Improved Hydrogen Sorption Research Articles

XPS Investigation on Improving Hydrogen Sorption Kinetics of the KSiH3 System by Using Zr-Based Catalysts.

The superior hydrogen storage properties makes the KSiH3 system a potential hydrogen storage material for practical applications. A theoretical capacity of 4.3 wt% bring this material to the front line of all the available hydrogen storage materials; however, the activation barrier of the reaction restricts the system to absorb and desorb hydrogen reversibly at elevated temperatures even if the thermodynamics suggest its room temperature operation. Several catalysts have already been tested to enhance its kinetic properties. In this work, the efforts were made to reduce the activation energy by using Zr-based catalysts to the KSi/KSiH3 system. The value of activation energy was found to be lowest (i.e., 87 kJ mol-1) for the ZrH2-added KSiH3 system. The mechanism of this improvement was investigated by using X-ray photoelectron spectroscopy (XPS).

Architecturally robust tubular nano-clay grafted Li0.9Ni0.5Co0.5O2-x/LiFeO2 nanocomposites: New implications for electrochemical hydrogen storage

To meet the demand for sustainable energy development, focusing on storage systems of clean energy like hydrogen is a priority. However, the utilization of new sorbent materials for an in-depth understanding of hydrogen storage mechanisms remains lacking. Herein, a novel composite electrode based on halloysite nanotube-Li0.9Ni0.5Co0.5O2-x/LiFeO2 (HNT-LNCO/LFO) nanostructures with superior electrochemical hydrogen storage behavior is developed via two-pot synthesis strategy, in which the HNT bridges with rich active sites serve as a natural clay support for LNCO/LFO electrocatalysts to equip improved hydrogen sorption kinetics through the spillover phenomena and redox coupling effect. Varied parameters, such as fuel types, the molar ratio of fuel to nitrates, the concentration of the LNCO/LFO (mg/ml), and solvent were optimized to prepare HNT-LNCO/LFO nanocomposites with desired purity, structure, and morphology. These physicochemical changes were realized by a combination of X-ray Powder Diffraction (XRD), Field Emission Scanning Electron Microscopy (FE-SEM), High Resolution Transmission Electron Microscopy (HR-TEM), and Brunauer-Emmett-Teller (BET) analyses. Furthermore, the electrochemical nature of the proposed nanocomposites were probed by cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry charge–discharge (CCD) process in KOH medium. The effect of conductive LNCO/LFO contents (3.0 %, 5.0 % and 7.0 %) on the HNT substrate was evaluated with the discharge efficiency and hydrogen spillover mechanism. As a consequence, the LNCO/LFO nanoparticles and pristine HNT structures exhibited the hydrogen storage capacities of 499.67 and 84.05 mAhg−1 after 15 cycles, respectively. However, the contribution of LNCO/LFO nanoparticles with weight percent of 3.0 %, 5.0 % and 7.0 % in tubular matrix can produce the discharge efficiencies of 309.33, 437.34 and 132.25 mAhg−1 in three electrode cells, respectively. This systematic work will result in alternative insights of the well-designed HNT-based nanocomposites for highly efficient energy storage applications.

An alternative platform of solid-state hydrides with polymers as composite/encapsulation for hydrogen storage applications: Effects in intermetallic and complex hydrides

Hydrogen energy proved the remarkable benefits from the perspective of future energy needs and environmental concerns. However, the existing challenges in hydrogen energy technologies, mainly hydrogen storage need to be overcome. In hydrogen storage systems, metal hydrides are highly suffered by the protic species and oxygen because of their reactivity in ambient conditions, leading to surface contamination and affecting the hydrogen sorption behaviors. Moreover, the hydrogen storage in metal hydrides can be hindered by impurities such as CO and CO2 in hydrogen gas. The new concepts of hydrides with polymers are vital for overcoming the hydrides’ contamination-related issues. This comprehensive review spotlight primarily on the alternative ways to avoid the contamination of hydrides with polymers. The researchers worldwide developed different concepts of polymer-hydrides (intermetallic and complex hydrides) systems, mainly composites and polymer encapsulation methods, to avoid contamination from the air/moisture/gas impurities and improve hydrogen sorption properties in hydrides. Interestingly, selective gas properties of polymers with hydrides show tremendous advantages because of their selective permeability of hydrogen, which influences the easier path for hydrogen diffusion to form the hydrides through the polymer matrix and prohibit the contamination of hydride materials from the other gases/protic species. Notably, this review bridges the understanding between the polymers and hydrides (intermetallic, complex and reactive hydride composite) for hydrogen storage systems.

Hydrogen storage properties of magnesium hydride catalyzed by Ni-based solid solutions

The Ni–25%X (X=Fe, Co, Cu, molar fraction) solid solutions were prepared and then doped into MgH2 through high-energy ball milling. The initial dehydrogenation temperatures of MgH2/Ni–25%X composites are all decreased by about 90 °C relative to the as-milled pristine MgH2. The Ni–25%Co solid solution exhibits the most excellent catalytic effect, and the milled MgH2/Ni–25%Co composite can release 5.19 wt.% hydrogen within 10 min at 300 °C, while the as-milled pristine MgH2 can only release 1.78 wt.% hydrogen. More importantly, the dehydrogenated MgH2/Ni–25%Co composite can absorb 5.39 wt.% hydrogen at 275 °C within 3 min. The superior hydrogen sorption kinetics of MgH2/Ni–25%Co can be ascribed to the actual catalytic effect of in-situ formed Mg2Ni(Co) compounds. First-principles calculations show that the hydrogen absorption/desorption energy barriers of Mg/MgH2 systems decrease significantly after doping with transition metal atoms, which interprets well the improved hydrogen sorption properties of MgH2 catalyzed by Ni-based solid solutions.

Improved hydrogen sorption properties of Pd in protic and aprotic ionic liquids effected by superacid addition

The mixtures of selected protic and aprotic ionic liquids with their parent superacids were used as electrolytes in the process of hydrogen electrosorption in thin (ca. 0.5 µm) Pd films. The properties of ionic liquids and their mixtures with superacids were characterized with the use of electrochemical and physicochemical methods to show the perspectives of their potential utilization as electrolytes in hydride/protonic systems. Based on the electrochemical studies it was possible to estimate the minimum concentrations of the superacids in protic and aprotic ionic liquids which give maximum hydrogen absorption capacities in Pd (H/Pd). Unusual, previously unnoticed ‘two-step’ α→β phase transition was observed on the hydrogen electrosorption isotherm of Pd for the process of hydrogen absorption from the protic ionic liquids for some superacid concentrations. 1H NMR spectroscopy of the protic ionic liquids enables to discuss the relation between proton mobility and hydrogen electrosorption properties.

Catalytic mechanism of TiO2 quantum dots on the de/re-hydrogenation characteristics of magnesium hydride

In the present study, the catalyst anatase titanium dioxide (TiO2) quantum dots (QDs) of size ∼ (2.50–4.00)nm was successfully synthesized by the hydrothermal method. The formation of TiO2: QDs has been established by UV–Vis spectroscopy and confirmed by transmission electron microscopy. Here, we report the catalytic action of TiO2:QDs on de/re-hydrogenation properties of magnesium hydride (MgH2/Mg). By catalyzing MgH2 through this catalyst, the onset desorption temperature of MgH2 gets reduced significantly from ∼360 °C (for ball-milled MgH2) to ∼260 °C. Moreover, the Mg-TiO2: QDs sample absorbed a significant amount of hydrogen up to ∼6.10 wt% in just 77sec at 280 °C. Improved rehydrogenation kinetics has been found even at lower temperatures by absorbing ∼5.30 wt% in 74 s at 225 °C and ∼5.0 wt% of hydrogen in 30 min at 100 °C. Based on structural,.microstructural, and XPS investigations, a feasible mechanism for improved hydrogen sorption and cyclic stability in MgH2 catalyzed with TiO2:QDs has been explained and discussed. To our knowledge, no studies have been carried out on the sorption of hydrogen in MgH2 catalyzed by TiO2:QDs.

The effect of Na addition on the first hydrogen absorption kinetics of cast hypoeutectic Mg–La alloys

With superior properties of Mg such as high hydrogen storage capacity (7.6 wt% H/MgH2), low price, and low density, Mg has been widely studied as a promising candidate for solid-state hydrogen storage systems. However, a harsh activation procedure, slow hydrogenation/dehydrogenation process, and a high temperature for dehydrogenation prevent the use of Mg-based metal hydrides for practical applications. For these reasons, Mg-based alloys for hydrogen storage systems are generally alloyed with other elements to improve hydrogen sorption properties. In this article, we have added Na to cast Mg–La alloys and achieved a significant improvement in hydrogen absorption kinetics during the first activation cycle. The role of Na in Mg–La has been discussed based on the findings from microstructural observations, crystallography, and first principles calculations based on density functional theory. From our results in this study, we have found that the Na doped surface of Mg–La alloy systems have a lower adsorption energy for H2 compared to Na-free surfaces which facilitates adsorption and dissociation of hydrogen molecules leading to improvement of absorption kinetic. The effect of Na on the microstructure of these alloys, such as eutectic refinement and a density of twins is not highly correlated with absorption kinetics.

Improving hydrogen sorption performances of MgH2 through nanoconfinement in a mesoporous CoS nano-boxes scaffold

For the first time, structure-modified CoS-nanoboxes (CoS-NBs) scaffold as a multifunctional Supporting material has been developed by using a template-consumption method for nanoconfinement of MgH2 particles within its mesoporous structure (denoted as MgH2@CoS-NBs). Microstructural observations via transmission electron microscopy (TEM) reveal the uniform distribution of MgH2 nanocrystals within the mesoporous networks of CoS-NBs scaffold and the surface decoration of MgH2 crystals by in-situ formed MgS phase. The peculiar core-shell structured morphology of MgH2 nanocrystals and the “nano-size effect” notably enhances the thermodynamic properties of MgH2 through the reduction in hydriding and dehydriding enthalpies (−65.6 ± 1.1 and 68.1 ± 1.4 kJ mol−1 H2, respectively). Moreover, the improved hydrogen sorption kinetics can be attributed to the catalytic effect of MgS through reducing the intrinsic kinetic energy barriers for both hydriding and dehydriding (57.4 ± 2.2 and 120.8 ± 3.2 kJ mol−1 H2, respectively). The “nano-size effect” of nanoconfined Mg/MgH2 crystals, the catalyzing effect of MgS and the multifunctional role of CoS-NBs scaffold are likely to be synergistically contributed to the superior hydrogen sorption performances of MgH2@CoS-NBs composite, as compared to the pure MgH2.

Improve hydrogen sorption kinetics of MgH2 by doping carbon-encapsulated iron-nickel nanoparticles

Magnesium hydride (MgH2) with excellent hydrogen absorption kinetics is important for the wide application of hydrogen energy. Herein, to accelerate the sorption kinetics of MgH2 and lower its dehydrogenation temperature, we design and prepare a carbon film coated dual transition metal alloy, the Fe0.64Ni0.36@C composite with a core-shell structure, and employ it as an additive to synthesize MgH2–Fe0.64Ni0.36@C system by ball-milling and hydriding combustion method. In contrast to pure MgH2, the initial hydrogen release temperature of the MgH2–Fe0.64Ni0.36@C composite lowers to 250 °C from 378 °C and the composite can absorb 5.18 wt% H2 within 20 min (150 °C, 3 MPa H2). More importantly, the apparent activation energy of the dehydrogenation for decomposition of Fe0.64Ni0.36@C-doped MgH2 reduced from 162.8 ± 8.3 kJ/mol to 86.9 ± 4.6 kJ/mol. The enhanced hydrogen sorption kinetics of MgH2–Fe0.64Ni0.36@C mainly attributes to the synergistic effect between the formed Fe@C and Mg2Ni/Mg2NiH4. Moreover, the MgH2 co-doped with the multiple in-situ formed active particles shows excellent cycling performance, indicative of potential application in practical hydrogen storage in the near future.

Improved hydrogen sorption kinetics of compacted LiNH2–LiH based small hydrogen storage tank by doping with TiF4 and MWCNTs

Abstract Kinetic properties of compacted LiNH2–LiH developed by doping with TiF4 and multi-walled nanotubes (MWCNTs) as well as upscaling to small hydrogen storage tank are proposed. During de/rehydrogenation, transition metal-based catalyst (TiF4) provides the catalytic effects on hydrogen dissociation/recombination, while MWCNTs benefit thermal conductivity and hydrogen permeability. Enhanced dehydrogenation kinetics is observed from single-step reaction at narrower and lower temperature range of 150–350 °C (100 °C lower than the compacted LiNH2–LiH without additives) together with long plateau temperature and constant hydrogen flow rate (50 SCCM) up to 30 min during desorption of the small tank. Hydrogen contents de/absorbed during 5–6 cycles increase from 1.90-2.40 to 3.10-4.70 wt % H2 (from 29 to up to 80% of theoretical capacity). Li5TiN3 detected upon cycling absorbs NH3 to form Li5TiN3(NH3)x, favoring hydrogen sorption properties of LiNH2–LiH system. Moreover, comparable reaction mechanisms and performances are found at different positions inside the tank of compacted LiNH2–LiH doped with TiF4 and MWCNTs.

Hydrogen desorption/absorption properties of the extensively cold rolled β Ti–40Nb alloy

β Ti–Nb BCC alloys are potential materials for hydrogen storage in the solid state. Since these alloys present exceptional formability, they can be processed by extensive cold rolling (ECR), which can improve hydrogen sorption properties. This work investigated the effects of ECR accomplished under an inert atmosphere on H2 sorption properties of the arc melted and rapidly solidified β Ti40Nb alloy. Samples were crushed in a rolling mill producing slightly deformed pieces within the millimeter range size, which were processed by ECR with 40 or 80 passes. Part of undeformed fragments was used for comparison purposes. All samples were characterized by scanning electron microscopy, x-ray diffractometry, energy-dispersive spectroscopy, hydrogen volumetry, and differential scanning calorimetry. After ECR, samples deformed with 40 passes were formed by thick sheets, while several thin layers composed the specimens after 80 passages. Furthermore, deformation of β Ti–40Nb alloys synthesized samples containing a high density of crystalline defects, cracks, and stored strain energy that increased with the deformation amount and proportionally helped to overcome the diffusion's control mechanisms, thus improving kinetic behaviors at low temperature. Such an improvement was also correlated to the synergetic effect of resulting features after deformation and thickness of stacked layers in the different deformation conditions. At the room temperature, samples deformed with 80 passes absorbed ∼2.0 wt% of H2 after 15 min, while samples deformed with 40 passes absorbed ∼1.8 wt% during 2 h, excellent results if compared with undeformed samples hydrogenated at 300 °C that acquired a capacity of ∼1.7 wt% after 2 h. The hydrogen desorption evolved in the same way as for absorption regarding the deformation amount, which also influenced desorption temperatures that were reduced from ∼270 °C, observed for the undeformed and samples deformed with 40 passes, to ∼220 °C, for specimens rolled with 80 passes. No significant loss in hydrogen capacity was observed in the cold rolled samples.

Improved hydrogen sorption kinetics in Mg modified by chosen catalysts

Hydrogen sorption characteristics were investigated in Mg modified by ten chosen catalyzing additives X = Mg2Si, Mg2Ge, Mg17Al12, Mg5Ga2, NaCl, LiCl, NaF, LiF and by two combinations Ni + Mg17Al12 and Ni + Mg2Si. Amorphous carbon (CB) was used as an anti-sticking component. It was found that optimum content of both X and CB was between 10 and 14 wt %. To assess the effect of X itself upon the sorption kinetics, concentration of both X and CB was fixed to about 12 wt %. The shortest desorption times t09 (time to desorption of 90 pct of stored hydrogen) showed alloys with X = NaF, Mg2Si, Mg2Ge and NaCl. Careful measurements of equilibrium hydrogen pressure, peq, at 623 K showed an increase in peq for added chlorides, fluorides, Mg2Ge and also for Mg2Si. TPD experiments revealed desorption peaks for X = NaCl, LiF shifted down to temperatures as low as 597 K.

Nanostructured hydrogen storage materials prepared by high-energy reactive ball milling of magnesium and ferrovanadium

Hydrogen storage nanocomposites prepared by high energy reactive ball milling of magnesium and vanadium alloys in hydrogen (HRBM) are characterised by exceptionally fast hydrogenation rates and a significantly decreased hydride decomposition temperature. Replacement of vanadium in these materials with vanadium-rich Ferrovanadium (FeV, V80Fe20) is very cost efficient and is suggested as a durable way towards large scale applications of Mg-based hydrogen storage materials. The current work presents the results of the experimental study of Mg–(FeV) hydrogen storage nanocomposites prepared by HRBM of Mg powder and FeV (0–50 mol.%). The additives of FeV were shown to improve hydrogen sorption performance of Mg including facilitation of the hydrogenation during the HRBM and improvements of the dehydrogenation/re-hydrogenation kinetics. The improvements resemble the behaviour of pure vanadium metal, and the Mg–(FeV) nanocomposites exhibited a good stability of the hydrogen sorption performance during hydrogen absorption – desorption cycling at T = 350 °C caused by a stability of the cycling performance of the nanostructured FeV acting as a catalyst. Further improvement of the cycle stability including the increase of the reversible hydrogen storage capacity and acceleration of H2 absorption kinetics during the cycling was observed for the composites containing carbon additives (activated carbon, graphite or multi-walled carbon nanotubes; 5 wt%), with the best performance achieved for activated carbon.

TiF3 catalyzed MgH2 as a Li/Na ion battery anode

MgH2 has been considered as a potential anode material for Li ion batteries due to its low cost and high theoretical capacity. However, it suffers from low electronic conductivity and slow kinetics for hydrogen sorption at room temperature that results in poor reversibility, cycling stability and rate capability for Li ion storage. This work presents a MgH2–TiF3@CNT based Li ion battery anode manufactured via a conventional slurry based method. Working with a liquid electrolyte at room temperature, it achieves a high capacity retention of 543 mAh g−1 in 70 cycles at 0.2 C and an improved rate capability, thanks to the improved hydrogen sorption kinetics with the presence of catalytic TiF3. Meanwhile, the first realization of Na ion uptake in MgH2 has been evidenced in experiments.

Hydrogen storage in Mg2Ni(Fe)H4 nano particles synthesized from coarse-grained Mg and nano sized Ni(Fe) precursor.

In this work, Mg2Ni(Fe)H4 was synthesized using precursors of nano Ni(Fe) composite powder prepared through arc plasma method and coarse-grained Mg powder. The microstructure, composition, phase components and the hydrogen storage properties of the Mg–Ni(Fe) composite were carefully investigated. It is observed that the Mg2Ni(Fe)H4 particles formed from the Mg–Ni(Fe) composite have a diameter of 100–240 nm and a portion of Fe in the Ni(Fe) nano particles transformed into α-Fe nano particles with the diameter of 40–120 nm. DSC measurements showed that the peak desorption temperature of the Mg2Ni(Fe)H4 was reduced to 501 K and the apparent activation energy for hydrogen desorption of the Mg2Ni(Fe)H4 was 97.2 kJ mol−1 H2. The formation enthalpy of Mg2Ni(Fe)H4 was measured to be −53.1 kJ mol−1 H2. The improvements in hydrogen sorption kinetics and thermodynamics can be attributed to the catalytic effect from α-Fe nano particles and the destabilization of Mg2NiH4 caused by the partial substitution of Ni by Fe, respectively.

Hydrogen storage properties of core-shell structured Mg@TM (TM = Co, V) composites

Target improving the hydrogen sorption properties of Mg, core-shell structured Mg@TM (TM = Co, V) composites were synthesized via an approach combining arc plasma method and electroless plating. The core-shell structures with the MgH2 core and V or Co containing hydride shells for hydrogenated Mg@TM particles were observed through HAADF-STEM and HRTEM techniques. The measured hydrogenation enthalpy (ΔHabs = −70.02 kJ/mol H2) and activation energy (Ea = 67.66 kJ/mol H2) of the ternary Mg@Co@V composite were lower than those of binary composites and the pure Mg powder. In addition, the onset dehydrogenation temperature for the hydrogenated ternary composite measured from DSC was 323 °C, about 60 °C lower than that of pure MgH2. On one hand, these improved properties can be attributed to the core-shell structure which may introduce more contacts between catalysts and Mg, thus providing more nucleation sites for hydrogen sorption. On the other hand, the co-effect of MgCo hydrides (Mg2CoH5&Mg3CoH5) acting as “hydrogen pump” and V2H accelerating the dissociation of H2 might also contribute to the improved hydrogen sorption properties of Mg.

Hydrogenation and electrochemical studies of La–Mg–Ni alloys

La–Mg–Ni alloys are potential candidates for hydrogen storage materials. In this study, mechanical alloying with subsequent annealing under an argon atmosphere at 973 K for 0.5 h, were used to produce La2-xMgxNi7 alloys (x = 0, 0.25, 0.5, 0.75, 1). Shaker type ball mill was used. An objective of the present study was to investigate an influence of amount of Mg in alloy on electrochemical, hydrogenation and dehydrogenation properties of La–Mg–Ni materials. X-ray diffraction analyses revealed formation of material with multi-phase structure. Obtained materials were studied by a conventional Sievert's type device at 303 K. It was observed that electrochemical discharge capacity and gaseous hydrogen storage capacity of La–Mg–Ni alloys increases with Mg content to reach maximum for La1.5Mg0.5Ni7 alloy. Moreover, all of La–Mg–Ni alloys were characterized by improved hydrogen sorption kinetics in comparison to La–Ni alloy.

Enhancement of Hydrogen Storage in Destabilized LiNH2 with KMgH3 by Quick Conveyance of N-Containing Species

The advantage of potassium–magnesium bimetallic hydride as novel destabilization agent for LiNH2 is demonstrated by a comparative study among MgH2-, NaMgH3-, and KMgH3- systems. LiNH2 combined with KMgH3 not only results in a substantial decreased desorption temperature by >60 °C and suppression of NH3 release but also enhances sorption kinetics two to five times in comparison with the single MgH2 or NaMgH3. A high reversible capacity of >65% is also achieved, even recharging under milder conditions. Through detailed structural analysis on the desorption products in various stages of these combined systems, we proposed a “self-concerted” reaction mechanism in which the in situ formed active MgH2 and KH by KMgH3 are involved in LiNH2 decomposition. In addition, the remarkable promotion in conveyance of N-containing species by highly active KH compared with NaH is believed to be responsible for the superior destabilizing effect of KMgH3 over NaMgH3 in improving hydrogen sorption kinetics of LiNH2.

Nanostructured Mg based hydrogen storage bulk materials prepared by high pressure torsion consolidation of arc plasma evaporated ultrafine powders

Nanostructured Mg based bulk materials were prepared using a new processing route: consolidation by high pressure torsion (HPT) of ultrafine powders obtained by arc plasma method. The bulk material was mainly composed of ultrafine Mg grains and dispersed nanosized MgO. In comparison to pure Mg ultrafine powders prepared using only arc plasma method, the hydrogenation enthalpy was slightly increased and the absorption activation energy was reduced through the HPT treatment. The structure refinement and the fragmentation of the MgO layer induced by the HPT account for the improved hydrogen sorption thermodynamic and kinetic properties. The additions of Ni catalyst nano-powders reduced the storage capacity but improve the reaction kinetics and lowered the temperature for storage. Comparatively, the alloying by Fe had little beneficial effect because the Fe nano-powder did not deform plastically and remained unaltered under HPT.

Preparation and hydrogen sorption properties of a Ni decorated Mg based Mg@Ni nano-composite

For the first time, a nano Ni decorated Mg ultrafine powder, Mg@Ni nano-composite powder, was prepared through arc plasma evaporation of pure Mg followed by the electroless plating of Ni on the Mg ultrafine particles in a NiCl2 solution. The phase components, microstructure and hydrogen sorption properties of the Mg@Ni composite powder were carefully investigated. It is observed that the composite is mainly composed of ultrafine Mg particles decorated by nano Ni grains introduced during electroless plating. Based on the Pressure-Composition-Temperature measurements, the hydrogenation enthalpy of the Mg@Ni composite is determined to be −73.6 kJ/mol H2, close to that of pure Mg. Meantime, the hydrogen absorption kinetics can be improved and the hydrogen desorption temperature of the hydrogenated Mg@Ni nano-composite can be reduced as compared to those of the pure Mg ultrafine powder. The improved hydrogen sorption properties can be mainly attributed to the gateway effects from the Mg2Ni/Mg2NiH4 phases formed on Mg/MgH2 ultrafine particles after re-/dehydrogenation cycles. The results showed that through arc plasma method followed by electroless plating of transition metals, the hydrogen storage properties of Mg ultrafine powders can be effectively improved.