Desorption properties of LiAlH4 doped with LaFeO3 catalyst

The addition of a catalyst and ball milling process was found to be one of the efficient method to reduce the decomposition temperature and improve the desorption kinetics of lithium aluminium hydride (LiAlH₄). In this paper, a transition metal oxide, LaFeO₃ was used as a catalyst. Decomposition temperature of the 10 wt% of LaFeO₃-doped LiAlH₄ system was found to be lowered from 143 °C to 103 °C (first step) and from 175 °C to 153 °C (second step), respectively. In isothermal desorption kinetics, the amount of hydrogen released of the doped sample was improved to 3.9 wt% in 2.5 h at 90 °C. Meanwhile, the undoped sample had released less than 1.0 wt% of hydrogen under the same condition. The activation energy of the LaFeO₃-doped LiAlH₄ sample was measured to be 73 kJ/mol and 90 kJ/mol for the first two dehydrogenation reactions compared to 107 kJ/mol and 119 kJ/mol for the undoped sample. The improvements of desorption properties were the results from the formation of LiFeO₂, Fe and La or La-containing phase during the heating process.     

Catalytic effects of MgFe2O4 addition on the dehydrogenation properties of LiAlH4

Study on the catalytic roles of MgFe₂O₄ on the dehydrogenation performance of LiAlH₄ was carried out for the first time. Notable improvement on the dehydrogenation of LiAlH₄–MgFe₂O₄ compound was observed. The initial decomposition temperatures for the catalyzed LiAlH₄ were decreased to 95 °C and 145 °C for the first and second stage reactions, which were 48 °C and 28 °C lower than the milled LiAlH₄. As for the desorption kinetics performance, the MgFe₂O₄ doped-LiAlH₄ sample was able to desorb faster with a value of 3.5 wt% of hydrogen in 30 min (90 °C) while the undoped LiAlH₄ was only able to desorb 0.1 wt% of hydrogen. The activation energy determined from the Kissinger analysis for the first two desorption reactions were 73 kJ/mol and 97 kJ/mol; which were 31 and 17 kJ/mol lower as compared to the milled LiAlH₄. The X-ray diffraction result suggested that the MgFe₂O₄ had promoted significant improvements by reducing the LiAlH₄ decomposition temperature and faster desorption kinetics through the formation of active species of Fe, LiFeO₂ and MgO that were formed during the heating process.     

Mechanochemical modification of LiAlH4 with Fe2O3 - A combined DFT and experimental study

LiAlH₄ is a promising material for hydrogen storage, having the theoretical gravimetric density of 10.6 wt% H₂. In order to decrease the temperature where hydrogen is released, we investigated the catalytic influence of Fe₂O₃ on LiAlH₄ dehydrogenation, as a model case for understanding the effects transition oxide additives have in the catalysis process. Quick mechanochemical synthesis of LiAlH₄ + 5 wt% Fe₂O₃ led to the significant decrease of the hydrogen desorption temperature, and desorption of over 7 wt%H₂ in the temperature range 143–154 °C. Density functional theory (DFT)-based calculations with Tran-Blaha modified Becke-Johnson functional (TBmBJ) address the electronic structure of LiAlH₄ and Li₃AlH₆. ⁵⁷Fe Mössbauer study shows the change in the oxidational state of iron during hydrogen desorption, while the ¹H NMR study reveals the presence of paramagnetic species that affect relaxation. The electron transfer from hydrides is discussed as the proposed mechanism of destabilization of LiAlH₄ + 5 wt% Fe₂O₃.     

Ultra-fast dehydrogenation behavior at low temperature of LiAlH4 modified by fluorographite

LiAlH₄ modified by different weight ratios of fluorographite (FGi) can be synthesized through mechanical ball-milling and their dehydrogenation behaviors were investigated. LiAlH₄ particles distributed on the FGi surface with greatly decreased sizes are achieved, comparing with ball-milled pristine LiAlH₄. Greatly reduced dehydrogenation temperatures are discovered in LiAlH₄-FGi composites. Among these composites, LiAlH₄-40FGi composite exhibits an ultra-fast hydrogen release at very low temperature as 61.2 °C, and 5.7 wt% hydrogen is liberated in seconds. Besides, the released hydrogen is of high purity according to MS test. Furthermore, XRD analysis on the dehydrogenated products proves that FGi changes the dehydrogenation reaction pathway of LiAlH₄, through which the dehydrogenation reaction enthalpy change is remarkably reduced, leading to greatly improved hydrogen desorption properties. Such investigations have discovered the potential of solid-state way of producing hydrogen under ambient temperatures.     

Enhanced hydrogen storage properties of TiN–LiAlH4 composite

The hydrogen storage properties of LiAlH₄ doped efficient TiN catalyst were systematically investigated. We observe that TiN catalyst enhances the dehydrogenation kinetics and decreases the dehydrogenation temperature of LiAlH₄. The dehydrogenation behaviors of 2%TiN–LiAlH₄ are investigated using temperature programmed desorption (TPD), differential scanning calorimetry (DSC) and fourier transform infrared spectroscopy (FTIR). Interestingly, the onset hydrogen desorption temperature of 2%TiN–LiAlH₄ sample gets lowered from 151.0 °C to 90.0 °C with a faster kinetics, and the dehydrogenation rate reached a maximum value at 137.2 °C. By adding a small amount of as-prepared TiN, approximately 7.1 wt% of hydrogen can be released from the LiAlH₄ at 130 °C. Interestingly, the result of the FTIR indicates that the 2%TiN–LiAlH₄ maybe restore hydrogen under 5.5 MPa hydrogen. Moreover, 2%TiN–LiAlH₄ displayed a substantially reduced activation energy for LiAlH₄ dehydrogenation.     

Catalytic effects of FGO-Ni addition on the dehydrogenation properties of LiAlH4

LiAlH₄ is an ideal hydrogen storage material with a theoretical hydrogen storage capacity of 10.6 wt%. In order to reduce the hydrogen release temperature and increase the hydrogen release amount of LiAlH₄, multilayer graphene oxide and nickel (FGO-Ni) composite catalyst were prepared by physical ball milling and doped into LiAlH₄. The effect of FGO-Ni composite catalyst on the dehydrogenation performance of LiAlH₄ was studied by pressure-composition-temperature apparatus, scanning electron microscope (SEM) and X-ray diffractometer. The results show that, compared with pure LiAlH₄, the hydrogen release time of LiAlH₄ doped with 9 wt%FGO-3wt%Ni is obviously shortened about 90min at 150 °C and the hydrogen release amount of LiAlH₄ doped with 9 wt%FGO-3wt%Ni also increased 1.8 wt%. Importantly, the dehydrogenation amount of LiAlH₄ (9 wt%FGO)-3wt% could reach 4 wt% at 135 °C which was 4 times higher than that of the pure LiAlH₄. At the same temperature, the hydrogen release of pure LiAlH₄ was only 0.84 wt%. In contrast, doping FGO-Ni composite catalyst reduces the hydrogen release temperature of LiAlH₄ and weakens the hydrogen release barrier. Forthermore, SEM results showed that doping FGO-Ni reduced the agglomeration between LiAlH₄ particles and increased the specific surface area of the sample, which improving the hydrogen release properties of LiAlH₄.     

Enhancement of the H2 desorption properties of LiAlH4 doping with NiCo2O4 nanorods

Lithium aluminum hydride (LiAlH₄) is considered as an attractive candidate for hydrogen storage owing to its favorable thermodynamics and high hydrogen storage capacity. However, its reaction kinetics and thermodynamics have to be improved for the practical application. In our present work, we have systematically investigated the effect of NiCo₂O₄ (NCO) additive on the dehydrogenation properties and microstructure refinement in LiAlH₄. The dehydrogenation kinetics of LiAlH₄ can be significantly increased with the increase of NiCo₂O₄ content and dehydrogenation temperature. The 2 mol% NiCo₂O₄-doped LiAlH₄ (2% NCO–LiAlH₄) exhibits the superior dehydrogenation performances, which releases 4.95 wt% H₂ at 130 °C and 6.47 wt% H₂ at 150 °C within 150 min. In contrast, the undoped LiAlH₄ sample just releases <1 wt% H₂ after 150 min. About 3.7 wt.% of hydrogen can be released from 2% NCO–LiAlH₄ at 90 °C, where total 7.10 wt% of hydrogen is released at 150 °C. Moreover, 2% NCO–LiAlH₄ displayed remarkably reduced activation energy for the dehydrogenation of LiAlH₄.     

Significantly improved dehydrogenation of LiAlH4 destabilized by K2TiF6

The effects of K₂TiF₆ on the dehydrogenation properties of LiAlH₄ were investigated by solid-state ball milling. The onset decomposition temperature of 0.8 mol% K₂TiF₆ doped LiAlH₄ is as low as 65 °C that 85 °C lower than that of pristine LiAlH₄. Isothermal dehydrogenation properties of the doped LiAlH₄ were studied by PCT (pressure–composition–temperature). The results show that, for the 0.8 mol% K₂TiF₆ doped LiAlH₄ that dehydrogenated at 90 °C, 4.4 wt% and 6.0 wt% of hydrogen can be released in 60 min and 300 min, respectively. When temperature was increased to 120 °C, the doped LiAlH₄ can finish its first two dehydrogenation steps in 170 min. DSC results show that the apparent activation energy (E_a) for the first two dehydrogenation steps of LiAlH₄ are both reduced, and XRD results suggest that TiH₂, Al₃Ti, LiF and KH are in situ formed, which are responsible for the improved dehydrogenation properties of LiAlH₄.     

Catalytic effect of Al2TiO5 on the dehydrogenation properties of LiAlH4

Lithium alanate (LiAlH₄) is considered as a promising material for storing hydrogen (H₂) in solid-state form for onboard applications due to its advantage of high gravimetric H₂ capacity. LiAlH₄ could release H₂ ～7.9 wt.% when heated up to ～250 °C. Nevertheless, the high desorption temperature, sluggish desorption kinetics, and irreversibility hamper the application of LiAlH₄ for solid-state H₂ storage materials. Therefore, in this study, we have used aluminum titanate (Al₂TiO₅) as an additive to diminish the desorption temperature and enhance the desorption kinetics of LiAlH₄. The addition of a small amount of Al₂TiO₅ (5 wt.%) into LiAlH₄ significantly decreased the decomposition temperature and enhanced the desorption kinetics, in which Al₂TiO₅-doped LiAlH₄ started to release H₂ at ～90 °C and was able to desorb H₂ as much as ～3.5 wt.% at 90 °C within 1 h. Without the catalyst, pure LiAlH₄ starts to release H₂ at ～145 °C and only desorbs H₂ as low as 0.3 wt.% at 90 °C within 1 h. The activation energies for H₂ release in the two-step desorption process of LiAlH₄ were reduced after catalysis with Al₂TiO₅. The activation energies of as-milled LiAlH₄ were 80 kJ/mol and 91 kJ/mol, respectively, as calculated by the Arrhenius plot. The activation energies were lowered to 68 kJ/mol and 79 kJ/mol after milling with Al₂TiO₅. The scanning electron microscopy images revealed that the LiAlH₄ particles became smaller and less agglomerated when Al₂TiO₅ was added. It is believed that the in-situ formation of active species during the desorption process and reduction in particles size play a vital role in improving the dehydrogenation properties of the Al₂TiO₅-doped LiAlH₄ system.     

Significantly improved dehydrogenation of LiAlH4 catalysed with TiO2 nanopowder

The effects of TiO₂ nanopowder addition on the dehydrogenation behaviour of LiAlH₄ have been studied. The 5 wt.% TiO₂-added LiAlH₄ sample showed a significant improvement in dehydrogenation rate compared to that of undoped LiAlH₄, with the dehydrogenation temperature reduced from 150 °C to 60 °C. Kinetic desorption results show that the added LiAlH₄ released about 5.2 wt% hydrogen within 30 min at 100 °C, while the as-received LiAlH₄ just released below 0.2 wt.% hydrogen within same time at 120 °C. From the Arrhenius plot of the hydrogen desorption kinetics, the apparent activation energy is 114 kJ/mol for pure LiAlH₄ and 49 kJ/mol for the 5 wt.% TiO₂ added LiAlH₄, indicating that TiO₂ nanopowder adding significantly decreased the activation energy for hydrogen desorption of LiAlH₄. X-ray diffraction and Fourier transform infrared analysis show that there is no phase change in the cell volume or on the Al-H bonds of the LiAlH₄ due to admixture of TiO₂ after milling. X-ray photoelectron spectroscopy results show no changes in the Ti 2p spectra for TiO₂ after milling and after dehydrogenation. The improved dehydrogenation behaviour of LiAlH₄ in the presence of TiO₂ is believed to be due to the high defect density introduced at the surfaces of the TiO₂ particles during the milling process.     

CoFe2O4 synthesized via a solvothermal method for improved dehydrogenation of NaAlH4

The effect of cobalt ferrite (CoFe₂O₄) nanopowder synthesised through a solvothermal method on the dehydrogenation properties of sodium alanate (NaAlH₄) was studied for the first time. The onset decomposition temperature of NaAlH₄ is significantly reduced after milling with CoFe₂O₄, in which the 10 wt% CoFe₂O₄-doped NaAlH₄ sample starts to decompose at ～100 °C. In contrast, the as-milled NaAlH₄ begins to decompose at ～200 °C, ～100 °C higher than the doped sample. With respect to desorption kinetic at constant temperature of 150 °C, the 10 wt% CoFe₂O₄-doped NaAlH₄ sample desorbed ～2.2 wt% hydrogen within 30 min, whereas the as-milled NaAlH₄ only desorbed below 0.2 wt% hydrogen. The Kissinger plot exhibited that the apparent activation energy (E_A) for hydrogen release from NaAlH₄ is significantly reduced after adding with 10 wt% CoFe₂O₄-doped NaAlH₄. The E_A values for the first and second stage dehydrogenation of the 10 wt% CoFe₂O₄-doped NaAlH₄ composite are calculated as 80.3 and 88.2 kJ/mol, respectively, and these values are reduced at approximately 34.3 and 30.5 kJ/mol compared with the as-milled NaAlH₄ (114.6 and 118.7 kJ/mol, respectively). Based on the X-ray diffraction result, the enhancement of desorption properties of NaAlH₄ with the presence of CoFe₂O₄ is presumably due to the synergistic catalytic effect played by new active species (Co₃O₄ and Fe) that in situ formed during the desorption process.     

LiAlH4–ZrCl4 mixtures for hydrogen release at near room temperature

The dehydrogenation temperature of LiAlH₄ was significantly reduced by the production of mixtures with ZrCl₄. Stoichiometric 4:1, and 5 mol % mixtures of LiAlH₄ and ZrCl₄ were produced by ball milling at room temperature and ?196 °C, and tested for dehydrogenation at low temperature. Cryogenic ball-milling resulted in an effective way to produce reactive mixtures for hydrogen release; because of achieving small aggregates size (5–20 μm) in 10 min of cryomilling while preventing substantial decomposition during preparation. Dehydrogenation reaction in the mixtures LiAlH₄/ZrCl₄ started around 31–47 °C under different heating rates. Partial dehydrogenation was proved at 70 °C: 4.4 wt % for the 5 mol% ZrCl₄–LiAlH₄ mixture, and 3.4 wt % for the best 4:1 stoichiometric mixture. Complete dehydrogenation up to 250 °C released 6.4 wt% and 4.1 wt%, respectively. Dehydrogenation reactions are exothermic, and the LiAlH₄/ZrCl₄ mixtures are unstable and difficult to handle. The activation energy of the exothermic reactions was estimated as 113.5 ± 9.8 kJ/mol and 40.6 ± 6.6 kJ/mol for 4LiAlH₄+ZrCl₄ and 5%mol ZrCl₄+LiAlH₄ samples milled in cryogenic conditions, respectively. The dehydrogenation pathway was changed in the LiAlH₄/ZrCl₄ mixtures as compared to pure LiAlH₄. Dehydrogenation reaction is proposed to form Al, LiCl, Zr, and H₂ as main products. Modification of the dehydrogenation reaction of LiAlH₄ was achieved at the cost of reducing the total hydrogen release capacity.     

Enhanced hydrogen storage performance of LiAlH4-MgH2-TiF3 composite

The mutual destabilization of LiAlH₄ and MgH₂ in the reactive hydride composite LiAlH₄-MgH₂ is attributed to the formation of intermediate compounds, including Li-Mg and Mg-Al alloys, upon dehydrogenation. TiF₃ was doped into the composite for promoting this interaction and thus enhancing the hydrogen sorption properties. Experimental analysis on the LiAlH₄-MgH₂-TiF₃ composite was performed via temperature-programmed desorption (TPD), differential scanning calorimetry (DSC), isothermal sorption, pressure-composition isotherms (PCI), and powder X-ray diffraction (XRD). For LiAlH₄-MgH₂-TiF₃ composite (mole ratio 1:1:0.05), the dehydrogenation temperature range starts from about 60 °C, which is 100 °C lower than for LiAlH₄-MgH₂. At 300 °C, the LiAlH₄-MgH₂-TiF₃ composite can desorb 2.48 wt% hydrogen in 10 min during its second stage dehydrogenation, corresponding to the decomposition of MgH₂. In contrast, 20 min was required for the LiAlH₄-MgH₂ sample to release so much hydrogen capacity under the same conditions. The hydrogen absorption properties of the LiAlH₄-MgH₂-TiF₃ composite were also improved significantly as compared to the LiAlH₄-MgH₂ composite. A hydrogen absorption capacity of 2.68 wt% under 300 °C and 20 atm H₂ pressure was reached after 5 min in the LiAlH₄-MgH₂-TiF₃ composite, which is larger than that of LiAlH₄-MgH₂ (1.75 wt%). XRD results show that the MgH₂ and LiH were reformed after rehydrogenation.     

Influence of K2TiF6 additive on the hydrogen sorption properties of MgH2

In this study, the hydrogen storage properties of MgH₂ with the addition of K₂TiF₆ were investigated for the first time. The temperature-programmed desorption results showed that the addition of 10 wt% K₂TiF₆ to the MgH₂ exhibited a lower onset desorption temperature of 245 °C, which was a decrease of about 105 °C and 205 °C compared with the as-milled and as-received MgH₂, respectively. The dehydrogenation and rehydrogenation kinetics of 10 wt% K₂TiF₆-doped MgH₂ were also significantly improved compared to the un-doped MgH₂. The results of the Arrhenius plot showed that the activation energy for the hydrogen desorption of MgH₂ was reduced from 164 kJ/mol to 132 kJ/mol after the addition of 10 wt% K₂TiF₆. Meanwhile, the X-ray diffraction analysis showed the formation of a new phase of potassium hydride and titanium hydride together with magnesium fluoride and titanium in the doped MgH₂ after the dehydrogenation and rehydrogenation process. It is reasonable to conclude that the K₂TiF₆ additive doped with MgH₂ played a catalytic role through the formation of active species of KH, TiH₂, MgF₂ and Ti during the ball milling or heating process. It is therefore proposed that this newly developed product works as a real catalyst for improving the hydrogen sorption properties of MgH₂.     

Improved reversible hydrogen storage of LiAlH4 by nano-sized TiH2

Transition metal halides are mostly used as dopants to improve the hydrogen storage properties of LiAlH₄, but they will cause hydrogen capacity loss because of their relatively high molecular weights and reactions with LiAlH₄. To overcome these drawbacks, active nano-sized TiH₂ (TiH₂^nano) prepared by reactive ball milling is used to dope LiAlH₄. It shows superior catalytic effect on the dehydrogenation of LiAlH₄ compared to commercial TiH₂. TiH₂^nano-doped LiAlH₄ starts to release hydrogen at 75 °C, which is 80 °C lower than the onset dehydrogenation temperature of commercial LiAlH₄. About 6.3 wt.% H₂ can be released isothermally at 100 °C (800 min) or at 120 °C (150 min). The apparent activation energies of the first two dehydrogenation reactions of LiAlH₄ are reduced by about 20 and 24 kJ mol⁻¹, respectively. Meanwhile, the regeneration of LiAlH₄ is realized through extracting the solvent from LiAlH₄·4THF, which is obtained by ball milling the dehydrogenated products of TiH₂^nano-doped LiAlH₄ in the presence of THF and 5 MPa H₂. This suggests that TiH₂ is also an effective catalyst for the formation of LiAlH₄·4THF.     

Effect of adding different percentages of HfCl4 on the hydrogen storage properties of MgH2

Magnesium hydride (MgH₂) is the best candidate material to store hydrogen in the solid-state form owing to its advantages such as good reversibility, high hydrogen storage capacity (7.6 wt%), low raw material cost and abundance in the earth. Nevertheless, slow desorption/absorption kinetics and high thermodynamic stability are two issues that have constrained the commercialization of MgH₂ as a solid-state hydrogen storage material. So, to boost the desorption/absorption kinetics and to alter the thermodynamics of MgH₂, hafnium tetrachloride (HfCl₄) was used as a catalyst in this study. Different percentages of HfCl₄ (5, 10, 15 and 20 wt%) were added to MgH₂ and their catalytic influences on the hydrogen storage properties of MgH₂ were investigated. Results showed that the 15 wt% HfCl₄-doped MgH₂ sample was the best composite to enhance the hydrogen storage performance of MgH₂. The onset decomposition temperature of the 15 wt% HfCl₄-doped MgH₂ composite was decreased by ~75 °C compared to as-milled MgH₂. Meanwhile, the desorption/absorption kinetic measurements showed an improvement compared to the undoped MgH₂. From the Kissinger analysis, the apparent dehydrogenation activation energy was 167.0 kJ/mol for undoped MgH₂ and 102.0 kJ/mol for 15 wt% HfCl₄-doped MgH₂. This shows that the HfCl₄ addition reduced the activation energy of the hydrogen decomposition of MgH₂. The desorption enthalpy change calculated by the van't Hoff equation showed that the addition of HfCl₄ to MgH₂ did not affect the thermodynamic properties. Scanning electron microscopy showed that the size of the MgH₂ particles decreased and there was less agglomeration after the addition of HfCl₄. It is believed that the decrease in the particle size and in-situ generated MgCl₂ and Hf-containing species had synergistic catalytic effects on enhancing the hydrogen storage properties of the HfCl₄-doped MgH₂ composite.     

Modifying the hydrogen storage performances of NaBH4 by catalyzing with MgFe2O4 synthesized via hydrothermal method

In this study, the hydrogenation performance of NaBH₄ was modified by the addition of 10 wt% MgFe₂O₄ as the catalyst. The NaBH₄ + 10 wt% of MgFe₂O₄ sample was prepared by a ball milling technique. The onset decomposition temperature of MgFe₂O₄-doped NaBH₄ was decreased to 323 °C and 483 °C for the first and second stage of dehydrogenation as compared to the milled NaBH₄ (497 °C). The desorption kinetics study showed that the addition of MgFe₂O₄ caused the sample to had faster hydrogen desorption with a capacity of 6.2 wt% within 60 min while the milled NaBH₄ had only released 5.3 wt% of hydrogen in the same period of time. For the isothermal absorption kinetics, the total amount of hydrogen absorbed by the milled NaBH₄ was 3.7 wt% while the NaBH₄ + 10 wt% MgFe₂O₄ sample showed better absorption characteristic with a total amount of 4.5 wt% of hydrogen within 60 min. The calculated desorption activation energy from the Kissinger plot of NaBH₄ + 10 wt% MgFe₂O₄ sample was 187 kJ/mol which reduced by 28 kJ/mol than the milled NaBH₄ (215 kJ/mol). The in-situ formation of MgB₆ and Fe₃O₄ after the dehydrogenation process indicates that these new species were responsible for the improved hydrogenation performances of NaBH₄.     

Synthesis of low-cost biomass charcoal-based Ni nanocatalyst and evaluation of their kinetic enhancement of MgH2

In this study, a low-cost biomass charcoal (BC)-based nickel catalyst (Ni/BC) was introduced into the MgH₂ system by ball-milling. The study demonstrated that the Ni/BC catalyst significantly improved the hydrogen desorption and absorption kinetics of MgH₂. The MgH₂ + 10 wt% Ni/BC-3 composite starts to release hydrogen at 187.8 °C, which is 162.2 °C lower than the initial dehydrogenation temperature of pure MgH₂. Besides, 6.04 wt% dehydrogenation can be achieved within 3.5 min at 300 °C. After the dehydrogenation is completed, MgH₂ + 10 wt% Ni/BC-3 can start to absorb hydrogen even at 30 °C, which achieved the absorption of 5 wt% H₂ in 60 min under the condition of 3 MPa hydrogen pressure and 125 °C. The apparent activation energies of dehydrogenation and hydrogen absorption of MgH₂ + 10 wt% Ni/BC-3 composites were 82.49 kJ/mol and 23.87 kJ/mol lower than those of pure MgH₂, respectively, which indicated that the carbon layer wrapped around MgH₂ effectively improved the cycle stability of hydrogen storage materials. Moreover, MgH₂ + 10 wt% Ni/BC-3 can still maintain 99% hydrogen storage capacity after 20 cycles. XRD, EDS, SEM and TEM revealed that the Ni/BC catalyst evenly distributed around MgH₂ formed Mg₂Ni/Mg₂NiH₄ in situ, which act as a “hydrogen pump” to boost the diffusion of hydrogen along with the Mg/MgH₂ interface. Meanwhile, the carbon layer with fantastic conductivity enormously accelerated the electron transfer. Consequently, there is no denying that the synergistic effect extremely facilitated the hydrogen absorption and desorption kinetic performance of MgH₂.     

Improving the hydrogen storage performance of lithium borohydride by Ti3C2 MXene

Two-dimensional layered material of Ti₃C₂ has been used to improve the hydrogen desorption properties of LiBH₄. The results of temperature-programmed dehydrogenation (TPD) and isotherm dehydrogenation (TD) demonstrate that adding the Ti₃C₂ contributes to the hydrogen storage performance of LiBH₄. The dehydrogenation temperature decreases and the dehydrogenation rate increases with increasing the adding amounts of Ti₃C₂. The onset dehydrogenation temperature of LiBH₄ + 40 wt% Ti₃C₂ composite is 120 °C and approximately 5.37 wt% hydrogen is liberated within 1 h at 350 °C. Furthermore, the activation energy of LiBH₄ + wt.% Ti₃C₂ is also greatly reduced to 70.3 kJ/mol, much lower than that of pure LiBH₄. The remarkable dehydrogenation property of the LiBH₄+ 40 wt% Ti₃C₂ may be due to the layered active Ti-containing Ti₃C₂ and the high surface area of MXene.     

Enhancing hydrogen storage performance of MgH2 through the addition of BaMnO3 synthesized via solid-state method

Currently, magnesium hydride (MgH₂) as a solid-state hydrogen storage material has become the subject of major research owing to its good reversibility, large hydrogen storage capacity (7.6 wt%) and affordability. However, MgH₂ has a high decomposition temperature (>400 °C) and slow desorption and absorption kinetics. In this work, BaMnO₃ was synthesized using the solid-state method and was used as an additive to overcome the drawbacks of MgH₂. Interestingly, after adding 10 wt% of BaMnO₃, the initial desorption temperature of MgH₂ decreased to 282 °C, which was 138 °C lower than that of pure MgH₂ and 61 °C lower than that of milled MgH₂. For absorption kinetics, at 250 °C in 2 min, 10 wt% of BaMnO₃-doped MgH₂ absorbed 5.22 wt% of H₂ compared to milled MgH₂ (3.48 wt%). Conversely, the desorption kinetics also demonstrated that 10 wt% of BaMnO₃-doped MgH₂ samples desorbed 5.36 wt% of H₂ at 300 °C within 1 h whereas milled MgH₂ only released less than 0.32 wt% of H₂. The activation energy was lowered by 45 kJ/mol compared to that of MgH₂ after the addition of 10 wt% of BaMnO₃. Further analyzed by using XRD revealed that the formation of Mg_0·9Mn_0·1O, Mn₃O₄ and Ba or Ba-containing enhanced the performance of MgH₂.