Hydrogen Absorption Reactions of Hydrogen Storage Alloy LaNi5 under High Pressure

Abstract

Hydrogen can be stored in the interstitial sites of the lattices of intermetallic compounds. To date, intermetallic compound LaNi5 or related LaNi5-based alloys are known to be practical hydrogen storage materials owing to their higher volumetric hydrogen densities, making them a compact hydrogen storage method and allowing stable reversible hydrogen absorption and desorption reactions to take place at room temperature below 1.0 MPa. By contrast, gravimetric hydrogen density is required for key improvements (e.g., gravimetric hydrogen density of LaNi5: 1.38 mass%). Although hydrogen storage materials have typically been evaluated for their hydrogen storage properties below 10 MPa, reactions between hydrogen and materials can be facilitated above 1 GPa because the chemical potential of hydrogen dramatically increases at a higher pressure. This indicates that high-pressure experiments above 1 GPa could clarify the latent hydrogen absorption reactions below 10 MPa and potentially explore new hydride phases. In this study, we investigated the hydrogen absorption reaction of LaNi5 above 1 GPa at room temperature to understand their potential hydrogen storage capacities. The high-pressure experiments on LaNi5 with and without an internal hydrogen source (BH3NH3) were performed using a multi-anvil-type high-pressure apparatus, and the reactions were observed using in situ synchrotron radiation X-ray diffraction with an energy dispersive method. The results showed that 2.07 mass% hydrogen was absorbed by LaNi5 at 6 GPa. Considering the unit cell volume expansion, the estimated hydrogen storage capacity could be 1.5 times higher than that obtained from hydrogen absorption reaction below 1.0 MPa at 303 K. Thus, 33% of the available interstitial sites in LaNi5 remained unoccupied by hydrogen atoms under conventional conditions. Although the hydrogen-absorbed LaNi5Hx (x < 9) was maintained below 573 K at 10 GPa, LaNi5Hx began decomposing into NiH, and the formation of a new phase was observed at 873 K and 10 GPa. The new phase was indexed to a hexagonal or trigonal unit cell with a ≈ 4.44 Å and c ≈ 8.44 Å. Further, the newly-formed phase was speculated to be a new hydride phase because the Bragg peak positions and unit cell parameters were inconsistent with those reported for the La-Ni intermetallic compounds and La-Ni hydride phases.

Microstructure and First Hydrogenation Properties of Ti30V60Mn(10−x)Crx (x = 0, 3.3, 6.6, 10) + 4 wt.% Zr

“…For hydrogen storage applications, metal hydrides have the benefit of storing hydrogen with high volumetric storage density, low cost [1] and safety [2]. Several types of intermetallic compounds have been investigated for hydrogen storage: AB 2 [3], AB 5 [4], LaNi 5 [5,6] TiFe [7,8], and ZrV 2 [9]. Mg-based alloys have a large capacity, but their temperature of operation is usually too high for most practical applications [10][11][12][13].…”

Research Progress and Application Prospects of Solid-State Hydrogen Storage Technology

“…(1) AB 5 -type metal hydrides, such as LaNi 5 [65,66]. Their hydrogen absorption platform pressure is moderate (0.1-0.3 MPa), and they can release hydrogen at room temperature, but they are expensive and the cost is too high for large-scale hydrogen storage.…”

Physical Analysis and Mathematical Modeling of the Hydrogen Storage Process in the MmNi4.2Mn0.8 Compound

“…Thus, the MmNi 5 compound has demonstrated intriguing hydrogen storage characteristics, such as straightforward activation [42], elevated stability in the electrode potential [40], and a significant hydrogen storage capacity at room temperature, reaching 1.5% Wt [43].However, the MmNi 5 compound has an equilibrium pressure of up to 30 bar [44]. This is a significantly higher value than, for instance, the equilibrium pressure of LaNi 5 , which is limited to 2 bar [45].Given that battery cells clearly operate at atmospheric pressures [46], this suggests a challenging engineering design for gas hydrogen storage, which was totally unworkable in MmNi 5 to be utilized as the anode in a Ni-MH battery cell. In addition, despite the fact that MmNi 5 is highly desirable for stationary applications, there are certain inherent limitations that make it impractical to use.…”