Effects of highly dispersed Ni nanoparticles on the hydrogen storage performance of MgH_(2)

MgH_(2)with a large hydrogen capacity is regarded as a promising hydrogen storage material.However,it still suffers from high thermal stability and sluggish kinetics.In this paper,highly dispersed nano-Ni has been successfully prepared by using the polyol reduction method with an average size of 2.14 nm,which significantly improves the de/rehydrogenation properties of MgH_(2).The MgH_(2)–10wt%nano-Ni sample starts releasing H_(2)at 497 K,and roughly 6.2wt%H_(2)has been liberated at 583 K.The rehydrogenation kinetics of the sample are also greatly improved,and the adsorption capacity reaches 5.3wt%H_(2)in 1000 s at 482 K and under 3 MPa hydrogen pressure.Moreover,the activation energies of de/rehydrogenation of the MgH_(2)–10wt%nano-Ni sample are reduced to(88±2)and(87±1)kJ·mol−1,respectively.In addition,the thermal stability of the MgH_(2)–10wt%nano-Ni system is reduced by 5.5 kJ per mol H_(2)from that of pristine MgH_(2).This finding indicates that nano-Ni significantly improves both the thermodynamic and kinetic performances of the de/rehydrogenation of MgH_(2),serving as a bi-functional additive of both reagent and catalyst.

Catalytic effect of Ni@rGO on the hydrogen storage properties of MgH2

Uniform-uispersed Ni nanoparticics(NPs)anchored on reduced graphene oxide(Ni@rGO)catalyzed MgH2(MH-Ni@rGO)has been fabricated by mechanical milling.The effects of milling time and Ni loading amount on the hydrogen storage properties of MgH2 have been investigated.The initial hydrogen desorption temperature of MgH2 catalyzed by 10 wt.%Ni4@rGO6 for milling 5 h is significantly decreased from 251℃ to 190℃.The composite can absorb 5.0 wt.%hydrogen in 20 min at 100℃,while it can desorb 6.1 wt.%within 15 min at 300℃.Through the investigation of the phase transformation and dehydrogenation kinetics during hydrogen ab/desorption cycles,we found that the in-situ formed Mg2Ni/Mg2NiH4 exhibited better catalytic effect than Ni.When Ni loading amount is 45 wt.%,the rGO in Ni@rGO catalysts can prevent the reaction of Ni and Mg due to the strong interaction between rGO and Ni NPs.

Effects of Fe Modified Na2WO4 Additive on the Hydrogen Storage Properties of MgH2

A Fe modified Na2WO4 compound was synthesized by a solution impregnation method and was ball-milled with MgH2 to constitute a novel MgH2-Fe2O3/Na2WO4 composite. The effects of the Fe2O3/Na2WO4 additive on the hydrogen storage properties of MgH2 together with the corresponding mechanism were investigated. At 423 K, within the first 200 seconds, the hydrogen absorption amount of MgH2+20 wt% Fe2O3/Na2WO4 was almost 5 times that of pure MgH2. And at 573 K, its total hydrogen desorption amount was 7 times that for pure MgH2. Meanwhile, its onset dehydrogenation temperature was 110 K lower than that of pure MgH2. It was worth noting that the MgH2+20 wt% Fe/Na2WO4 presented the lower dehydrogenation reaction activation energy(Ea) of 35.9 kJ·mol^-1 compared to that of pure MgH2. The active MgWO4, Mg2 FeH6 and MgO formed during the milling process were responsible for the improvement of the hydrogen storage properties for MgH2.

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 MgH_(2) through high-energy ball milling.The initial dehydrogenation temperatures of MgH_(2)/Ni−25%X composites are all decreased by about 90℃relative to the as-milled pristine MgH_(2).The Ni−25%Co solid solution exhibits the most excellent catalytic effect,and the milled MgH_(2)/Ni−25%Co composite can release 5.19 wt.%hydrogen within 10 min at 300℃,while the as-milled pristine MgH_(2) can only release 1.78 wt.%hydrogen.More importantly,the dehydrogenated MgH_(2)/Ni−25%Co composite can absorb 5.39 wt.%hydrogen at 275℃within 3 min.The superior hydrogen sorption kinetics of MgH_(2)/Ni−25%Co can be ascribed to the actual catalytic effect of in-situ formed Mg_(2)Ni(Co)compounds.First-principles calculations show that the hydrogen absorption/desorption energy barriers of Mg/MgH_(2) systems decrease significantly after doping with transition metal atoms,which interprets well the improved hydrogen sorption properties of MgH_(2) catalyzed by Ni-based solid solutions.

LiBH4 for hydrogen storage-New perspectives

Hydrogen energy has been recognized as“Ultimate Power Source”in the 21st century.It is a boon in these days of energy crunches and concerns about climate change because of the characterized advantages,such as high energy density,large calorific value,abundant resource,zero pollution,zero carbon emission,storable and renewable.State-of-the-art perspectives on tuning the stable thermodynamics and sluggish kinetics of dehydrogenation and re-hydrogenation of LiBH4,which has been regarded as a promising hydrogen storage alternative for onboard energy carrier applications have been discussed.Five major technological approaches are involved,including nanoengineering,catalyst modification,ions substitution,reactant destabilization and a novel process termed as high-energy ball milling with in-situ aerosol spraying(BMAS).It is worth noting that BMAS has the potential to help overcome the kinetic barriers for thermodynamically favorable systems like LiBH4 t MgH2 mixture and provide thermodynamic driving force to enhance hydrogen release at a lower temperature.

Hydrogenation/Dehydrogenation Performances of the MgH_2-WS_2 Composites

The hydrogenation/dehydrogenation kinetics and thermodynamic behaviors of the MgH2- WS2 composites were investigated. The TPD （Temperature-Programmed-Desorption） curves showed that the onset dehydrogenation temperature of the MgH2 ＋ 20wt% WS2 composite was 615 K, 58 K lower than that of the pristine MgH2. The kinetic measurements showed that within 21 rain, the MgH2 ＋ 20wt% WS2 composite could absorb 2.818wt% at 423 K, and release 4.244 wt% of hydrogen at 623 K, while the hydriding/ dehydriding capacity of MgH2 reached only 0.979wt% and 2.319wt% respectively under identical conditions. The improvement of hydrogenation/dehydrogenation performances for the composite was attributed to the co- catalytic effect between the new phases W and MgS which formed durin~ the ball-milliw, ~rocess.

First-Principles Study of Pd Single-Atom Catalysis to Hydrogen Desorption Reactions on MgH2（110） Surface

MgH2 is a promising and popular hydrogen storage material.In this work,the hydrogen desorption reactions of a single Pd atom adsorbed MgH2(110)surface are investigated by using first-principles density functional theory calculations.We find that a single Pd atom adsorbed on the MgH2(110)surface can significantly lower the energy barrier of the hydrogen desorption reactions from 1.802 eV for pure MgH2(110)surface to 1.154 eV for Pd adsorbed MgH2(110)surface,indicating a strong Pd single-atom catalytic effect on the hydrogen desorption reactions.Furthermore,the Pd single-atom catalysis significantly reduces the hydrogen desorption temperature from 573K to 367K,which makes the hydrogen desorption reactions occur more easily and quickly on the MgH2(110)surface.We also discuss the microscopic process of the hydrogen desorption reactions through the reverse process of hydrogen spillover mechanism on the MgH2(110)surface.This study shows that Pd/MgH2 thin films can be used as good hydrogen storage materials in future experiments.

机械合金化法制备非晶Nb60TM40-MgH2(TM=Ni,Fe)复合储氢材料的吸放氢性能

采用机械合金化法制备了Nb60Ni40及Nb60Fe40非晶合金,再通过球磨法向MgH2中分别掺杂10%上述非晶,并利用XRD、SEM、P-C-T、DSC等分析测试手段对样品的微观结构及吸放氢性能进行了表征。XRD结果表明,通过机械合金化法得到了Nb-Ni和Nb-Fe非晶。SEM观察显示,掺杂非晶后,MgH2粉末颗粒得到了细化。P-C-T测试结果表明,非晶Nb60Ni40及Nb60Fe40的掺杂未改善MgH2的吸放氢热力学性能,但非晶Nb60Ni40-MgH2及非晶Nb60Fe40-MgH2复合粉体的吸氢速率有一定的提升;放氢动力学测试表明,非晶掺杂加快了MgH2的放氢速率,350℃下10min即可实现完全放氢。DSC测试结果显示,非晶Nb60Ni40-MgH2体系和非晶Nb60Fe40-MgH2体系的放氢激活能分别为146.14和145.65kJ/mol,与纯MgH2相比分别降低了22.68和23.17kJ/mol。

Robust architecture of 2D nano Mg-based borohydride on graphene with superior reversible hydrogen storage performance

Efficient technical strategies to synthesize hydrides with high capacity and favorable reversibility are significant for the development of novel energy materials.Herein,nano Mg-based borohydride,Mg(BH_(4))_(2),with robust architecture was designed and prepared by confining on graphene through a solution selfconfinement method.The Mg(BH_(4))_(2) confined on graphene displays a wrinkled 2D nano layer morphology within 8.8 nm thickness.Such 2D nano Mg(BH_(4))_(2) can start dehydrogenation at 67.9℃ with a high capacity of 12.0 wt.%,which is 190.5℃ lower than pristine Mg(BH_(4))_(2).The isothermal dehydrogenation tests and kinetics fitting results indicate the 2D nano Mg(BH_(4))_(2) possesses much-enhanced dehydrogenation kinetics of 31.3 kJ/mol activation energy,which is only half of pristine Mg(BH_(4))_(2).The thermodynamics of the 2D nano Mg(BH_(4))_(2) is also verified by PCT tests,of which Gibbs free energy value for the confined 2D nano Mg(BH_(4))_(2) is estimated to be-18.01 kJ/mol H_(2),lower than-16.36 kJ/mol H_(2) of pristine Mg(BH_(4))_(2).Importantly,the reversibility of the confined 2D nano Mg(BH_(4))_(2) is significantly enhanced to over 90%capacity retention with relatively kinetics stability during 10 cycles.The mechanism analyses manifest that Mg(BH_(4))_(2) exhibits stable 2D nano morphology during 10 cyclic tests,resulting in the greatly reduced H diffusion path and the improved de/rehydrogenation kinetics of the 2D nano Mg(BH_(4))_(2).Based on theoretical calculations of Mg(BH_(4))_(2) and the intermediate MgB12H12 confined on graphene,the charge transfer status of both samples is modified to facilitate de/rehydrogenation,thus leading to the significant thermodynamic improvements of the reversible hydrogen storage performances for 2D nano Mg(BH_(4))_(2).Such investigation of the Mg-based borohydride will illuminate prospective technical research of energy storage materials.

Realizing nano-confinement of magnesium for hydrogen storage using vapour transport deposition

A new approach was developed to successfully load Mg into the nanometre-sized pores of an anodic aluminium oxide（AAO） template for realizing the nano-confinement of Mg. Structural characterization shows that Mg nano-particles are nucleated along the AAO pipe wall together with the formation of MgO and Mg17Al12 as byproducts. The flow rate of argon gas, the temperature of the AAO template and the transporting distance between the Mg vapour source and the AAO template were optimized to achieve the confinement of Mg nano-particles with larger loading rate. Under optimized deposition conditions, the particle size of the loaded Mg is less than 100 nm and the effective filling factor is about 35 wt%. The confined Mg/MgH2 even after 10 de-/hydrogenation cycles still shows favourable kinetics. Furthermore, the slight reduction in hydrogen desorption enthalpy and entropy of MgH2 from（74.42 ± 0.12） to（73.21 ± 0.04） k J·mol^-1 and（130.98 ±0.05） to（130.11 ± 0.24） Jámol^-1·K^-1 is also found in the present nano-confinement.