Study on catalytic effect and mechanism of MOF (MOF = ZIF-8, ZIF-67, MOF-74) on hydrogen storage properties of magnesium

Using a deposition-reduction method, Mg/MOF nanocomposites were prepared as composites of Mg and metal-organic framework materials (MOFs = ZIF-8, ZIF-67 and MOF-74). The addition of MOFs can enhance the hydrogen storage properties of Mg. For example, within 5000 s, 0.6 wt%, 1.2 wt%, 2.7 wt%, 3.7 wt% of hydrogen were released from Mg, Mg/MOF-74, Mg/ZIF-8, Mg/ZIF-67, respectively. Activation energy values of 198.9 kJ mol⁻¹ H₂, 161.7 kJ mol⁻¹ H₂, 192.1 kJ mol⁻¹ H₂ were determined for the Mg/ZIF-8, Mg/ZIF-67, Mg/MOF-74 hydrides, which are 6 kJ mol⁻¹ H₂, 43.2 kJ mol⁻¹ H₂, and 12.8 kJ mol⁻¹ H₂ lower than that of Mg hydride, respectively. Moreover, the cyclic stability characterizing Mg hydride was significantly improved when adding ZIF-67. The hydrogen storage capacity of the Mg/ZIF-67 nanocomposite remained unchanged, even after 100 cycles of hydrogenation/dehydrogenation. This excellent cyclic stability may have resulted from the core-shell structure of the Mg/ZIF-67 nanocomposite.     

Synergistic catalytic effects of ZIF-67 and transition metals (Ni,Cu, Pd,and Nb) on hydrogen storage properties of magnesium

MgTM/ZIF-67 nanocomposites were prepared by the deposition-reduction method using ZIF-67, MgCl₂, and TMCl_x (TM = Ni, Cu, Pd, Nb) as raw materials. The dehydrogenation activation energies of MgTM/ZIF-67 (TM = Ni, Cu, Pd, Nb) nanocomposites were calculated to be 115.4 kJ mol⁻¹ H₂, 115.7 kJ mol⁻¹ H₂, 113.6 kJ mol⁻¹ H₂, and 75.8 kJ mol⁻¹ H₂, respectively; hence, the MgNb/ZIF-67 nanocomposite manifested the best comprehensive hydrogen storage performance. The hydrogen storage capacity of the MgNb/ZIF-67 nanocomposite was hardly attenuated after the 100th hydrogen absorption-desorption cycle. The dehydrogenated enthalpies of MgH₂ and CoMg₂H₅ in MgNb/ZIF-67 hydride were calculated to be 72.4 kJ mol⁻¹ H₂ and 81.0 kJ mol⁻¹ H₂, respectively, which were lower than those of additive-free MgH₂ and Mg/ZIF-67. The improved hydrogen storage properties of MgNb/ZIF-67 can be ascribed to the CoMg₂–Mg(Nb) core-shell structure and the catalytic effects of NbH and niobium oxide nanocrystals.     

Theoretical prediction and experimental study on catalytic mechanism of incorporated Ni for hydrogen absorption of Mg

Transition metals, including Ni, show good catalytic activity in the hydrogen storage reaction of Mg. In the present paper, first-principles calculation is performed to predict and analyze the hydriding reaction of Ni-incorporated Mg and experimental study is used to verify the accuracy of the forecast. Theoretical studies show that the hydriding reaction of Ni-incorporated Mg is a diffusion-controlled process. With Ni incorporation, the energy barrier of H₂ dissociation is significantly decreased and the diffusion becomes the limiting step. Experimental studies confirm the results of theoretical studies. Besides, the material with Ni incorporation shows excellent activation performance and rapid absorption rates, leading to a high hydrogen content of 4.1 wt% in 60 s under 240 °C 3.0 MPa H₂ and a low activation energy of 56.1 kJ mol⁻¹ versus 0.4 wt% and 73.5 kJ mol⁻¹ for the material without Ni incorporation. Atomic Ni only plays a role of catalyst.     

Effect of in-situ formed Mg2Ni/Mg2NiH4 compounds on hydrogen storage performance of MgH2

Magnesium-based hydrogen storage materials (MgH₂) are promising hydrogen carrier due to the high gravimetric hydrogen density; however, the undesirable thermodynamic stability and slow kinetics restrict its utilization. In this work, we assist the de/hydrogenation of MgH₂ via in situ formed additives from the conversion of an MgNi₂ alloy upon de/hydrogenation. The MgH₂–16.7 wt%MgNi₂ composite was synthesized by ball milling of Mg powder and MgNi₂ alloy followed by a hydrogen combustion synthesis method, where most of the Mg converted to MgH₂, and the others reacted with the MgNi₂ generating Mg₂NiH₄, which produced in situ Mg₂Ni during dehydrogenation. Results showed that the Mg₂Ni and Mg₂NiH₄ could induce hydrogen absorption and desorption of the MgH₂, that it absorbed 2.5 wt% H₂ at 473 K, much higher than that of pure Mg, and the dehydrogenation capacity increased by 2.6 wt% at 573 K. Besides, the initial dehydrogenation temperature of the composite under the promotion of Mg₂NiH₄ decreased greatly by 100 K, whereas it is 623 K for MgH₂. Furthermore, benefiting from the catalyst effect of Mg₂NiH₄ during dehydrogenation, the apparent activation energy of the composite reduced to 73.2 kJ mol⁻¹ H₂ from 129.5 kJ mol⁻¹ H₂.     

Effects of trimesic acid-Ni based metal organic framework on the hydrogen sorption performances of MgH2

A metal-organic framework based on Ni (II) as metal ion and trimasic acid (TMA) as organic linker was synthesized and introduced into MgH₂ to prepare a Mg-(TMA-Ni MOF)-H composite through ball-milling. The microstructures, phase changes and hydrogen storage behaviors of the composite were systematically studied. It can be found that Ni ion in TMA-Ni MOF is attracted by Mg to form nano-sized Mg₂Ni/Mg₂NiH₄ after de/rehydrogenation. The hydriding and dehydriding enthalpies of the Mg-MOF-H composite are evaluated to be −74.3 and 78.7 kJ mol⁻¹ H₂, respectively, which means that the thermodynamics of Mg remains unchanged. The absorption kinetics of the Mg-MOF-H composite is improved by showing an activation energy of 51.2 kJ mol⁻¹ H₂. The onset desorption temperature of the composite is 167.8 K lower than that of the pure MgH₂ at the heating rate of 10 K/min. Such a significant enhancement on the sorption kinetic properties of the composite is attributed to the catalytic effects of the nanoscale Mg₂Ni/Mg₂NiH₄ derived from TMA-Ni MOF by providing gateways for hydrogen diffusion during re/dehydrogenation processes.     

Improvement of desorption performance of Mg(BH4)2 by two-dimensional Ti3C2 MXene addition

Magnesium borohydride (Mg(BH₄)₂) is an attractive materials for solid-state hydrogen storage due to its high hydrogen content (14.9 wt%). In the present work, the dehydrogenation performance of Mg(BH₄)₂ by adding different amounts (10, 20, 40, 60 wt%) of two-dimensional layered Ti₃C₂ MXene is studied. The Mg(BH₄)₂-40 wt% Ti₃C₂ composite releases 7.5 wt% hydrogen at 260 °C, whereas the pristine Mg(BH₄)₂ only releases 2.9 wt% hydrogen under identical conditions, and the onset desorption temperature decreases from 210 °C to a relative lower temperature of 82 °C. The special layered structure of Ti₃C₂ MXene and fluorine plays an important role in dehydrogenation process especially at temperatures below 200 °C. The main dehydrogenation reaction is divided into two steps, and activation energy of the Mg(BH₄)₂-40 wt% Ti₃C₂ composite is 151.3 kJ mol⁻¹ and 178.0 kJ mol⁻¹, respectively, which is much lower than that of pure Mg(BH₄)₂.     

Microstructural characteristics and hydrogen storage properties of the Mg–Ni–TiS2 nanocomposite prepared by a solution-based method

Magnesium hydride is considered as a promising solid-state hydrogen storage material due to its high hydrogen capacity. How to improve hydrogen desorption kinetics of MgH₂ is one of key issues for its practical applications. In this study, we synthesize a Mg–Ni–TiS₂ composite through a solution-based synthetic strategy. In the as-prepared composite, the co-precipitated Mg and Ni nanoparticles are highly dispersed on TiS₂ nanosheets. As a result, the activation energy for hydrogen desorption decreases to 79.4 kJ mol⁻¹. Meanwhile, the capacity retention rate is kept at the level of 98% and only slight kinetic deterioration is caused after fifty hydrogenation-dehydrogenation cycles. Further investigation indicates that the superior hydrogen desorption kinetics is attributed to the synergistically catalytic effect of the in situ formed Mg₂NiH₄ and TiH₂, and the remained TiS₂. The excellent cycle stability is related not only to the inhibition effect of the secondary phases on powder agglomeration and crystallite growth of Mg and MgH₂ but also to the prevention effect of MgS and TiS₂ on redistribution of catalytic Mg₂NiH₄ and TiH₂ nanoparticles during cycling. This work introduces a feasible approach to develop Mg-based hydrogen storage materials.     

Coupling ultralow-content ruthenium with nickel hydroxide via corrosion engineering for highly efficient hydrogen generation from ammonia borane

Efficient and controllable release of hydrogen from solid hydrogen storage materials is a promising way to produce hydrogen safely and on-demand. The development of economical, highly active, easily recyclable catalysts is critical for practical applications, which remains a great challenging. Herein, the easily controllable and cost-effective corrosion strategy is ingeniously developed to simply prepare ultralow-content ruthenium coupled with nickel hydroxide on nickel foam (Ru–Ni–NF). After experiencing the spontaneous oxidation-reduction reactions between the reactive NF and Ru³⁺, ultrafine Ru nanoparticles decorated nickel hydroxide nanosheets are in situ intimately grown on porous NF networks. The optimal Ru–Ni–NF catalyst exhibits the excellent performance for catalytic hydrolysis of ammonia borane with a high turnover frequency (TOF) of 539.6 mol_H2 mol_Ru^?1 min^?1 at 298 K and a low apparent activation energy of 36.4 kJ mol^?1, due to the synergistic effect between Ru nanoparticles and nickel hydroxide nanosheets. Furthermore, the Ru–Ni–NF catalyst possesses easy separation and outstanding durability, which is superior to powdered catalysts. This study provides a facile and economical strategy for the preparation of ultralow-content noble metal supported metal foam-type catalysts for dehydrogenation of ammonia borane.     

Facile synthesis of nickel-vanadium bimetallic oxide and its catalytic effects on the hydrogen storage properties of magnesium hydride

To improve the dehydrogenation/hydrogenation performance of magnesium hydride (MgH₂), a nickel-vanadium bimetallic oxide (NiV₂O₆) was prepared by a simple hydrothermal method using ammonium metavanadate and nickel nitrate as raw materials. This oxide was used to improve the hydrogen storage performance of MgH₂. NiV₂O₆ reacted with Mg to form Mg₂Ni and V₂O₅; Mg₂Ni and V₂O₅ played an important role in improving the hydrogen storage properties of MgH₂. The NiV₂O₆-doped MgH₂ had an excellent hydrogen absorption and desorption kinetics performance, and it could absorb 5.59 wt% of hydrogen within 50 min at 150 °C and release about 5.3 wt% of hydrogen within 12 min. The apparent activation energies for the dehydrogenation and hydrogenation of MgH₂-NiV₂O₆ were 92.9 kJ mol^?1 and 24.9 kJ mol^?1, respectively. These were 21.7% and 66.3% lower than those of MgH_2, respectively. The mechanism analysis demonstrated that the improved kinetic properties of MgH₂ resulted from the heterogeneous catalysis of vanadium and nickel.     

Precipitation of nanocrystalline LaH3 and Mg2Ni and its effect on de-/hydrogenation thermodynamics of Mg-rich alloys

Based on the catalytic effects of transition metals and rare earth metals on magnesium hydride, precipitation behavior of nanocrystalline LaH₃ and Mg₂Ni has been discussed and correlated with the de-/hydrogenation thermodynamic of Mg-rich alloys in this work. The results show that a significant enhancement of de-/hydrogenation properties has been achieved due to in-situ formed Mg–Mg₂Ni–LaH₃ nanocomposites. It is observed that the Mg₂Ni-rich alloy exhibiting superior performance can desorb about 5.7 wt% hydrogen within 2.5 min at 623 K. The formation of LaH₃ tends to promote the hydrogenation process and the Mg₂Ni is beneficial for improving the dehydrogenation performance. Meanwhile, the phase boundaries between LaH₃, Mg₂Ni and Mg also play positive roles due to stored extra energy on the interface. Fitting kinetics model shows that rate-limiting steps of the as-prepared alloys have changed and the desorption activation energy significantly decreases due to precipitation of nanocrystalline LaH₃ and Mg₂Ni. It is worth noting that desorption activation energy of the preferable composite decreases to 94.03 kJ mol⁻¹. Thermodynamic properties are also investigated and analyzed based on plateau pressure and van't Hoff equation. It is revealed that precipitation of nanocrystalline LaH₃ and Mg₂Ni significantly enhances the hydrogen storage kinetics of Mg-based alloys.     

Iron based catalyst for the improvement of the sorption properties of KSiH3

Recently, silanides (MSiH₃) have been proposed as the possible hydrogen storage materials due to their hydrogen storage properties. Among these silanides, KSiH₃ has been considered as leading contender due to its high hydrogen storage capacity i.e. 4.3 wt% and suitable thermodynamic parameters. It can absorb and desorb hydrogen reversibly at near ambient temperature, however, a high activation barrier slows down its kinetics. To enhance its kinetic properties, several catalysts have been attempted so far. Nb₂O₅ has been proven as leading catalyst with significant improvement. In the present work, Fe based catalysts were chosen due to their suitability for hydrogen storage materials. Among all the studied catalysts in this work, Fe₂O₃ was found to be the most effective catalyst, reducing the activation energy down to 75 kJ mol⁻¹ from 142 kJ mol⁻¹ for pristine KSi.     

Ameliorated microstructure and hydrogen absorption/desorption properties of novel Mg–Ni–La alloy doped with MWCNTs and Co nanoparticles

Based on the positive influence of carbon materials and transition metals, a new type of Mg-based composites with particle size of ～800 nm has been designed by doping hydrogenated Mg–Ni–La alloy with multi-walled carbon nanotubes (MWCNTs) and/or Co nanoparticles. The microstructures, temperature related hydrogen absorption/desorption kinetics and dehydrogenation mechanisms are investigated in detail. The results demonstrate that MWCNTs and Co dispersedly distribute on the surface of Mg–Ni–La particles after high-energy ball milling due to powders’ repeated cold welding and tearing. The experimental samples exhibit improved hydrogen storage behaviors and the addition of MWCNTs and Co can further accelerate the de-/hydriding kinetics. For instance, the Mg–Ni–La–Co sample can absorb 3.63 wt% H₂ within 40 min at 343 K. Dehydrogenation analyses demonstrate that the positive effect of MWCNTs is more obvious than that of Co nanoparticles for the experimental samples. The addition of MWCNTs and Co leads to the average dehydrogenation activation energy of experimental samples decreasing to 82.1 and 84.5 kJ mol^?1, respectively, indicating a significant decrease of dehydrogenation energy barriers. In addition, analyses of dehydrogenation mechanisms indicate that the rate-limiting steps vary with the addition of MWCTNs and Co nanoparticles.     

Improved hydrogen storage properties of Mg-based nanocomposite by addition of LaNi5 nanoparticles

Mg (200 nm) and LaNi₅ (25 nm) nanoparticles were produced by the hydrogen plasma-metal reaction (HPMR) method, respectively. Mg–5 wt.% LaNi₅ nanocomposite was prepared by mixing these nanoparticles ultrasonically. During the hydrogenation/dehydrogenation cycle, Mg–LaNi₅ transformed into Mg–Mg₂Ni–LaH₃ nanocomposite. Mg particles broke into smaller particles of about 80 nm due to the formation of Mg₂Ni. The nanocomposite showed superior hydrogen sorption kinetics. It could absorb 3.5 wt.% H₂ in less than 5 min at 473 K, and the storage capacity was as high as 6.7 wt.% at 673 K. The nanocomposite could release 5.8 wt.% H₂ in less than 10 min at 623 K and 3.0 wt.% H₂ in 16 min at 573 K. The apparent activation energy for hydrogenation was calculated to be 26.3 kJ mol⁻¹. The high sorption kinetics was explained by the nanostructure, catalysis of Mg₂Ni and LaH₃ nanoparticles, and the size reduction effect of Mg₂Ni formation.     

Enhancing hydrogen storage properties of the Mg/MgH2 system by the addition of bis(tricyclohexylphosphine)nickel(II) dichloride

This is a first report on the use of the bis(tricyclohexylphosphine)nickel (II) dichloride complex (abbreviated as NiPCy3) into MgH₂ based hydrogen storage systems. Different composites were prepared by planetary ball-milling by doping MgH₂ with (i) free tricyclohexylphosphine (PCy3) without or with nickel nanoparticles, (ii) different NiPCy3 contents (5–20 wt%) and (iii) nickel and iron nanoparticles with/without NiPCy3. The microstructural characterization of these composites before/after dehydrogenation was performed by TGA, XRD, NMR and SEM-EDX. Their hydrogen absorption/desorption kinetics were measured by TPD, DSC and PCT. All MgH₂ composites showed much better dehydrogenation properties than the pure ball-milled MgH₂. The hydrogen absorption/release kinetics of the Mg/MgH₂ system were significantly enhanced by doping with only 5 wt% of NiPCy3 (0.42 wt% Ni); the mixture desorbed H₂ starting at 220 °C and absorbed 6.2 wt% of H₂ in 5 min at 200 °C under 30 bars of hydrogen. This remarkable storage performance was not preserved upon cycling due to the complex decomposition during the dehydrogenation process. The hydrogen storage properties of NiPCy3-MgH₂ were improved and stabilized by the addition of Ni and Fe nanoparticles. The formed system released hydrogen at temperatures below 200 °C, absorbed 4 wt% of H₂ in less than 5 min at 100 °C, and presented good reversible hydriding/dehydriding cycles. A study of the different storage systems leads to the conclusion that the NiPCy3 complex acts by restricting the crystal size growth of Mg/MgH₂, catalyzing the H₂ release, and homogeneously dispersing nickel over the Mg/MgH₂ surface.     

Low-cost CuFeCo@MIL-101 as an efficient catalyst for catalytic hydrolysis of ammonia borane

Trimetallic nanoparticles of non-noble Cu–Fe–Co with different molar ratios were successfully immobilized in the metal-organic frameworks (MIL-101) via an easy impregnation–reduction process. XRD, TEM, XPS, ICP-MS and BET methods were used to characterize the catalyst. Comparing to their bimetallic counterparts, Cu₆Fe_0.8Co_3.2@MIL-101 demonstrates the best catalytic performance for dehydrogenation of ammonia borane by hydrolysis at 298 K Cu₆Fe_0.8Co_3.2@MIL-101 shows a total turnover frequency (TOF) value of 23.2 mol_H2 mol_catalyst⁻¹ min⁻¹ and an activation energy value of 37.1 kJ mol⁻¹. The enhancement of catalytic activity was attributed to a synergistic effect among copper, cobalt and iron nanoparticles supported on MIL-101. In addition, the catalyst still exhibits good stability and magnetic recyclability after seven cycles. The low-cost catalyst has good prospect for application in the field of hydrogen storage.     

Hydrogen production via copper nanocatalysts stabilized by cyclen derivative hydrogel networks from the hydrolysis of ammonia borane and ethylenediamine bisborane

In this study, p(AAm-co-TACYC) hydrogels were synthesized using TACYC crosslinker. The p(AAm-co-TACYC) hydrogel was used for preparation of Cu(0) nanoparticles as support material. The p(AAm-co-TACYC)@Cu was prepared by chemical reduction of Cu²⁺ ions in the p(AAm-co-TACYC) networks and was structurally characterized in detail. Later the catalytic activity of p(AAm-co-TACYC)@Cu was investigated for hydrogen production from AB and EDAB hydrolysis. Detailed kinetic studies were performed for both hydrogen storage materials. The p(AAm-co-TACYC)@Cu was a more active catalyst for the EDAB hydrolysis reaction. The E_a values of p(AAm-co-TACYC)@Cu for the AB and EDAB hydrolysis reactions were determined as 68.36 kJ mol⁻¹ and 39.07 kJ mol⁻¹, respectively. In addition to the perfect catalytic activity of p(AAm-co-TACYC)@Cu, it had good reusability. After ten consecutive uses for AB and EDAB hydrolysis, the p(AAm-co-TACYC)@Cu still had 88% and 85% of initial activity, respectively.     

Microstructural evolution and hydrogen storage proprieties of melt-spun eutectic Mg76.87Ni12.78Y10.35 alloy with low hydrides formation/decomposition enthalpy

Ternary eutectic Mg_76.87Ni_12.78Y_10.35 (at. %) ribbons with mixed amorphous and nanocrystalline phases were prepared by melt spinning. The microstructures of the melt-spun, hydrogenated and dehydrogenated samples were examined and compared by X-ray diffraction and transmission electron microscopy. The amorphous structure transforms into a thermally stable nanocrystalline structure with a grain size of about 5 nm during hydrogen ab/desorption cycles. The Mg, Mg₂Ni and phases with Y in the melt-spun state transform into MgH₂, Mg₂NiH₄, Mg₂NiH_0.3, YH₂ and YH₃ after hydrogenation, and transform back to Mg, Mg₂Ni and YH₂ upon subsequent dehydrogenation. The reaction enthalpy (ΔH) and entropy (ΔS) of the higher plateau pressure corresponding to Mg₂Ni hydride formation are −53.25 kJ mol⁻¹ and −107.74 J K⁻¹ mol⁻¹, respectively. The amorphous/nanocrystalline structure effectively reduces the enthalpy and entropy of Mg₂Ni hydride formation, but has little effect on Mg. The activation energy for dehydrogenation of the hydrogenated ribbons is 69 kJ mol⁻¹. This suggests that Mg–Ni–Y with ternary eutectic composition can form an amorphous/nanocrystalline structure by melt spinning, and this nanostructure efficiently improves the thermodynamics and kinetics for hydrogen storage.     

Hydrogen adsorption properties of in-situ synthesized Pt-decorated porous carbons templated from zeolite EMC-2

To increase the interaction between the adsorbed hydrogen and the adsorbent surface to improve the hydrogen storage capacity at ambient temperature, decorating the sorbents with metal nanoparticles, such as Pd, Ni, and Pt has attracted the most attention. In this work, Pt-decorated porous carbons were in-situ synthesized via CVD method using Pt-impregnated zeolite EMC-2 as template and their hydrogen uptake performance up to 20 bar at 77, 87, 298 and 308 K has been investigated with focus on the interaction between the adsorbed H₂ and the carbon matrix. It is found that the in-situ generated Pt-decorated porous carbons exhibit Pt nanoparticles with size of 2–4 nm homogenously dispersed in the porous carbon, accompanied with observable carbon nanowires on the surface. The calculated H₂ adsorption heats at/near 77 K are similar for both the plain carbon (7.8 kJ mol⁻¹) and the Pt-decorated carbon (8.3 kJ mol⁻¹) at H₂ coverage of 0.08 wt.%, suggesting physisorption is dominated in both cases. However, the calculated H₂ adsorption heat at/near 298 K of Pt-decorated carbon is 72 kJ mol⁻¹ at initial H₂ coverage (close to 0), which decreases dramatically to 20.8 kJ mol⁻¹ at H₂ coverage of 0.014 wt.%, levels to 17.9 at 0.073 wt.%, then gradually decreases to 2.6 kJ mol⁻¹ at 0.13 wt.% and closes to that of the plain carbon at H₂ coverage above 0.13 wt.%. These results suggest that the introduction of Pt particles significantly enhances the interaction between the adsorbed H₂ and the Pt-decorated carbon matrix at lower H₂ coverage, resulting in an adsorption process consisting of chemisorption stage, mixed nature of chemisorption and physisorption stage along with the increase of H₂ coverage (up to 0.13 wt.%). However, this enhancement in the interaction is outperformed by the added weight of the Pt and the blockage and/or occupation of some pores by the Pt nanoparticles, which results in lower H₂ uptake than that of the plain carbon.     

Hydrogen production from ammonia borane via hydrogel template synthesized Cu, Ni, Co composites

In situ Co, Cu and Ni nanoparticles were synthesized by chemical reduction of the absorbed Co (II), Cu (II) and Ni (II) ions inside hydrogel networks prepared from 2-acrylamido-2-methyl-1-propansulfonic acid (AMPS) and were used as a catalyst system in the generation of hydrogen in hydrolysis of ammonia borane (AB). Several parameters affecting the hydrolysis reaction such as the type of the metal, the amount of catalyst, the initial concentration of AB, and temperature, were investigated. The activation energy values in the hydrolysis reaction of AB solution in the presence p(AMPS)-Co, p(AMPS)-Cu and p(AMPS)-Ni catalyst systems were calculated as E_a = 47.7 kJ mol⁻¹, 48.8 kJ mol⁻¹ and 52.8 kJ mol⁻¹, respectively. Thus, the catalytic activity of the metal nanoparticles prepared inside the same hydrogel matrix was found to be Ni < Cu < Co.     

Boosting low-temperature de/re-hydrogenation performances of MgH2 with Pd-Ni bimetallic nanoparticles supported by mesoporous carbon

Bimetallic Pd-Ni nano-particles supported by a mesoporous carbon material CMK-3 (denoted as Pd₃₀Ni₇₀/CMK-3) were synthesized through solution impregnation and hydrogen reduction methods. Among those hierarchical Ni-Pd nano-particles, majorly large ones (>10 nm) are dispersed over the surface of CMK-3, while a litter small ones (<10 nm) are embedded into the pores. It significantly improves the de/re-hydrogenation performances of MgH₂ at low temperature. The onset desorption temperature of MgH₂-Pd₃₀Ni₇₀/CMK-3 is lowered by 150 K from that of pristine MgH₂ (above 593 K). About 6 wt% hydrogen could be released during its decomposition below 561 K. Noticeably, MgH₂-Pd₃₀Ni₇₀/CMK-3 is capable of releasing 1.3 wt% H₂ even at 373 K. 4 wt% hydrogen can be absorbed at 343 K under a hydrogen pressure of 3 MPa within 18000 s. Activation energy values of both hydrogen decomposition (65.9 kJ mol⁻¹) and absorption (78.9 kJ mol⁻¹) for MgH₂-Pd₃₀Ni₇₀/CMK-3 are greatly improved from those of as-milled MgH₂. Thermal stability of the composite system is remarkably destabilized by 4.3 kJ mol H₂⁻¹ from pristine MgH₂ according to pressure-composition isotherm curves and van't Hoff plots. The enhanced performances can be ascribed to the synergistic effects of both destabilization and catalysis from nano-dispersed Pd and Ni particles, respectively.