Hydrogen storage properties of Li-Mg-N-B-H/ZrCoH_(3) composite with different ball-milling atmospheres

Li-Mg-N-B-H/ZrCoH_(3) composites were successfully synthesized by ball milling of the reactants under argon and hydrogen atmosphere,respectively.The composite synthesized by reactive ball milling(RBM)under hydrogen has the best hydrogen storage properties.It can desorb 3.71 wt%hydrogen in 60 min at 150℃under pressure of 0.1 MPa,and the dehydrogenation capacity reaches 4.59 wt%in 8 h.For the re-hydrogenation,5.27 wt%hydrogen was absorbed in only 10 min at 150℃under H_(2) pressure of 8 MPa.The phases of the as-milled and subsequently dehydrogenated and re-hydrogenated samples were determined by X-ray diffraction(XRD).The microstructures and elemental distributions were characterized by scanning electron microscope(SEM)and energy-dispersive spectrometer(EDS)measurements.It is shown that Mg is in situ hydrogenated and introduced homogeneous distribution of ZrCoH_(3) particles during the RBM process under hydrogen atmosphere.The activation energies for the composites were calculated by Kissinger method through differential scanning calorimetric(DSC)measurements for the dehydrogenation process with different heating rates.It is determined that the activation energy for the Li-Mg-N-B-H/ZrCoH_(3) composite synthesized by RBM under hydrogen is 79.9 kJ·mol^(-1),which is14 kJ·mol^(-1) lower than that for the sample without ZrCoH_(3) addition.The N-H bond energies were analyzed by infrared(IR)absorption spectrum,and the reasons for weakening of the N-H bond were further discussed.

Hydrogenation properties of(V_(0.85)Fe_(0.15))_(100-x)M_(x)-Ce BCC solid solution alloys with M=Cr,Mo,Al

The structure and hydrogenation properties of (V_(0.85)Fe_(0.15))_(100-x)M_(x)-Ce(x=0,1,3,5;at%) alloys with M=Cr,Mo,Al were investigated.All the alloys show the same phase composition consisting of BCC matric and CeO_(2)phases which distribute along the grain boundary.The hydrogen capacities of (V_(0.85)Fe_(0.15))_(100-x)M_(x)-Ce change little with M,and none of them exceeds 2.0 wt%.But the plateau pressure shows remarkable linearly variation with the amount of M and the lattice parameter of BCC matric.The additions of Cr,Mo and A1 raise the plateau,but the linear relation of plateau versus BCC lattice parameter of Mo/Al-added alloys is opposite to that of Cr-added alloys and many other conventional hydrogen storage alloys.The radius of hydrogen site is introduced to explain the inconsistent.The plateau pressure of (V_(0.85)Fe_(0.15))_(100-x)M_(x)-Ce with any kind of M added increases with the contraction of the hydrogen site.The plateau pressure of (V_(0.85)Fe_(0.15))_(100-x)M_(x)-Ce can also be reflected by the stability of hydride which is judged by the enthalpy change during the dehydrogenation.

Mechanochemistry and hydrogen storage properties of 2Li_(3)N+Mg mixture

The Li-Mg-N-H hydrogen storage system is a promising hydrogen storage material due to its moderate operation temperature,good reversibility,and relatively high capacity.In this work,the Li-Mg-N-H composite was directly synthesized by reactive ball milling(RBM) of Li3N and Mg powder mixture with a molar ratio of 2:1 under hydrogen pressure of 9 MPa.More than 8.8 wt%hydrogen was absorbed during the RBM process.The phases and structural evolution during the in situ hydrogenation process were analyzed by means of in situ solidgas absorption and ex situ X-ray diffraction(XRD) measurements.It is determined that the hydrogenation can be divided into two steps,leading to mainly the formation of a lithium magnesium imide phase and a poorly crystallized amide phase,respectively.The H-cycling properties of the as-milled composite were determined by temperature-programmed dehydrogenation(TPD) method in a closed system.The onset dehydrogenation temperature was detected at 125℃,and it can reversibly desorb 3.1 wt% hydrogen under a hydrogen back pressure of 0.2 MPa.The structural evolution during dehydrogenation was further investigated by in situ XRD measurement.It is found that Mg(NH_(2))_(2)phase disappears at about 200 ℃,and Li_(2)Mg_(2)N_(3)H_(3),LiNH_(2),and Li_(2)MgN_(2)H_(2)phases coexist at even 300 ℃,revealing that the dehydrogenation process is step-wised and only partial hydrogen can be desorbed.

Heat treatment effect on structural evolution and hydrogen sorption properties of Y_(0.5)La_(0.2)Mg_(0.3-x)Ni_(2) compound

The effect of heat treatment on phase occurrence,crystal structures and hydrogen sorption properties of Y_(0.5)La_(0.2)Mg_(0.3-x)Ni_(2) compounds has been investigated.The targeted compounds were synthesized through induction melting and processed heat treatment at 700 and 900℃,respectively.Phase occurrence and structural properties were studied by X-ray powder diffraction(XRD).The global compositions and phase compositions have been determined by inductively coupled plasma-optical emission spectrometer(ICP-AES) and electron probe microanalysis(EPMA) respectively.

Thermal storage properties of Mg with synergistic effect of LaNi and TiH_(2)

The effect of LaNi and Ti on thermal storage properties of MgH_(2)was investigated.The thermal storage performances of Mg are significantly improved by adding LaNi and Ti.The pressure-composition-temperature(PCT)curves indicate that the formation enthalpy for Mg-15 wt%Ti-5 wt%LaNi sample is 73.00 kJ·mol^(-1),which approaches to the theoretical values of pure MgH_(2).The isothermal measurement indicates that,for the Mg-15wt%Ti-5 wt%LaNi,the first absorption reaction fraction within 2 min is 93.77%,increasing by 0.32%,0.24%and0.08%compared with those for Mg,Mg-5 wt%LaNi and Mg-15 wt%Ti,respectively.The first desorption reaction fraction within 2 min is 73.18%,increasing by 55.91%,9.79%and 8.12%compared with those for Mg,Mg-5wt%LaNi and Mg-15 wt%Ti,respectively.Moreover,Mg-15 wt%Ti-5 wt%LaNi has the best cyclic stability in all the samples.The thermal storage performances of Mg by adding both LaNi and Ti are improved mainly ascribed to synergistic effect of in situ formed La_(4)H_(12.19),Mg_(2)NiH_(4),H_(0.3)Mg_(2)Ni and TiH_(2)particles during cyclic process.The above analysis demonstrates that Mg-15 wt%Ti-5wt%LaNi is suitable for using as a heat storage material.

Thermal storage properties of Mg-LaNi using as a solar heat storage material

The effect of LaNi on thermal storage properties of MgH2 prepared by ball milling under hydrogen atmosphere was investigated.The thermal storage properties,cyclic property and thermal storage mechanism were studied by pres sure-composition-temperature(PC T),X-ray diffraction(XRD)and transmission electron microscopy(TEM).The Van't Hoff curve indicates that the formation enthalpy of Mg-16 wt%LaNi is 74.62 kJ·mol^(-1),which approaches to the theoretical values of MgH2.The isothermal measurement indicates that Mg-16 wt%LaNi can absorb 6.263 wt%H_(2)within 30 min at 390℃for the first absorption,the absorption reaction fraction within2 min is over 90.00%,and the desorption reaction fraction within 2 min is 72.63%,increasing by 55.36%compared with that of Mg.Mg-16 wt%LaNi has better cyclic stability than that of Mg,only decreasing by 0.609 wt%after 80cycles.The enhancement in thermal storage performances of Mg by adding LaNi is mainly ascribed to the formed Mg_(2)NiH_(4),H_(0.3)Mg_(2)Ni and La_(4)H_(12.19)during the cyclic process which act as catalysts and inhibit the growth of Mg.The above results prove that Mg-16 wt%LaNi is suitable for use as a heat storage material.