C and 2.65 MPa, respectively. Al-based samples showed higher hydrogen adsorption capacities than Zn-based samples on account of different selectivity between metal and hydrogen and approximate porous characteristics. More pore structures are generated by the carbonization reaction from metal-organic frameworks into carbon; high specific surface area, uniform pore size, and large pore volume benefited the hydrogen adsorption ability of composites. Moreover, it was also possible to promote hydrogen adsorption capacity by incorporating Pd. The hydrogen adsorption capacity of ternary compound, Pd-C-H3-MOFs(Al), reached 0.32 wt% at 25 °C and 2.65 MPa. Dissociation was assumed to take place on the Pd particles, then atomic and molecule hydrogen spilled over to the structure of carboxylated HNTs, MOFs, and the carbon products for enhancing the hydrogen adsorption capacity.