Influence of temperature, stress, and grain size on behavior of nano-polycrystalline niobium

Atomic simulations are executed to investigate the creep responses of nano-polycrystalline(NC) niobium established by using the Voronoi algorithm. The effects of varying temperature, applied stress, and grain size(GS) on creep properties and mechanisms are investigated. Notably, the occurrence of tertiary creep is exclusively observed under conditions where the applied stress exceeds 4.5 GPa and the temperature is higher than 1100 K. This phenomenon can be attributed to the significant acceleration of grain boundary and lattice diffusion, driven by the elevated temperature and stress levels. It is found that the strain rate increases with both temperature and stress increasing. However, an interesting trend is observed in which the strain rate decreases as the grain size increases. The stress and temperature are crucial parameters governing the creep behavior. As these factors intensify, the creep mechanism undergoes a sequential transformation: initially from lattice diffusion under low stress and temperature conditions to a mixed mode combining grain boundaries(GBs) and lattice diffusion at moderate stress and mid temperature levels, and ultimately leading to the failure of power-law controlled creep behavior, inclusive of grain boundary recrystallization under high stress and temperature conditions. This comprehensive analysis provides in more detail an understanding of the intricate creep behavior of nano-polycrystalline niobium and its dependence on various physical parameters.

Graphene-loaded nickel−vanadium bimetal oxides as hydrogen pumps to boost solid-state hydrogen storage kinetic performance of magnesium hydride

To modify the thermodynamics and kinetic performance of magnesium hydride(MgH_(2))for solid-state hydrogen storage,Ni_(3)V_(2)O_(8)-rGO(rGO represents reduced graphene oxide)and Ni_(3)V_(2)O_(8)nanocomposites were prepared by hydrothermal and subsequent heat treatment.The beginning hydrogen desorption temperature of 7 wt.%Ni_(3)V_(2)O_(8)-rGO modified MgH_(2)was reduced to 208℃,while the additive-free MgH_(2)and 7 wt.%Ni_(3)V_(2)O_(8)doped MgH_(2)appeared to discharge hydrogen at 340 and 226℃,respectively.A charging capacity of about 4.7 wt.%H_(2)for MgH_(2)+7 wt.%Ni_(3)V_(2)O_(8)-rGO was achieved at 125℃ in 10 min,while the dehydrogenated MgH_(2)took 60 min to absorb only 4.6 wt.%H_(2)at 215℃.The microstructure analysis confirmed that the in-situ generated Mg_(2)Ni/Mg_(2)N_(i)H_(4) and metallic V contributed significantly to the enhanced performance of MgH_(2).In addition,the presence of rGO in the MgH_(2)+7 wt.%Ni_(3)V_(2)O_(8)-rGO composite reduced particle aggregation tendency of Mg/MgH_(2),leading to improving the cyclic stability of MgH_(2)during 20 cycles.

Mn nanoparticles enhanced dehydrogenation and hydrogenation kinetics of MgH_(2) for hydrogen storage

Mn nanoparticles(nano-Mn)were successfully synthesized and doped into MgH_(2) to improve its de/hydrogenation properties.Compared with MgH_(2),the onset desorption temperature of 10 wt.%nano-Mn modified MgH_(2) was decreased to 175℃ and 6.7,6.5 and 6.1 wt.%hydrogen could be released within 5,10 and 25 min at 300,275 and 250℃,respectively.Besides,the composite started to take up hydrogen at room temperature and absorbed 2.0 wt.%hydrogen within 30 min at low temperature of 50℃.The hydrogenation activation energy of MgH_(2) was reduced from(72.5±2.7)to(18.8±0.2)kJ/mol after doping with 10 wt.%nano-Mn.In addition,the MgH_(2)+10 wt.%nano-Mn composite exhibited superior cyclic property,maintaining 92%initial capacity after 20 cycles.

Practical development and challenges of garnet-structured Li_(7)La_(3)Zr_(2)O_(12) electrolytes for all-solid-state lithium-ion batteries:A review

All-solid-state Li-ion batteries(ASSLIBs)have been widely studied to achieve Li-ion batteries(LIBs)with high safety and energy density.Recent reviews and experimental papers have focused on methods that improve the ionic conductivity,stabilize the electrochemical performance,and enhance the electrolyte/electrode interfacial compatibility of several solid-state electrolytes(SSEs),including oxides,sulfides,composite and gel electrolytes,and so on.Garnet-structured Li_(7)La_(3)Zr_(2)O_(12)(LLZO)is highly regarded an SSE with excellent application potential.However,this type of electrolyte also possesses a number of disadvantages,such as low ionic conductivity,unstable cubic phase,and poor interfacial compatibility with anodes/cathodes.The benefits of LLZO have urged many researchers to explore effective solutions to overcome its inherent limitations.Herein,we review recent developments on garnet-structured LLZO and provide comprehensive insights to guide the development of garnet-structured LLZO-type electrolytes.We not only systematically and comprehensively discuss the preparation,element doping,structure,stability,and interfacial improvement of LLZOs but also provide future perspectives for these materials.This review expands the current understanding on advanced solid garnet electrolytes and provides meaningful guidance for the commercialization of ASSLIBs.

Facile construction of Mxene-supported niobium hydride nanoparticles toward reversible hydrogen storage in magnesium borohydride

The facile construction of nanoscale NbH_(x)supported by Ti_(3)C_(2)(NbH_(x)@Ti_(3)C_(2))was achieved using facile ball milling strategy to improve the hydrogen desorption kinetics and reversibility of magnesium borohydride(Mg(BH_(4))_(2)).The doping of 30 wt%NbH_(x)@Ti_(3)C_(2)catalyst reduced the onset dehydrogenation temperature of Mg(BH_(4))_(2)to 71.2℃.Additionally,the Mg(BH_(4))_(2)+30NbH_(x)@Ti_(3)C_(2)composite achieved remarkable hydrogen release of over 9.2 wt%at a temperature as low as 230℃,indicating unexpected dehydrogenation kinetics.Moreover,the reversibility of NbH_(x)@Ti_(3)C_(2)doped Mg(BH_(4))_(2)was retained to more than 4.2 wt%after four cycles,which was increased by 68%compared to that of undoped Mg(BH_(4))_(2).The strong catalysis of NbH_(x)@Ti_(3)C_(2)catalyst could be attributed to the synergistic effect of NbH_(x)and Ti_(3)C_(2)in hydrogen spillover and diffusion.NbH_(x)acted as a"hydrogen pump"for effective hydrogen spillover,while Ti_(3)C_(2)created numerous diffusion channels for hydrogen dissolution and provided the active catalytic site to facilitate the re/dehydrogenation of Mg(BH_(4))_(2).

Optimizing FeCoNiCrTi high-entropy alloy with hydrogen pumping effect to boost de/hydrogenation performance of magnesium hydride

The exploration of efficient,long-lived and cost-effective transition metal catalysts is highly desirable for the practical hydrogen storage of magnesium hydride(MgH_(2)) in sustainable energy devices.Herein,FeCoNiCrTi high-entropy alloy(HEA) nanosheets were prepared via a facile wet chemical ball milling strategy and they were introduced into MgH_(2) to boost the hydrogen storage performance.The refined HEA exhibited superior catalytic activity on MgH_(2).In contrast to additive-free MgH_(2),the initial desorption temperature of the constructed MgH_(2)-HEA composite was reduced from 330.0 to 198.5℃ and a remarkable 51% reduction in the dehydrogenation activation energy was achieved.Besides,the MgH_(2)-HEA composite only required one-twentieth time of that consumed by pure MgH_(2) to absorb 5.0 wt% of H_(2) at 225℃.The synergy between the "hydrogen pumping" effect of Mg_2Ni/Mg_2NiH_4 and Mg_2Co/Mg_2CoH_5 couples,as well as the good dispersion of Fe,Cr and Ti on the surface of MgH_(2) contributed to the enhanced de/hydrogenation performance of the MgH_(2)-HEA composites.This study furnishes important steering for the design and fabrication of multiple transition metal catalysts and may push the commercial application of magnesium-based hydrides one step forward.

Recent advances in metastable alloys for hydrogen storage:a review

Development of new materials with high hydrogen storage capacity and reversible hydrogen sorp-tion performances under mild conditions has very high value in both fundamental and application aspects.In the past years,some new systems with metastable structures,such as ultra-fine nanocrystalline alloys,amorphous alloys,nanoglass alloys,immiscible alloys,high-entropy alloys,have been abundantly studied as hydrogen storage mate-rials.Many new hydrogen storage properties either from the kinetics or thermodynamics aspects have been reported.In this review,recent advances of studies on metastable alloys for hydrogen storage applications have been comprehensively reviewed.The materials preparation methods to synthesize metastable hydrogen storage alloys are firstly reviewed.Afterwards,hydrogen storage prop-erties of the metastable alloys are summarized and dis-cussed,focusing on the unique kinetics and thermodynamics properties by forming of such unique metastable structures.For examples,superior hydrogena-tion kinetics and higher hydrogen storage capacity have been achieved in Mg-based amorphous and nanoglass alloys.Destabilized thermodynamics properties can be obtained in the immiscible Mg-Mn and Mg-Zr alloys.In addition to highlighting the recent achievements of metastable alloys in the field of hydrogen storage,the remaining challenges and trends of the emerging research are also discussed.

Two-dimensional vanadium nanosheets as a remarkably effective catalyst for hydrogen storage in MgH_(2)

Magnesium hydride(MgH_(2)),which possesses high hydrogen density of 7.6 wt%,abundant resource and non-toxicity,has captured intense attention as one of the potential hydrogen storage materials.However,the practical application of Mg/MgH_(2) system is suffering from high thermal stability,sluggish absorption and desorption kinetics.Herein,two-dimensional(2D) vanadium nanosheets(V_(NS)) were successfully prepared via a facile wet chemical ball milling method and proved to be highly effective on improving the hydrogen storage performance of MgH_(2).For instance,the MgH_(2)+7 wt% V_(NS) composite began to release hydrogen at 187.2℃,152 ℃ lower than that of additive-free MgH_(2).At 300℃,6.3 wt% hydrogen was released from the MgH_(2)+7 wt% V_(NS) composite within 10 min.In addition,the fully dehydrogenated sample could absorb hydrogen even at room temperature under hydrogen pressure of 3.2 MPa.X-ray diffractometer(XRD) and transmission electron microscopy(TEM)results confirmed metallic vanadium served as catalytic unit for facilitating the de/rehydrogenation reaction of MgH_(2).This finding presents an example of facile synthesis of two-dimensional(2D) vanadium with excellent catalysis,which may shed light on future design and preparation of highly effective layered catalysts for hydrogen storage and other energy-related areas.

2022 roadmap on hydrogen energy from production to utilizations

Hydrogen has been always the hot topic,which drives a lot of researchers to study and explore hydrogenrelated projects and fields.The first subfield is hydrogen production with green and cost-effective means.Some methods have been intensively used for high-efficient hydrogen production,i.e.,catalytic chemical hydrogen generation,electrocatalytic hydrogen evolution,photocatalytic hydrogen evolution,photo-electrocatalytic hydrogen evolution.Most of them are driven by various catalysts.Moreover,the hydrogen storage is also an important question,which is also a present research hot topic,although the history is long with several decades.Hydrogen fuel cells have also obtained great attention due to the zero emissions.The related research mainly focuses on the cell systems and electrocatalysts used.Under this background,we invite some excellent research groups to write this progress on hydrogen from production to utilizations.Finally,we believe that this roadmap on hydrogen can give some useful guidance in future research.