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The La0.67Mg0.33Ni2.5Co0.5hydrogen storage alloy was prepared by the vacuum intermediate frequency induction furnace followed by annealing treatment. The pulverization degree of both the as-cast and annealed alloy powders after gaseous hydriding and dehydriding cycle was investigated and the discovery was that annealing treatment could hardly ameliorate their anti-pulverization ability. The element content of La, Mg, Ni and Co existing in electrolyte before and after the electrochemical cycles by using ICP-AES technology was also analyzed and it showed that a large amount of La and Mg were dissolved in the electrolyte, but the amount of dissolution for La and Mg significantly declined when the alloy was annealed. The XRD analysis revealed that all the alloys consisted of two main phases AB3and AB2and a residual phase AB5while annealing treatment made the AB2phase decrease slightly. Furthermore, the anti-corrosion abilities of various elements in different phases of the as-cast and annealed alloy samples were studied by analyzing the element (La, Mg, Ni, Co) change with the corrosion time in phases AB3and AB2by means of EDS. It turned out that the element of La was mainly corroded out from the phase AB2while not easily from the phase AB3. However, the element of Mg was both easily corroded out from the phases AB2and AB3, but the corrosion was more obvious in the phase AB3. Therefore, annealing improved the anti-corrosion performances of La and Mg in the phase AB2.

The catalytic effects of MnFe2O4nanoparticles on the hydrogen storage properties of MgH2–LiAlH4, prepared by ball milling, are studied for the first time. The hydrogen storage properties and reaction mechanism are investigated by pressure–composition–temperature (PCT), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The nonisothermal desorption results show that MgH2–LiAlH4+ 5 mol % MnFe2O4has a lower onset dehydrogenation temperature, 85, 50, and 40 °C lower than these of ball-milled MgH2–LiAlH4sample for each stage in the dehydrogenation process. The isothermal dehydriding kinetics and isothermal rehydrogenation kinetics results indicate that adding MnFe2O4to MgH2–LiAlH4could significantly enhance the absorption/desorption kinetics of MgH2–LiAlH4. From the differential scanning calorimetry and Kissinger analysis, the apparent activation energy of the 5 mol % MnFe2O4-doped sample for the three decomposition stage is 55.8, 70.8, and 96.5 kJ/mol, resulting in a 45.7, 85.5, and 99.6 kJ/mol decrease, respectively, compared with the MgH2–LiAlH4sample. These improvements are mainly attributed to in situ formed Fe0.872O phase and the amorphous Mn-containing phase during the dehydrogenation process, which act as the real catalyst in the MgH2–LiAlH4+ 5 mol % MnFe2O4composite.

The effects of NiFe2O4nanoparticles addition on the dehydrogenation behavior of LiAlH4were investigated. The onset dehydrogenation temperature for LiAlH4+3 mol % NiFe2O4sample is 61 °C, which decreased by 94 °C compared with the as-received LiAlH4and released ∼7.2 wt % hydrogen when heated to 180 °C. Isothermal desorption measurements show that the 3 mol % NiFe2O4-doped sample releases ∼7.0 wt % of hydrogen in 91 min at 120 °C, which is 6.3 wt % higher than the as-received LiAlH4under the same conditions. Through calculating the apparent activation energy of the LiAlH4samples with and without NiFe2O4for the first two dehydrogenation stages, the Eaof the LiAlH4+3 mol % NiFe2O4sample is 54.3 and 70.8 kJ/mol, resulting in 52.5 and 59% decrease, respectively, compared with the as-received LiAlH4. Analyzing the X-ray diffraction and Fourier transform infrared spectroscopy results, it is reasonable to believe that the remarkable improvement of dehydrogenation properties of NiFe2O4-doped LiAlH4results from the in situ formed LiFeO2and Al–Ni compounds, providing the active sites for nucleation and growth of the dehydrogenation products.

The catalytic effect of two nanoscale transition metal oxides, Fe2O3and Co2O3, as additives on the dehydrogenation properties of LiAlH4after milling are investigated. The onset dehydrogenation temperature for the 5 mol % Fe2O3-doped and 5 mol % Co2O3-doped samples are 85 and 79 °C lower for the first-stage and 60 and 45 °C lower for the second-stage, respectively, compared with the as-received LiAlH4. The isothermal dehydriding kinetics reveals that the 5 mol % Fe2O3-doped sample can release about 7.1 wt % hydrogen in 70 min at 120 °C, whereas as-received LiAlH4only releases 0.3 wt % hydrogen under the same conditions. From differential scanning calorimetry (DSC) and Kissinger desorption kinetics analyses, the apparent activation energies (Ea) of the 5 mol % Fe2O3-doped sample are 54.2 and 86.4 kJ/mol for the first two dehydrogenation stages, resulting in decreases of 42.8 and 50% compared with those of as-received LiAlH4, respectively, which are considerably lowered compared with LiAlH4doped with other reported catalysts calculated by Kissinger method. X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared (FTIR) analyses demonstrate that these finely dispersed Li2Fe2.4O4.6, Fe0.957O, and various Co oxides contribute to kinetics improvement by serving as active sites for nucleation and growth of dehydrogenated products.

The effects of nanosized MnFe2O4additive on the dehydrogenation properties of LiAlH4prepared by ball milling were investigated for the first time. It was found that the LiAlH4+ 7 mol % MnFe2O4sample started to decompose at 62 and 119 °C for the first two dehydrogenation stages and released 7.45 wt % hydrogen, which is 88 and 71 °C lower than those of as-received LiAlH4, respectively. The isothermal dehydriding kinetics show that the doped LiAlH4sample could release about 4.7 wt % hydrogen in 70 min at 90 °C. Furthermore, the first two dehydrogenation steps could be finished within 80 min with 7.44 wt % hydrogen released at 120 °C, whereas as-received LiAlH4only released about 0.5 wt % hydrogen for the same temperature and time. From differential scanning calorimetry (DSC) and Kissinger desorption kinetics analyses, the apparent activation energies, Ea, of the doped sample were 66.7 kJ/mol for the first dehydrogenation stage and 75.8 kJ/mol for the second dehydrogenation stage, resulting in decreases of 40.2% and 58.1% compared with those of as-received LiAlH4, which are much higher than those of LiAlH4doped with other reported catalysts calculated by Kissinger method. Through X-ray diffraction (XRD) and Fourier transform infrared (FTIR) observations, in situ formed Fe0.9536O and amorphous Mn or Mn-containing phases together provide a synergetic catalytic effect for the remarkably improved dehydrogenation properties of LiAlH4.