A first principles study of hydrogen storage in lithium decorated defective phosphorene

In this study, we studied defect-engineering and lithium decoration of 2D phosphorene for effective hydrogen storage using density functional theory. Contrary to graphene, it is found that the presence of point-defects is not preferable for anchoring of H₂ molecules over defective phosphorene. According to previous research, strategies such as defect engineering, metal decoration, and doping enhance the hydrogen storage capacity of several 2D materials. Our DFT simulations show that point defects in phosphorene do not improve the hydrogen storage capacity compared to pristine phosphorene. However, selective lithium decoration over the defective site significantly improves the hydrogen adsorption capacity yielding a binding energy of as high as ?0.48 eV/H₂ in Li-decorated single vacancy phosphorene. Differential charge densities and projected density of states have been computed to understand the interactions and charge transfer among the constituent atoms. Strong polarization of the H₂ molecule is evidenced by the charge accumulation and depletion. The PDOS shows that the presence of Li leads to enhanced charge transfer. The maximum gravimetric density was investigated by sequentially adding H₂ molecules to the Li-decorated single vacancy defective phosphorene. The Li-decorated single vacancy phosphorene is found to possess a gravimetric density of around 5.3% for hydrogen storage.     

Hydrogen storage in magnesium decorated boron clusters (Mg2Bn,n = 4–14): A density functional theory study

The capacity of hydrogen adsorption of magnesium (Mg) decorated small boron (B) clusters (Mg₂B_n; n = 4–14) was studied using density functional theory (DFT). The calculated results indicate that H₂ adsorbed in the molecular form. The Bader's topological analysis indicates the presence of closed shell type interaction between clusters and H₂ molecules. The clusters are stable even after the adsorption of H₂ molecules. The average energy of H₂ adsorption is calculated to be in the range of 0.13–0.22 eV/H₂. The Mg₂B₆ cluster shows maximum H₂ adsorption (8.10 wt%) at ambient temperature and pressure. Further, we have performed molecular dynamic (MD) simulation at room temperature for each cluster to understand adsorption and desorption of H₂ molecules with time. The MD simulation revealed that most of the adsorbed H₂ molecules moved away from the clusters within 200 fs. However, one H₂ molecule remains attached with the Mg₂B₁₁ cluster even after 200 fs.     

Hydrogen storage systems based on hydride–graphite composites: computer simulation and experimental validation

The design of hydride-based hydrogen storage systems is non-trivial because numerous physical, chemical and engineering principles have to be considered. In particular, gas and heat transport properties of the hydride bed are crucial for a high-dynamic tank operation. Since most hydrides show low intrinsic heat conductivities, auxiliary materials or structures inside the reaction zone are beneficial. For that purpose, hydride–graphite composites with strong anisotropic thermal conductivities have been developed recently.     

Hydrogen storage in Li dispersed graphene with Stone–Wales defects: A first-principles study

Li dispersed graphene with Stone–Wales (SW) defects was investigated for geometric stability and hydrogen storage capability using density functional theory (DFT) calculations. When the graphene with SW defects, which has the internal strain derived from rotated C–C bond, adsorbs Li adatoms, the strain is relieved by generating the buckling of graphene. This effect plays a crucial role in enhancing the binding energy (E_b) of Li adatoms, consequently allowing the atomic dispersion of Li adatoms on the graphene without clustering. The Li dispersed graphene with SW defects can accommodate four H₂ molecules with the range of 0.20–0.35 eV. This falls in a desirable range for feasible applications under ambient conditions. It is therefore anticipated that Li dispersed graphene with SW defects may be an ideal hydrogen storage media due to its geometric stability and high hydrogen storage capacity.     

Potassium decorated γ-graphyne as hydrogen storage medium: Structural and electronic properties

Different sites for K adsorption in γ-graphyne were investigated using density functional theory (DFT) calculations and optical and structural properties of the structures were examined. For the most stable structures, we put one H₂ molecule in different directions on the various sites to evaluate the hydrogen adsorption capability of them. Then, one to nine H₂ molecules in sequence were added to the best structure. Results show that clustering of the K atoms is hindered on the graphyne surface and the most desirable adsorption site for K atom is the hollow site of 12-membered ring with adsorption energy of 5.86 eV. Also, this site is the best site for H₂ adsorption onto K-decorated graphyne with E_das of −0.212 eV. Adding of number of H₂ molecule on this site shows that K atom can bind nine H₂ molecules at one side of the graphyne with the average adsorption energy of 0.204 eV/H₂. Therefore, for one side ca. 8.95 wt % and for both sides of the graphyne with a K atom in each side ca. 13.95 wt % of the hydrogen storage capacity can be achieved. This study shows that K-decorated graphyne can be a promising candidate for the hydrogen storage applications.     

Hydrogen storage via silver–aluminum bimetallic nanoparticle supported on different shapes defect on carbon nanotube

Molecular dynamics simulation has been performed for H2 gas adsorption for silver nanoparticle supported on different shapes of defect in carbon nanotube (CNT). Square, rectangle and line defects in CNT has been investigated for H2 gas adsorption for silver nanoparticle supported on CNT. Different Size of silver nanoparticle, aluminum doping in silver nanoparticle and different temperature has been investigated for H2 storage on silver nanoparticle supported in CNT with different defect shapes. Diffusion coefficient for silver nanoparticle supported on square defect shapes of CNT is more than diffusion coefficient of silver nanoparticle supported on other defect shapes of CNT. Irreversibility structure is observed in silver nanoparticle supported on all shapes defect of CNT and irreversibility structure for silver supported in line defect shapes of CNT is more strong than other defect shapes of CNT. There is none monotonic behavior for H2 adsorption as a function of Aluminum doping on surface of silver-aluminum bimetallic nanocluster on square and line defect shapes of CNT. In current case study, by engineering the size of Aluminum nanoparticle, it is possible to reach certain international standards goals for H2 storage which is set by the United States Department of Energy (DOE).     

Hydrogen energy storage system in a Multi‒Technology Microgrid:technical features and performance

The features and performance of a hydrogen energy storage system included in the microgrid powering a plant for advanced green technologies is presented. The microgrid is powered by a 730–kW photovoltaic source and four energy storage systems. The hydrogen storage system consists of a water demineralizer, a 22.3–kW alkaline electrolyzer generating hydrogen, its AC–DC power supply, 99.9998% hydrogen purifier, 200-bar compressor, 200–L gas storage cylinders, a 31.5–kW proton–exchange–membrane fuel cell running on hydrogen, its DC–AC power conditioning system. The whole system is housed in three containers provided with anti–salt filters to remove brine. The whole system is controlled by the microgrid system supervisor. Operative tests at nominal power show that the round-trip efficiency of the hydrogen energy storage system at full power is ca. 10% in a pure electric operation and ca. 24% in a heat cogeneration operation. At half power these values reduce to 9.5% and 18%, respectively.     

Hydrogen related degradation in pipeline steel: A review

To support our increasing energy demand, steel pipelines are deployed in transporting oil and natural gas resources for long distances. However, numerous steel structures experience catastrophic failures due to the evolution of hydrogen from their service environments initiated by corrosion reactions and/or cathodic protection. This process results in deleterious effect on the mechanical strength of these ferrous steel structures and their principal components. The major sources of hydrogen in offshore/subsea pipeline installations are moisture as well as molecular water reduction resulting from cathodic protection. Hydrogen induced cracking comes into effect as a synergy of hydrogen concentration and stress level on susceptible steel materials, leading to severe hydrogen embrittlement (HE) scenarios. This usually manifests in the form of induced-crack episodes, e.g., hydrogen induced cracking (HIC), stress-oriented hydrogen induced cracking (SOHIC) and sulfide stress corrosion cracking (SSCC). In this work, we have outlined sources of hydrogen attack as well as their induced failure mechanisms. Several past and recent studies supporting them have also been highlighted in line with understanding of the effect of hydrogen on pipeline steel failure. Different experimental techniques such as Devanathan–Stachurski method, thermal desorption spectrometry, hydrogen microprint technique, electrochemical impedance spectroscopy and electrochemical noise have proven to be useful in investigating hydrogen damage in pipeline steels. This has also necessitated our coverage of relatively comprehensive assessments of the effect of hydrogen on contemporary high-strength pipeline steel processed by thermomechanical controlled rolling. The effect of HE on cleavage planes and/or grain boundaries has prompted in depth crystallographic texture analysis within this work as a very important parameter influencing the corrosion behavior of pipeline steels. More information regarding microstructure and grain boundary interaction effects have been presented as well as the mechanisms of crack interaction with microstructure. Since hydrogen degradation is accompanied by other corrosion-related causes, this review also addresses key corrosion causes affecting offshore pipeline structures fabricated from steel. We have enlisted and extensively discussed several recent corrosion mitigation trials and performance tests in various media at different thermal and pressure conditions.     

Hydrogen storage in TiO2 functionalized (10, 10) single walled carbon nanotube (SWCNT) – First principles study

Hydrogen storage in titanium dioxide (TiO₂) functionalized (10, 10) armchair single walled carbon nanotube (SWCNT) is investigated through first principle calculations using density functional theory (DFT). This first principles study uses Vienna Ab-initio Simulation Package (VASP) with ultrasoft pseudopotentials and local density approximation (LDA). The necessary benchmark and other systematic calculations were carried out to project the hydrogen storage capability of the designed system. Interestingly, the TiO₂ molecules functionalized on the outer surface of SWCNT do not undergo any dimerization/clustering thus giving excellent stability and usable gravimetric hydrogen storage capacity of 5.7 wt.% and the value nearly fulfills the US DOE target (i.e. 6 wt.%). The band structure and density of states (DOS) plots suggest that the functionalization can lead a way to transform the nature (metallic → semiconducting) of the pristine SWCNT. The nominal values of H₂ storage capacity and binding energies give much hope for using CNT functionalized with TiO₂ as a practical and reversible hydrogen storage medium (HSM).     

Hydrogen storage comparison of M doped vanadium oxide nanotubes (M = Mo,Zr and W): A molecular simulation study

Zr, Mo and W doped Vanadium oxide nanotube were considered as remarkable materials for hydrogen storage applications. Monte Carlo molecular simulation was performed to study the adsorption behavior of hydrogen molecules on Vanadium oxide nanotubes (VONTs). The effects of temperature, pressure and mole percent of hydrogen on adsorption capacity of VONTs were investigated to provide deep insight of adsorption behavior. The results represented that hydrogen adsorption is an increasing function of pressure and at about 50 MPa all three metal doped VONT has maximum hydrogen capacity. At 5 MPa and room temperature, the hydrogen capacities of Mo, W and Zr doped VONTs were 1.39, 0.88 and 1.43 w% respectively. With temperature increment up to room temperature, more reduction in initial hydrogen capacity were observed in Mo and Zr doped VONTs.Evaluating hydrogen adsorption of Zr doped VONT from pure and hydrogen /nitrogen mixtures at 300 K indicated that under 2 Mpa, modifications in adsorption capacities were insignificant after N2 addition to the environment. Therefore, Zr doped VONT in hydrogen /nitrogen mixture environment can act as a capable adsorbent for Hydrogen storage system in comparison with Mo and W doped VONTs.     

Hydrogen storage in scandium doped small boron clusters (BnSc2, n=3–10): A density functional study

In this work, we present the hydrogen adsorption capacity of Sc doped small boron clusters (B_nSc₂, n = 3–10) using density functional theory. Almost no structural change was observed in the host clusters after hydrogen adsorption. Stabilities of the studied clusters were confirmed by various reactivity parameters such as hardness (η), electrophilicity (ω), and electronegativity (χ). The average adsorption energies was found in the range of 0.08–0.19 eV/H₂ inferring physisorption process, and the fact is also supported by the average distance from Sc to H₂ molecules which was in the range of 2.13 Å-2.60 Å. All the clusters were found to have gravimetric density satisfying the target set by the U.S. Department of Energy (US-DOE) (5.5 wt% by 2020). From Bader's topological analysis, it was confirmed that the nature of interaction was likely to be somewhat closed shell type. ADMP molecular dynamics simulations study was performed at different temperatures to understand the adsorption and dissociation of H₂ from the complexes.     

Hydrogen production from steam gasification of biomass: Influence of process parameters on hydrogen yield – A review

Steam gasification is considered one of the most effective and efficient techniques of generating hydrogen from biomass. Of all the thermochemical processes, steam gasification offers the highest stoichiometric yield of hydrogen. There are several factors which influence the yield of hydrogen in steam gasification. Some of the prominent factors are: biomass type, biomass feed particle size, reaction temperature, steam to biomass ratio, addition of catalyst, sorbent to biomass ratio. This review article focuses on the hydrogen production from biomass via steam gasification and the influence of process parameters on hydrogen yield.     

Hydrogen storage properties and reaction mechanisms of K2Mn(NH2)4–8LiH system

Hydrogen storage properties of K₂Mn(NH₂)₄–8LiH were investigated by considering its de/re-hydrogenation properties and reaction mechanisms. Experimental results show that the dehydrogenated K₂Mn(NH₂)₄–8LiH can be almost re-hydrogenated completely at 230 °C and 50 bar of H₂ with a hydrogenation rate more than 1.0 wt%/min. In-situ synchrotron radiation powder X-ray diffraction (SR-PXD) and FTIR investigations reveal that during ball milling K₂Mn(NH₂)₄ reacts with LiH to form LiNH₂ and K–Mn-species1 which is probably a K–Mn-containing hydride. The ball milled sample releases hydrogen in a multi-step reaction with the formation of K₃MnH₅ and K–Mn-species2 as intermediates and Li₂NH, Mn₃N₂ and MnN as final products. The full hydrogenated products are LiH, LiNH₂, and K–Mn-species2. The K–Mn-species2 may play a critical role for the fast hydrogeneration. This work indicates that transition metal contained amide-hydride composite holds potentials for hydrogen storage.     

A low-cost platinum-free electrocatalyst based on carbon quantum dots decorated Ni–Cu hierarchical nanocomposites for hydrogen evolution reaction

The effective Ni–Cu bimetallic nanocomposite was deposited on a glassy carbon electrode, GCE, that modified with carbon quantum dots, CQDs. The deposition process was done by one-step and controllable electrochemical method in an electrolyte of nickel and copper sulfate. The structural properties of composite studied by techniques such as X-ray diffraction, XRD, energy dispersive X-ray analysis, EDX, field emission scanning electron microscopy, FESEM, and transmission electron microscopy, TEM. Ni–Cu/RCQDs nanocomposite was applied as a cathode for catalysis of hydrogen evolution reaction, HER, in acidic media by cyclic voltammetry, CV, linear sweep voltammetry, LSV, chronoamperometry, CA, and electrochemical impedance spectroscopy, EIS. The onset potential, E_onset, for the evolution of hydrogen at the current density of −10 mA cm⁻² for Ni–Cu/RCQDs was −230 mV vs. SHE that had a 100 mV shift to positive voltages in comparison with Ni–Cu catalyst. It can be related to the synergistic effect between metallic nanoparticles. V. dec⁻¹, respectively.     

A porous 3d-4f heterometallic metal–organic framework for hydrogen storage

A heterometallic metal–organic framework, {[Ce(oda)₃Zn_1.5(H₂O)₃]·0.75H₂O}_n (1, H₂oda = oxydiacetic acid), has been synthesized under hydrothermal condition. The single-crystal X-ray diffraction analysis reveals that compound 1 belongs to hexagonal crystal system with space group P6/mcc and exhibits 3D porous framework. The hydrogen adsorption experiments suggest that 1 possesses reversible hydrogen storage capacity, up to 1.34 wt.% at 77 K and 0.86 wt.% at 298 K, respectively.     

Hydrogen storage properties of 2Mg–Fe mixtures processed by hot extrusion: Influence of the extrusion ratio

Hot extrusion processing was employed to produce 2Mg–Fe bulk mixtures for hydrogen storage. 2Mg–Fe powder mixtures were prepared by high-energy ball milling. These mixtures were cold pressed into cylindrical pre-forms, which were then processed by hot extrusion (at 300 °C) to produce bulks. In this work, we analyzed the influence of the extrusion ratio (3/1, 5/1 and 7/1) on the sorption properties of the bulks. The nanometric grain size remained unaltered after all hot extrusion conditions. More porous bulks were produced at an extrusion ratio of 3/1. In the first cycle of hydrogenation, the sample processed at 3/1 absorbed more hydrogen (4 wt% of H) than the precursor powders (3 wt% of H). The results showed that the desorption temperature of bulks were very similar to that of 2Mg–Fe powders, which is good considering the lower surface area of bulks, and that samples with Fe in excess presented lower desorption temperatures.