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.

Heterogeneous GdTbDyCoAl high-entropy alloy with distinctive magnetocaloric effect induced by hydrogenation

Developing novel magnetocaloric materials is of great significance for the applications of magnetic refrigeration.In this study,we designed a heterogeneous rare-earth-based high-entropy alloy(HEA)comprising amorphous matrix,local crystal-like cluster and nanocrystalline dihydride with average size of 7.5 nm through isothermal hydrogenation.This heterogeneous structure can significantly tune the magnetocaloric effect of alloy.After hydrogenation,the predominant exchange interaction transforms from ferromagnetic to antiferromagnetic with the disappearance of spin-glass-like behavior,and a complete second-order magnetic transition is obtained.Compared with the Gd_(20)Tb_(18)Dy_(18)Co_(20)Al_(24) high-entropy metallic glass with a small number of nanocrystals,the maximum magnetic entropy change of the hydrogen-containing HEA is increased from 8.8 to 13.6 J kg^(-1)K^(-1) under applied magnetic field change of 5 T accompanying unobvious hysteresis and decreased magnetic transition temperature from 59 to 8 K,which is more promising as magnetic refrigerant at cryogenic temperature.This work provides a novel concept of designing heterogeneous structure in terms of special cluster and preferential nanocrystalline to modulate the properties of metallic glasses.