Hydrogen Storage Properties Of LiAlH4 Research Articles

Thermally induced in situ fabrication of TiO2/CN heterojunction dopant for enhancement of hydrogen storage properties of LiAlH4

Herein, a novel TiO2/CN heterojunction material has been prepared by one-step bubble template-assisted calcination to enhance the hydrogen storage capability of LiAlH4. The TEM, XPS and UPS analysis confirm that a heterostructure is formed between TiO2 and g-C3N4 successfully. The experimental findings indicate that the TiO2/CN significantly enhances the dehydrogenation performance of LiAlH4. For instance, the LiAlH4-7 wt% TiO2/CN starts to dehydrogenize at 76 °C (94 °C less than pure LiAlH4) and releases 6.5 wt% H2 at 200 °C. Meanwhile, LiAlH4-7 wt% TiO2/CN releases 4.9 wt% H2 at 120 °C within 50 min. The mechanism analysis illustrates that AlTi3N is formed in situ during ball-milling. And density functional theory (DFT) calculation results reveal that the AlTi3N can weaken the Al-H bonds in LiAlH4 through interfacial charge transfer. Furthermore, the TiO2/CN heterostructure creates an internal electric field that generates an electron-rich layer. As a result, the negative electron layer at one end of the TiO2/CN heterojunction has an increased affinity for H, which enhances the dehydrogenation reaction of LiAlH4. Clearly, both the TiO2/CN heterostructure and AlTi3N contribute to the improvement of the dehydrogenation properties of LiAlH4.

Tailoring the Metallic and Oxide Sites of Pd/C and Ni/C Catalysts for Optimum Hydrogen Oxidation Reaction (HOR) and Durability in Alkaline Media

In recent years, Pd- and Ni-based, or Pd-Ni alloys catalysts for HOR in alkaline electrolytes obtained increasing attention due to their higher durability than Pt-based catalysts. [1-3] However, to prevent passivation in high pH media and maintain active metal/oxide sites, it is necessary to protect the surface of Pd and Ni. It is well documented that different types of carbon cover layers surrounding Ni particles, such as graphite or carbon nanotube, can be beneficial for several applications, e.g. hydrogenation, dehydrogenation, methanol oxidation [4-6], and HOR. Gao et al. reported different degree of graphite coverage-Ni particles of controlled metal/oxide ratio that can enhance the HOR activity of Ni in alkaline electrolytes [7]. In this work, we explore different carbon layer properties, morphology and thickness that cover Pd and Ni particles. Thicker cover layers lead to low HOR activity initially because of the un-balanced metal/oxide sites (the amount of metal sites is higher originally), but can be improved (activated) by voltage pulsing (0.1 - 1.23 V vs. RHE, 3 s each potential, 300 cycles) in 0.1 M KOH, 25°C, Ar gas, without agglomerating the particles (as shown in Figure 1). After full activation, protected Pd and protected Ni were compared with bare Pd and bare Ni (no protecting layers) before and after accelerated stress test (AST) in the potential range of [0.1, 1.23] V vs. RHE. IL-TEM, XRD and XPS techniques show that for protected Pd and Ni, the passivation and degradation happen much slower than for bare Pd and bare Ni (which are immediately deactivated upon AST); also, the proportion of metal or oxide sites can be tailored by different activation procedure, which renders these protected catalysts suitable for long-term alkaline HOR. Figure 1 IL-TEM of Pd C1 (Pd-capped 1) at its initial state vs. post-activation (300 cycles-Ar). Top: 200 k magnified micrographs. Bottom: 500 k magnified micrographs.[1] Lafforgue, C.; Zadick, A.; Dubau, L.; Maillard, F.; Chatenet, M. Selected Review of the Degradation of Pt and Pd-Based Carbon-Supported Electrocatalysts for Alkaline Fuel Cells: Towards Mechanisms of Degradation. Fuel Cells 2018, No. 0, 1–10.[2] Sankar, S.; Anilkumar, G. M.; Tamaki, T.; Yamaguchi, T. Binary Pd−Ni Nanoalloy Particles over Carbon Support with Superior Alkaline Formate Fuel Electrooxidation Performance. ChemCatChem 2019, 11 (19), 4731–4737.[3] Zhao, Y.; Wang, G.; Xiao, L.; Lu, J.; Zhuang, L. Hydrogen Oxidation Reaction on Pd-Ni(OH)2 Composite Electrocatalysts in an Alkaline Electrolyte. ChemistrySelect 2020, 5 (26), 7803–7807. )[4] Ortega-Domínguez, R. A.; Vargas-Villagrán, H.; Peñaloza-Orta, C.; Saavedra-Rubio, K.; Bokhimi, X.; Klimova, T. E. A Facile Method to Increase Metal Dispersion and Hydrogenation Activity of Ni/SBA-15 Catalysts. Fuel 2017, 198, 110–122.[5] Jiao, C.; Sun, L.; Xu, F.; Liu, S. S.; Zhang, J.; Jiang, X.; Yang, L. NiCo Nanoalloy Encapsulated in Graphene Layers for Improving Hydrogen Storage Properties of LiAlH4. Sci. Rep. 2016, 6 (January), 4–11.[6] Tong, X.; Qin, Y.; Guo, X.; Moutanabbir, O.; Ao, X.; Pippel, E.; Zhang, L.; Knez, M. Enhanced Catalytic Activity for Methanol Electro-Oxidation of Uniformly Dispersed Nickel Oxide Nanoparticles-Carbon Nanotube Hybrid Materials. Small 2012, 8 (22), 3390–3395.[7] Yang, Y.; Sun, X.; Han, G.; Liu, X.; Zhang, X.; Sun, Y.; Zhang, M.; Cao, Z.; Sun, Y. Enhanced Electrocatalytic Hydrogen Oxidation on Ni/NiO/C Derived from a Nickel-Based Metal–Organic Framework. Angew. Chemie - Int. Ed. 2019, 58 (31), 10644–10649.[8] Gao, Y.; Peng, H.; Wang, Y.; Wang, G.; Xiao, L.; Lu, J.; Zhuang, L. Improving the Antioxidation Capability of the Ni Catalyst by Carbon Shell Coating for Alkaline Hydrogen Oxidation Reaction. ACS Appl. Mater. Interfaces 2020, 12 (28), 31575–31581. Figure 1

Catalytic effect of SrFe12O19 on the hydrogen storage properties of LiAlH4

The effects of a SrFe12O19 addition on the hydrogen storage properties of LiAlH4 were investigated for the first time, to the best of our knowledge. The addition of the SrFe12O19 show improved dehydrogenation performance compared with that of undoped LiAlH4. In fact, the onset desorption temperatures decreased from 140 °C to 80 °C in the first reaction stage and from 180 °C to 135 °C in the second reaction stage. In terms of the dehydrogenation kinetics, the 10 wt% SrFe12O19-added LiAlH4 sample released approximately 5.54 wt% hydrogen at 130 °C after 20 min desorption, whereas the as-milled LiAlH4 sample released less than 0.3 wt% hydrogen in the same period of time and temperature. Kissinger analysis indicates that the apparent activation energies of the first two dehydrogenation reactions of LiAlH4 are decreased by approximately 27 and 15 kJ/mol, respectively, after the addition of SrFe12O19. It is reasonable to conclude that the formation of an in situ active species of Fe and LiFeO2 and amorphous Sr or Sr-containing phases could play a catalytic role in enhancing the dehydrogenation performance of LiAlH4.

NiCo nanoalloy encapsulated in graphene layers for improving hydrogen storage properties of LiAlH4.

NiCo nanoalloy (4–6 nm) encapsulated in grapheme layers (NiCo@G) has been prepared by thermolysis of a 3D bimetallic complex CoCo[Ni(EDTA)]2·4H2O and successfully employed as a catalyst to improve the dehydrogenation performances of LiAlH4 by solid ball-milling. NiCo@G presents a superior catalytic effect on the dehydrogenation of LiAlH4. For LiAlH4 doped with 1 wt% NiCo@G (LiAlH4-1 wt% NiCo@G), the onset dehydrogenation temperature of LiAlH4 is as low as 43 °C, which is 109 °C lower than that of pristine LiAlH4. 7.3 wt% of hydrogen can be released from LiAlH4-1 wt% NiCo@G at 150 °C within 60 min. The activation energies of LiAlH4 dehydrogenation are extremely reduced by 1 wt% NiCo@G doping.

Improved hydrogen storage properties of LiAlH4 by mechanical milling with TiF3

Dehydrogenation behavior of LiAlH4 (lithium alanate) admixed with TiF3 is investigated by pressure-composition-temperature (PCT), fourier transform infrared spectroscopy (FTIR), X-ray Diffraction (XRD), differential scanning calorimetry (DSC) and temperature programmed desorption (TPD). The TiF3 addition enhances kinetics of LiAlH4 and decreases the decomposition temperature. The LiAlH4-2 mol % TiF3 sample starts to release hydrogen at about 35 °C and the dehydrogenation rate reaches a maximum value at 108.4 °C, compared with 145 °C and 179.9 °C for the as-received LiAlH4. As for the dehydrogenation kinetics, the LiAlH4-2 mol % TiF3 sample releases about 7.0 wt % H2 at 140 °C within 80 min. In comparison, the as-received LiAlH4 sample releases only 0.8 wt % hydrogen under the same conditions. The existence of proposed catalyst, Al3Ti formed in-situ in the process of dehydrogenation, has been confirmed experimentally by XRD measurements. The activation energy of LiAlH4-2 mol % TiF3 composite is deduced to be 66.76 kJ mol−1 and 88.21 kJ mol−1 for the first and second reaction stages of LiAlH4 dehydrogenation.

Enhanced catalytic effects of Co@C additive on dehydrogenation properties of LiAlH4

The catalytic effects of Co@C additive on hydrogen storage properties of LiAlH4 prepared by ball milling have been systematically investigated. The onset desorption temperature of Co@C–LiAlH4 sample is 100.0°C, which is 51°C lower than that of as-received LiAlH4. Isothermal desorption results show that for Co@C–LiAlH4 dehydrogenated at 130°C, 4.58wt% of hydrogen can be released with 180min, which is 3.56wt% higher than that of as-received LiAlH4 under the same conditions. Approximately 7.05wt% of hydrogen is released at 150°C. Through the Kissinger desorption kinetics analyses, the apparent activation energy, Ea, of Co@C–LiAlH4 is calculated as 95.36kJmol−1 H2 and 115.6kJmol−1 H2 for the first two decomposition processes, respectively. It indicates that dehydrogenation kinetics of LiAlH4 matrix considerably improves by doping the Co@C catalyst.

Catalytic nanoconfinement effect of in-situ synthesized Ni-containing mesoporous carbon scaffold (Ni-MCS) on the hydrogen storage properties of LiAlH4

We demonstrate in-situ synthesis of homogeneously dispersed Ni-containing mesoporous carbon scaffold (Ni-MCS) for improving dehydrogenation kinetics of LiAlH4 (hereafter denoted as LAH). LAH was impregnated into Ni-MCS scaffold (LAH confined-Ni-MCS) and also into pure mesoporous carbon scaffold (MCS) (LAH confined-MCS). The XRD patterns of LAH confined in Ni-MCS system indicate its amorphous nature, while 27Al MAS NMR spectroscopy confirmed the nanoconfinement of LAH in the Ni-MCS system. TPD-MS demonstrated the released of H2 at 66 °C for the LAH confined-Ni-MCS system, with 84 °C reduction of the onset desorption temperature (Tonset) as compared to the pure LAH. The H2 desorption from LAH confined-Ni-MCS is about 6.19 wt% H2. This strategy enables the exertion of nanoconfinement, Ni catalyst and compartmentalization effects over the growth of particle size and aggregation, which also significantly contributed to reduce the activation energy (Ea) (39.67 kJ/mol) of the system.

Enhanced hydrogen storage properties of LiAlH4 catalyzed by CoFe2O4 nanoparticles

The catalytic effects of CoFe2O4 nanoparticles on the hydrogen storage properties of LiAlH4 prepared by ball milling were investigated.

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.

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 (TiH2nano) prepared by reactive ball milling is used to dope LiAlH4. It shows superior catalytic effect on the dehydrogenation of LiAlH4 compared to commercial TiH2. TiH2nano-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 TiH2nano-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.

Comparative catalytic effects of NiCl2, TiC and TiN on hydrogen storage properties of LiAlH4

Catalytic effects of NiCl2, TiC and TiN on the dehydrogenation/rehydrogenation characteristics of LiAlH4 were investigated by pressure-content-temperature (PCT), X-ray diffraction (XRD), differential scanning calorimatory (DSC), and field emission scanning electron microscopy (FESEM). The doped samples exhibit dehydrogenation at much lower temperatures. Doping with NiCl2, TiC and TiN induce a decrease in the decomposition of first step by about 50–65 °C compared to that of as received LiAlH4. Also, amount of hydrogen release is significantly higher for TiC additions than that of samples doped with TiN and NiCl2. Isothermal desorption results at 125 °C reveal that dehydrating rate of doped alanate is much faster than that of pure LiAlH4. TiC, TiN and NiCl2 dopants show the reabsorption of about 1.9 wt.%, 1.3 wt.%, and 1.1 wt.%, respectively. XRD and FESEM analyses suggest that both TiC and TiN are stable during the ball milling as well as the dehydrogenation processes. On the contrary, NiCl2 reacts and causes the partial decomposition of Li alanate during the ball milling process.