Hydrogen Sorption Characteristics Research Articles

Phase formation behavior and hydrogen sorption characteristics of TiFe0.8Mn0.2 powders prepared by gas atomization

In this article we have investigated the phase formation behavior and hydrogen storage characteristics of TiFe0.8Mn0.2 samples produced by electrode induction melting gas atomization (EIGA) as well as conventional vacuum arc-melting (VAM). TiFe (46Ti–46Fe–8Mn (wt%) with cubic, CsCl-type structure) and C14 Laves (37Ti–51Fe–12Mn (wt%) with hexagonal, MgZn2-type structure) phases were detected in both atomized powders and crushed ingots, the latter possessing a lower fraction of Laves phase. Microstructural characterization included electron probe micro-analysis (EPMA) and transmission electron microscopy (TEM), which evidenced the existence of a non-equilibrium Ti2Fe phase in the atomized powders. The formation of this additional secondary phase was attributed to the rapid cooling rate during powder manufacturing, based on earlier findings and phase formation thermodynamic calculations combined with Scheil solidification simulations. In addition, kinetics and pressure-composition isotherms (PCIs) were acquired to determine both absorption and desorption enthalpy/entropy, as well as to study the influence of the synthesis route (and hence the resulting microstructure) on kinetics, thermodynamics and reaction mechanisms of the TiFe0.8Mn0.2 alloy.

The adaptable effect of Ru on hydrogen sorption characteristics of the MgH2 system

In this study, a MgH2–Ru composite is prepared by mechanical ball milling of MgH2 and Ru powders. The microstructural analysis revealed the uniform distribution of Ru nanoparticles in the MgH2 matrix and the formation of intermetallic compounds (i.e. Mg6.2Ru and Mg1.5Ru) after dehydrogenation of the composite. The substantial improvements in the de/hydrogenation properties of MgH2 are due to the adjustable catalytic role of Ru under low temperature and pressure conditions. MgH2–Ru composite started to release hydrogen at an onset temperature of 300 °C, much lower than the mechanically milled pure MgH2 (350 °C). Hydrogen absorption of the MgH2–Ru composite is relatively fast at 350 °C and stored 6.1 wt% in 5 min. At the same temperature, the hydrogenated MgH2–Ru composite released all stored hydrogen in less than 5 min. Compared with the catalyst-free MgH2, the hydrogenation and dehydrogenation activation energies of the MgH2–Ru composite are reduced to 65.12 ± 2.4 kJ/mol H2, and 97.46 ± 4.15 kJ/mol H2, respectively. In addition, it further demonstrated how the reversible transformation of Mg–Ru intermetallic phases induces the thermodynamic destabilization of the MgH2 system. The presence of Ru not only facilitated the breaking of the Mg–H bond but also provided very good catalytic interfaces for enhanced de/hydrogenation properties of MgH2.

Superior hydrogen performance of in situ formed carbon modified MgH2 composites.

The MgH2-carbonic combustion product of the anthracene (CCPA) composite was synthesized by hydrogen combustion and mechanically ball-milled method to simultaneously achieve confinement by the in situ formed amorphous carbon. The amorphous carbon derived from the carbonic combustion product of anthracene in the MgH2-CCPA composite led to a significant increase in hydrogen sorption characteristics. The onset dehydrogenation temperature for the MgH2-CCPA composite was reduced to 589 K, which was 54 K less than that of pure milled MgH2. Regarding dehydrogenation kinetics, the MgH2-CCPA composite could release 5.933 wt% H2 within 3000 s at 623 K, while only 3.970 wt% H2 was liberated from the as-milled MgH2 within 3000 s at the same temperature. The MgH2-CCPA composite also exhibited excellent hydrogenation characteristics, absorbing 3.246 wt% of hydrogen within 3000 s at 423 K, which was three times higher than 0.818 wt% uptaken by the pure MgH2. The apparent activation energy (E a) for the dehydrogenation of the MgH2-CCPA composite was significantly reduced from 161.1 kJ mol-1 to 77.5 kJ mol-1. The notable improvement in sorption kinetics of the MgH2-CCPA nanocomposite is ascribed to the in situ formed amorphous carbon during the hydrogenation/dehydrogenation process.

Experimental hydrogen sorption study on a LaNi5-based 5 kg reactor with novel conical fins and water tubes and its numerical scale-up through a modular approach

Hydrogen sorption characteristics of 5 kg-LaNi5 reactor featuring conical fins and heat transfer tubes is experimentally studied at various water flow rates (Vs:2.5, 5, 7 LPM), inlet temperatures (Ts:30, 25, 20 °C), hydrogen pressures (Ps:10, 15, 20, 25 bar). Higher Vs, Ps, and lower Ts yield faster absorption through higher driving force (∝ln (Ps/Peq), Peq: equilibrium pressure). Ninety percent absorption takes ∼12.3 and ∼13.7 min at Vs:7 and 2.5 LPM (Ps:15 bar, Ts:30 °C). Faster atmospheric desorption needs higher Ts and/or Vs offering higher driving force (∝ (1-(1/Peq)). 90% desorption takes ∼20.1 and ∼21.8 min for initial bed temperatures of 60 and 30 °C, (Vs:5 LPM, Ts:60 °C). Absorption of this ‘Single Reactor’ and five/ten (25/50 kg) such reactors in series and parallel are studied numerically. Series configuration stores five/ten-times hydrogen than ‘Single Reactor’ within the same duration by doubling/tripling Vs (same Ps, Ts). Parallel configuration requires proportional water supply.

Characterization of Mg2NiH4 type hydrides by TEM

Mixtures of corresponding metals with composition 95 wt% Mg2.05Ni0.7V0.3 and Mg2.1Ni0.7V0.3 and with addition of 5 wt% of activated carbon derived from apricot stones are prepared by ball milling under argon atmosphere. The received mixtures are tested for their hydrogen sorption characteristics at different temperatures. TEM characterization of these materials poses some challenges, because of their sensitivity to oxidation and the high energy of the electron beam exposure, which could cause negative impact. After hydriding at 300 °C and 1 MPa TEM results (SAED, HRTEM) showed the following phase composition: monoclinic and orthorhombic Mg2NiH4, MgO, VHx and graphite for both samples.

Chemomechanical effect of reduced graphene oxide encapsulation on hydrogen storage performance of Pd nanoparticles

The chemomechanical effect of rGO/Pd/rGO nanolaminates is studied, which related the hydrogen sorption characteristics with nanoconfinement. Results of this study open an interesting avenue for tuning the hydrogen storage performance of metal hydrides.

Elucidating the Effects of the Composition on Hydrogen Sorption in TiVZrNbHf-Based High-Entropy Alloys.

A number of high-entropy alloys (HEAs) in the TiVZrNbHf system have been synthesized by arc melting and systematically evaluated for their hydrogen sorption characteristics. A total of 21 alloys with varying elemental compositions were investigated, and 17 of them form body-centered-cubic (bcc) solid solutions in the as-cast state. A total of 15 alloys form either face-centered-cubic (fcc) or body-centered-tetragonal (bct) hydrides after exposure to gaseous hydrogen with hydrogen per metal ratios (H/M) as high as 2.0. Linear trends are observed between the volumetric expansion per metal atom [(V/Z)fcc/bct – (V/Z)bcc/hcp]/(V/Z)bcc/hcp with the valence electron concentration and average Pauling electronegativity (χp) of the alloys. However, no correlation was observed between the atomic size mismatch, δ, and any investigated hydrogen sorption property such as the maximum storage capacity or onset temperature for hydrogen release.

Application of Intermetallics (La,Ce)Ni5 in Hydrogen Energy Storage Systems

The hydrogen sorption characteristics of La1–xCexNi5 alloys (x = 0, 0.1, 0.2, 0.25, 0.5) were studied in the temperature range 298–363 K. The optimal compositions of intermetallic compounds were determined for use as hydrogen sorbents in reusable accumulators: compounds La0.9Ce0.1Ni5 and La0.8Ce0.2Ni5. Based on them, a metal hydride hydrogen accumulator was designed and manufactured and its technical and operational characteristics were found. The developed devices are proposed to be applied in electric energy storage systems using hydrogen as an energy carrier.

Reversible Hydrogen Storage Using Nanocomposites

In the field of energy storage, recently investigated nanocomposites show promise in terms of high hydrogen uptake and release with enhancement in the reaction kinetics. Among several, carbonaceous nanovariants like carbon nanotubes (CNTs), fullerenes, and graphitic nanofibers reveal reversible hydrogen sorption characteristics at 77 K, due to their van der Waals interaction. The spillover mechanism combining Pd nanoparticles on the host metal-organic framework (MOF) show room temperature uptake of hydrogen. Metal or complex hydrides either in the nanocomposite form and its subset, nanocatalyst dispersed alloy phases illustrate the concept of nanoengineering and nanoconfinement of particles with tailor-made properties for reversible hydrogen storage. Another class of materials comprising polymeric nanostructures such as conducting polyaniline and their functionalized nanocomposites are versatile hydrogen storage materials because of their unique size, high specific surface-area, pore-volume, and bulk properties. The salient features of nanocomposite materials for reversible hydrogen storage are reviewed and discussed.

Specific features of the formation, catalytic activity, and corrosion stability of PdCu electrolytic co-deposit

A mixed electrolytic deposit (ED) of PdCu (~20 at.% Cu) is synthesized from a solution of 1 mМ PdSO4 + 5 mМ CuSO4 + 0.5 M H2SO4 in the region of copper underpotential deposition (+400 mV vs. RHE). The incorporation of copper into the Pd deposit increases its true surface area (Strue) by a factor of ~20 and changes its hydrogen sorption characteristics. The ED PdCu demonstrates higher specific activity in FAOR as compared with individual Pd deposit (Еdep = 0.4 V). The specific solubility of Pd from ED PdCu is shown to be 2–3 times lower than the solubility of ED Pd; however, its total solubility from PdCu increases due to the strong increase in Strue.

Multiple improvements of hydrogen sorption and their mechanism for MgH2 catalyzed through TiH2@Gr

The present investigation reports the effect of TiH2 templated over graphene (TiH2@Gr) on the hydrogen sorption characteristics of MgH2/Mg. The as synthesized TiH2@Gr leads to significant effect on sorption in MgH2 by the following effects: the first is dehydrogenation of MgH2–TiH2@Gr, which leads to the conversion of some part of TiH2 into TiH1.924. TiH2 together with TiH1.924 works as a better catalyst than TiH2 alone. The second is ball-milling of TiH2@Gr, which produces defective graphene, which also works as co-catalyst. The third is anchoring of TiH2 on graphene, which does not allow the catalyst to agglomerate. The catalytic effect of TiH2@Gr on MgH2 is found to be better than Ti@Gr and TiO2@Gr. The onset desorption temperature for MgH2–TiH2@Gr is ~204 °C, which is 31 °C and 36 °C lower than MgH2–Ti@Gr, MgH2–TiO2@Gr respectively. The better catalytic behavior of TiH2@Gr also persists during de/re-hydrogenation kinetics and cycling study of MgH2. The feasible mechanism for superior catalytic for TiH2@Gr on MgH2 has been put forward.

Investigation of Hydrogen Storage Characteristics of MgH2 Based Materials with Addition of Ni and Activated Carbon

Magnesium-based materials are promising as hydrogen storage media due to their high theoretical hydrogen absorption capacity, abundance and low price. The subject of this study are the hydrogen sorption characteristics of the composites 80 wt % MgH2-15 wt % Ni-5 wt % activated carbon (synthesized from polyolefin wax, a waste product of polyethylene production at low pressure which will be denoted further in the text as POW) and 90 wt % MgH2-5 wt % Ni-5 wt % POW, prepared by ball milling under argon atmosphere. Structure, phase and surface composition of the samples before and after hydrogenation are determined by XRD and TEM. The maximum absorption capacity value of the composites at a temperature 573 K and after 60 min. of hydrogenation are 5.3 wt % H2 for the material with higher Ni content and 5.5 wt % H2 for the other sample. The presence of both additives—nickel and activated carbon derived from POW—has a positive impact on hydrogenation kinetics and the capacity achieved. The results from TEM characterization, e.g., the polycrystalline SAED (selected area electron diffraction) show the presence of graphite, Mg and monoclinic Mg2NiH4.

Effect of ammonia and boron modifications on the surface and hydrogen sorption characteristics of activated carbons from coal

In this study, a synthesis procedure was adopted to prepare boron following nitrogen modified activated carbons from coals collected from Kilimli Zonguldak in Turkey. The effects of ammonia and boron modification on the surface and hydrogen sorption characteristics of these coal based activated carbons were investigated. The modification process was carried out by treatment of potassium hydroxide modified activated carbons with ammonia solution, followed by borax decahydrate solutions at various concentrations (0.025–0.1 M). The porous structure of the samples was characterized by using N2 adsorption-desorption data measured at 77.4 K for the relative pressures in the range P/P0 = 0–1. The resulting samples were in irregular structures having high microporosity. The surface area of the sample characterized by the Brunauer-Emmett-Teller model, having a value of 2195 m2/g by ammonia treatment, increased to 3037 and 2661 m2/g after treatments with the 0.075 M and 0.1 M borax decahydrate solutions, respectively. Hydrogen uptake capacities in the range 2.77–4.14 % wt were obtained by borax decahydrate treatments of the ammonia modified samples, whereas the ammonia treated sample had a capacity of 2.35 % wt before boron modifications. 0.075 M borax decahydrate-ammonia treated sample had the highest surface area and total pore volumes among all the other samples obtained. Increasing borax decahydrate concentration in the range 0.025–0.075 M resulted in the increase of hydrogen uptake capacities due to the improvement in surface characteristics including microporous structure and the affinities of nitrogen and boron to hydrogen. The process adopted for boron modification followed by ammonia treatment of the potassium hydroxide activated coal-based carbons yielded improved surface and hydrogen sorption characteristics as compared to the unmodified carbons.

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.

A dual borohydride (Li and Na borohydride) catalyst/additive together with intermetallic FeTi for the optimization of the hydrogen sorption characteristics of Mg(NH2)2/2LiH.

The present study deals with the material tailoring of Mg(NH2)2-2LiH through dual borohydrides: the reactive LiBH4 and the non-reactive NaBH4. Furthermore, a pulverizer, as well as a catalyst FeTi, has been added in order to facilitate hydrogen sorption. Addition of LiBH4 to LiNH2 in a 1 : 3 molar ratio leads to the formation of Li4(BH4)(NH2)3 which also acts as a catalyst. However, the addition of NaBH4 doesn't lead to any compound formation but shows a catalytic effect. The onset dehydrogenation temperature of thermally treated Mg(NH2)2-2LiH/(Li4(BH4)(NH2)3-NaBH4) is 142 °C as against 196 °C for the basic material Mg(NH2)2-2LiH. However, with the FeTi catalyzed Mg(NH2)2-2LiH/(Li4(BH4)(NH2)3-NaBH4, it has been reduced to 120 °C. This is better than other similar amide/hydride composites where it is 149 °C (when the basic material is catalyzed with LiBH4). The FeTi catalyzed Mg(NH2)2-2LiH/(Li4(BH4)(NH2)3-NaBH4 sample shows better de/re-hydrogenation kinetics as it desorbs 3.9 ± 0.04 wt% and absorbs nearly 4.1 ± 0.04 wt% both within 30 min at 170 °C (with the H2 pressure being 0.1 MPa for desorption and 7 MPa for absorption). The eventual hydrogen storage capacity of Mg(NH2)2-2LiH/(Li4(BH4)(NH2)3-NaBH4 together with FeTi has been found to be ∼5.0 wt%. To make the effect of catalysts intelligible, we have put forward in a schematic way the role of Li and Na borohydrides with FeTi for improving the hydrogen sorption properties of Mg(NH2)2-2LiH.

Hydrogen Sorption Characteristics of Ordered Mesoporous Carbons: Experimental and Modeling View Point

Ordered mesoporous carbons NCCR-41, NCCR-56, CMK-3, CMK-1, NCCR-11, and CMK-8 with varying pore size and pore dimensionality are prepared by adopting a nanocasting method employing sucrose as a car...

Anomalous H2 Desorption Rate of NaAlH4 Confined in Nitrogen-Doped Nanoporous Carbon Frameworks

Confining NaAlH4 in nanoporous carbon scaffolds is known to alter the sorption kinetics and/or pathways of the characteristic bulk hydride reactions through interaction with the framework at the interface, increased specific surface area of the resulting nanoparticles, decreased hydrogen diffusion distances, and prevention of phase segregation. Although the nanosize effects have been well studied, the influence of the carbon scaffold surface chemistry remains unclear. Here we compare the hydrogen sorption characteristics of NaAlH4 confined by melt infiltration in nitrogen-doped/undoped ordered nanoporous carbon of two different geometries. 23Na and 27Al MAS NMR, N2 sorption, and PXRD verify NaAlH4 was successfully confined and remains intact in the carbon nanopores after infiltration. Both the N-doped/undoped nanoconfined systems demonstrate improved reversibility in relation to the bulk hydride during hydrogen desorption/absorption cycling. Isothermal kinetic measurements indicate a lowering of the activ...

Hydrogen Sorption Characteristics of ZrCrAl Ternary Alloy as a Function of Milling Time

Intermetallic compounds which absorb large quantities of hydrogen have received considerable attention recently. The AB2 laves phase intermetallic compound is known to be a potential material for hydrogen storage, owing to its large storage capacity, ease of activation and rapid reaction rate with hydrogen. In this work Al has been chosen as a substitute material for Cr and ZrCrAl ternary alloy is prepared using arc furnace. The mechanical alloying process has been introduced to produce nanocrystalline material. This paper presents comprehensive study on structural aspects of ball milled ZrCrAl alloy. On comparison of the XRD data, the broadening was found in the peak width with the increase of milling time which is clear indication of refinement of crystallite size. This refinement could also be confirmed from the SEM analysis also. PCT measurements were performed for a temperature range 303 K–373 K.

Synthesis and characterization of KOH/boron modified activated carbons from coal and their hydrogen sorption characteristics

Activated carbons from bituminous coal taken from the area of Zonguldak Kilimli region in Turkey were synthesized by chemical activation using a mixed combination of KOH and as a boron source borax decahydrate. The modification process consists of chemical activation of the demineralized coal with KOH (KOH/coal:4/1) and various concentrations of borax decahydrate solutions (0.025–0.1 M). Textural properties such as surface area and pore structure were studied by volumetric methods using N2 adsorption data at 77.4 K (P/P0 = 0–1). The samples obtained have high microporosity, in the form of irregular structures. The EDAX spectra indicate that Boron heteroatoms are attached to surface of AC41, and as BDH concentration increases from 0.025 M to 0.1 M, higher atomic percent of boron is accumulated at the surfaces. AC41 exhibits amorphous structures, whereas BDH modified AC41 consists of predominantly amorphous structure and disordered graphitic carbon. Among the synthesized boron modified samples, the highest surface area, total pore volume and average pore diameters were found for the 0.025 M_BDH-AC41 sample. As the BDH concentration increases, the volume of N2 adsorbed decreases. Surface area of CC and AC41 samples were 52.62 and 2228 m2/g, respectively, whereas surface area of the boron modified samples were found in the range of 2190–2704 m2/g. Hydrogen sorption capacities of the KOH/boron modified samples were found in the range between 2.08 and 3.74% wt. Hydrogen sorption capacity of AC41 obtained was 4.11% wt. Increasing boron concentration resulted in the decrease of hydrogen sorption capacities. Boron modified activated carbons were prepared successfully from coal samples by chemical activation using a mixed combination of KOH and BDH.

Self-assembled air-stable magnesium hydride embedded in 3-D activated carbon for reversible hydrogen storage.

The rational design of stable, inexpensive catalysts with excellent hydrogen dynamics and sorption characteristics under realistic environments for reversible hydrogen storage remains a great challenge. Here, we present a simple and scalable strategy to fabricate a monodispersed, air-stable, magnesium hydride embedded in three-dimensional activated carbon with periodic synchronization of transition metals (MHCH). The high surface area, homogeneous distribution of MgH2 nanoparticles, excellent thermal stability, high energy density, steric confinement by carbon, and robust architecture of the catalyst resulted in a noticeable enhancement of the hydrogen storage performance. The resulting MHCH-5 exhibited outstanding hydrogen storage performance, better than that of most reported Mg-based hydrides, with a high storage density of 6.63 wt% H2, a rapid kinetics loading in <5 min at 180 °C, superior reversibility, and excellent long-term cycling stability over ∼435 h. The significant reduction of the enthalpy and activation energy observed in the MHCH-5 demonstrated enhancement of the kinetics of de-/hydrogenation compared to that of commercial MgH2. The origin of the intrinsic hydrogen thermodynamics was elucidated via solid state 1H NMR. This work presents a readily scaled-up strategy towards the design of realistic catalysts with superior functionality and stability for applications in reversible hydrogen storage, lithium ion batteries, and fuel cells.