Metal organic framework supported niobium pentoxide nanoparticles with exceptional catalytic effect on hydrogen storage behavior of MgH_(2)

Nb_(2)O_(5)nanoparticles with an average particle size of 10 nm supported on a rhombic dodecahedral metal organic framework(MOF)were successfully synthesized by a facile one-pot hydrothermal reaction and subsequent calcination process.Experimental results demonstrated that the prepared catalyst drastically improved the hydrogen storage behavior of MgH_(2).7 wt%Nb_(2)O_(5)@MOF doped MgH_(2)started to desorb hydrogen at 181.9℃and 6.2 wt%hydrogen could be released within 2.6 min and 6.3 min at 275℃and 250℃,respectively.The fully dehydrogenated composite also displayed excellent hydrogenation by decreasing the onset absorption temperature to 25℃and taking up4.9 wt%and 6.5 wt%hydrogen within 6 min at 1750C and 1500C,respectively.Moreover,the corresponding activation energy was calculated to be 75.57±4.16 kJ mol^(-1)for desorption reaction and 51.38±1.09 kJ mol^(-1)for absorption reaction.After 20 cycles,0.5 wt%hydrogen capacity was lost for the MgH_(2)+7 wt%Nb_(2)O_(5)@MOF composite,much lower than 1.5 wt%of the MgH_(2)+7 wt%Nb_(2)O_(5)composite.However,the addition of Nb_(2)O_(5)@MOF had limited effect on reducing the dehydrogenation enthalpy of MgH_(2).Microstructure analysis revealed that Nb_(2)O_(5)particles were uniformly distributed on surface of the MgH_(2)matrix and synergistically improved the hydrogen storage property of MgH_(2)with MOF.

Bullet-like vanadium-based MOFs as a highly active catalyst for promoting the hydrogen storage property in MgH_(2)

The practical application of magnesium hydride(MgH_(2))was seriously limited by its high desorption temperature and slow desorp-tion kinetics.In this study,a bullet-like catalyst based on vanadium related MOFs(MOFs-V)was successfully synthesized and doped with MgH_(2) by ball milling to improve its hydrogen storage performance.Microstructure analysis demonstrated that the as-synthesized MOFs was consisted of V_(2)O_(3) with a bullet-like structure.After adding 7wt%MOFs-V,the initial desorption temperature of MgH_(2) was reduced from 340.0 to 190.6℃.Besides,the MgH_(2)+7wt%MOFs-V composite released 6.4wt%H_(2) within 5 min at 300℃.Hydrogen uptake was started at 60℃under 3200 kPa hydrogen pressure for the 7wt%MOFs-V containing sample.The desorption and absorption apparent activity energies of the MgH_(2)+7wt%MOFs-V composite were calculated to be(98.4±2.9)and(30.3±2.1)kJ·mol^(-1),much lower than(157.5±3.3)and(78.2±3.4)kJ·mol^(−1) for the as-prepared MgH_(2).The MgH_(2)+7wt%MOFs-V composite exhibited superior cyclic property.During the 20 cycles isothermal dehydrogenation and hydrogenation experiments,the hydrogen storage capacity stayed almost unchanged.X-ray diffraction(XRD)and X-ray photoelectron spectrometer(XPS)measurements confirmed the presence of metallic vanadium in the MgH_(2)+7wt%MOFs-V composite,which served as catalytic unit to markedly improve the hydrogen storage properties of Mg/MgH_(2) system.

FeCoNiCrMo high entropy alloy nanosheets catalyzed magnesium hydride for solid-state hydrogen storage

The catalytic effect of FeCoNiCrMo high entropy alloy nanosheets on the hydrogen storage performance of magnesium hydride(MgH_(2))was investigated for the first time in this paper.Experimental results demonstrated that 9wt%FeCoNiCrMo doped MgH_(2)started to dehydrogenate at 200℃and discharged up to 5.89wt%hydrogen within 60 min at 325℃.The fully dehydrogenated composite could absorb3.23wt%hydrogen in 50 min at a temperature as low as 100℃.The calculated de/hydrogenation activation energy values decreased by44.21%/55.22%compared with MgH_(2),respectively.Moreover,the composite’s hydrogen capacity dropped only 0.28wt%after 20 cycles,demonstrating remarkable cycling stability.The microstructure analysis verified that the five elements,Fe,Co,Ni,Cr,and Mo,remained stable in the form of high entropy alloy during the cycling process,and synergistically serving as a catalytic union to boost the de/hydrogenation reactions of MgH_(2).Besides,the FeCoNiCrMo nanosheets had close contact with MgH_(2),providing numerous non-homogeneous activation sites and diffusion channels for the rapid transfer of hydrogen,thus obtaining a superior catalytic effect.

Identification of the starting reaction position in the hydrogenation of (N-ethyl)carbazole over Raney-Ni

Hydrogenation of carbazole and N-ethylcarbazole over Raney-Ni catalyst were realized in the temperature range of 393-503 K. 4[H] adduct dominated the hydrogenation products and the formation of 2[H] adduct was the rate-limiting step during the period, in which the conversion of carbazole was less than 40%. The hydrogenation process followed pseudo-first-order kinetics and the hydrogenation activation energies of carbazole and N-ethylcarbazole were 90 kJ/mol and 115 kJ/mol, respectively. The reaction starting position as well as the pathway of the hydrogenation of （N-ethyl）carbazole were investigated by comparing the kinetic characteristics of hydrogen uptake of carbazole and N- ethylcarbazole. The results showed that the reaction was a stepwise hydrogenation process and the first H_2 was added to the C1 = C10 double bond in the hydrogenation.

Significantly improved hydrogen storage behaviors in MgH_(2) with Nb nanocatalyst

The study explores the excellent modification effect of Nb nanocatalyst prepared via surfactant assisted ball milling technique(SABM)on the hydrogen storage properties of MgH_(2).Optimal catalyst doping concentration was determined by comparing onset decomposition temperature,released hydrogen capacity,and reaction rate for different MgH_(2)-ywt%Nb(y=0,3,5,7,9)composites.The MgH_(2)-5wt%Nb composite started releasing hydrogen at 186.7℃ and a total of 7.0wt%hydrogen was released in the dehydrogenation process.In addition,5wt%Nb doped MgH_(2) also managed to release 4.2wt%H_(2) within 14 min at 250℃ and had the ability to absorb 4.0wt%hydrogen in 30 min at 100℃.Cycling tests revealed that MgH_(2)-5wt%Nb could retain 6.3wt%H_(2) storage capacity(89.2%)after 20 cycles.Dehydrogenation and hydrogenation activation energy values were decreased from 140.51±4.74 and 70.67±2.07 kJ·mol^(−1) to 90.04±2.83 and 53.46±3.33 kJ·mol^(−1) after doping MgH_(2) with Nb,respectively.Microstructure analysis proved that homogeneously distributed NbH acted as active catalytic unit for improving the hydrogen storage performance of MgH_(2).These results indicate SABM can be considered as an option to develop other nanocatalysts for energy related areas.

Boosting the hydrogen storage performance of magnesium hydride with metal organic framework-derived Cobalt@Nickel oxide bimetallic catalyst

In this study,a MOF-derived bimetallic Co@NiO catalyst was synthesized and doped into MgH_(2)to improve the hydrogen desorption and resorption kinetics.The Co@NiO catalyst decreased the onset dehydrogenation temperature of MgH_(2)by 160℃,compared with un-doped MgH_(2).The MgH^(2+)9%(mass)Co@NiO composite released 6.6%(mass)hydrogen in 350 s at 315℃and uptook 5.4%(mass)hydrogen in500 s at 165℃,showing greatly accelerated de/rehydrogenation rates.Besides,the desorption activation energy of MgH^(2+)9%(mass)Co@NiO was decreased to(93.8±8.4)kJ·mol^(-1).Noteworthy,symbiotic Mg_(2)NiH_(4)/Mg_(2)CoH_(5)clusters were in-situ formed from bimetallic precursors and inlaid on MgH_(2)surface,which are considered as"multi-step hydrogen pumps",and provides surface pathways for hydrogen absorption.Meanwhile,the introduced Mg_(2)NiH_(4)/Mg_(2)CoH_(5)interfaces could provide numerous low energy barrier H diffusion channels,therefore accelerating the hydrogen release and uptake.This research proposes new insights to design high-efficiency bimetallic catalyst for MgH_(2)hydrogen storage.

The effect of different Co phase structure(FCC/HCP)on the catalytic action towards the hydrogen storage performance of MgH_(2)

High hydrogen desorption temperature and sluggish reaction kinetics are the major limitations for the practical application of MgH_(2).In this study,Co particles with a face centered cubic(FCC)structure and a hexagonal close packed(HCP)structure were prepared facilely and proved to be good catalysts for magnesium hydride.Co particles with FCC structure presented better catalytic effect on MgH_(2)than that with HCP structure.Both 7%(mass)Co FCC and HCP particle modified MgH_(2)decreased the initial dehydrogenation temperature from 301.3℃ to approximately 195.0℃,but 7%(mass)Co with FCC structure modified MgH_(2)has a faster desorption rate,and around 6.5%(mass)H_(2)was desorbed in 10 min at325℃.Hydrogen uptake was detected at 70℃ under 3.25 MPa hydrogen pressure and 6.0%(mass)H_(2)was recharged in 40 min at 150℃.The hydrogen desorption and absorption activation energy for 7%(mass)FCC Co modified MgH_(2)was significantly decreased to(76.6±8.3)kJ·mol^(-1) and(68.3±6.0)kJ·mol^(-1),respectively.Thermodynamic property was also studied,the plateau pressures of MgH_(2)+7%(mass)FCC Co were determined to be 0.14,0.28,0.53 and 0.98 MPa for 300℃,325℃,350℃ and375℃.The decomposition enthalpy of hydrogen(ΔH)for MgH_(2)+7%(mass)FCC Co was(80.6±0.1)kJ·mol^(-1),5.8 kJ·mol^(-1)lower than that of as-prepared MgH_(2).Moreover,cycling performance for the first20 cycles revealed that the reaction kinetics and capacity of MgH_(2)-FCC Co composite remained almost unchanged.The result of density functional theory calculation demonstrated that cobalt could extract the Mg AH bond and reduced the decompose energy of magnesium hydride.Our paper can be presented as a reference for searching highly effective catalysts for hydrogen storage and other energy-related research fields.

Enhanced hydrogen storage properties of Mg by the synergistic effect of grain refinement and NiTiO_(3)nanoparticles

As a promising hydrogen storage material,the practical application of magnesium is obstructed by the stable thermodynamics and sluggish kinetics.In this paper,three kinds of NiTiO3catalysts with different mole ratio of Ni to Ti were successfully synthesized and doped into nanocrystalline Mg to improve its hydrogen storage properties.Experimental results indicated that all the Mg-NiTiO3composites showed prominent hydrogen storage performance.Especially,the Mg-NiTiO3/TiO2composite could take up hydrogen at room temperature and the apparent activation energy for hydrogen absorption was dramatically decreased from 69.8±1.2(nanocrystalline Mg)k J/mol to 34.2±0.2 k J/mol.In addition,the hydrogenated sample began to release hydrogen at about 193.2℃and eventually desorbed 6.6 wt%H2.The desorption enthalpy of the hydrogenated Mg-NiTiO3-C was estimated to be 78.6±0.8 k J/mol,5.3 k J/mol lower compared to 83.9±0.7 k J/mol of nanocrystalline Mg.Besides,the sample revealed splendid cyclic stability during 20 cycles.No obvious recession occurred in the absorption and desorption kinetics and only 0.3 wt%hydrogen capacity degradation was observed.Further structural analysis demonstrates that nanosizing and catalyst doping led to a synergistic effect on the enhanced hydrogen storage performance of Mg-NiTiO3-C composite,which might serve as a reference for future design of highly effective hydrogen storage materials.

Recent advances of magnesium hydride as an energy storage material

Energy storage is the key for large-scale application of renewable energy,however,massive efficient en-ergy storage is very challenging.Magnesium hydride(MgH_(2))offers a wide range of potential applications as an energy carrier due to its advantages of low cost,abundant supplies,and high energy storage capac-ity.However,the practical application of MgH_(2) for energy storage is still impeded by its sluggish kinetics,poor cycling stability,etc.Herein,we provide an overview of recent advances of MgH_(2) for enhancing the hydrogen storage,lithium-ion storage,and heat storage performances.For hydrogen storage,a particular emphasis was put on altering the kinetics and thermodynamics of MgH_(2) via catalyzing,alloying,nano-sizing,and compositing.Modifications to MgH_(2) as a battery anode material mainly focus on the effect of additives,electrolytes,and structure configurations.Prototype heat storage apparatus was proposed based on MgH_(2) and coupled with other materials or systems to improve the heat storage and economic efficiency.Besides,prospects of MgH_(2) in these fields are discussed.This review would stimulate more insightful and pioneering research for the design and preparation of MgH_(2) with excellent energy storage performances.

Exceptional catalytic effect of novel rGO-supported Ni-Nb nanocomposite on the hydrogen storage properties of MgH_(2)

The design of an excellent active catalyst to improve the sluggish kinetic and thermodynamic properties of magnesium hydride(MgH_(2))remains a great challenge to achieve its practical application.In this study,a novel Ni-Nb/rGO nanocomposite catalyst was successfully prepared by one-spot hydrothermal and sub-sequent calcination methods.The novel Ni-Nb/rGO nanocomposite exhibits an exceptional catalytic effect on improving MgH_(2) sorption properties.Specifically,the onset desorption temperature of MgH_(2)+10 wt%Ni-Nb/rGO composite is reduced to 198℃,much lower than that of undoped MgH_(2)(330℃).In-terestingly,the composite can release 5.0,5.9,and 6.0 wt%H_(2) within 10 min at 245,260,and 275℃,respectively.Furthermore,the dehydrogenated MgH_(2)+10 wt%Ni-Nb/rGO composite starts to absorb hydrogen even at room temperature with approximate 2.75 wt%H_(2) uptake at 75℃under 3 MPa H_(2) pressure within 30 min and exhibits excellent stability by maintaining 6.0 wt%hydrogen content after 20 cycles at 300℃.Chou’s model suggests that the de/hydrogenation kinetics of Ni-Nb/rGO-modified MgH_(2) switches from surface penetration model to diffusion model at lower temperatures.Additionally,the ac-tivation energies(E a)for the de/hydrogenation of MgH_(2)+10 wt%Ni-Nb/rGO are reduced to 57.8 kJ/mol and 33.9 kJ/mol,which are significantly lower than those of undoped MgH_(2).The work demonstrates that the addition of a novel ternary Ni-Nb/rGO catalyst is an effective strategy to not only boost the sorption kinetics of MgH_(2) but also maintain its cycling property.