Department of Engineering Science and Mechanics, College of Engineering, Shibaura Institute of Technology, Tokyo 135-8548, Japan.
Quantum Beam Science Research Directorate, National Institutes for Quantum Science and Technology, Sayo 679-5148, Japan.
Molecules. 2023 Jan 27;28(3):1256. doi: 10.3390/molecules28031256.
Hydrogen can be stored in the interstitial sites of the lattices of intermetallic compounds. To date, intermetallic compound LaNi or related LaNi-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 LaNi: 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 LaNi above 1 GPa at room temperature to understand their potential hydrogen storage capacities. The high-pressure experiments on LaNi with and without an internal hydrogen source (BHNH) 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 LaNi 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 LaNi remained unoccupied by hydrogen atoms under conventional conditions. Although the hydrogen-absorbed LaNiH (x < 9) was maintained below 573 K at 10 GPa, LaNiH 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.
氢可以储存在金属间化合物的晶格间隙中。迄今为止，由于具有较高的体积氢密度，金属间化合物 LaNi 或相关的 LaNi 基合金被认为是实用的储氢材料，这使得它们成为一种紧凑的储氢方法，并允许在室温下低于 1.0 MPa 的稳定可逆吸氢和放氢反应发生。相比之下，需要提高重量氢密度（例如，LaNi 的重量氢密度为 1.38 质量%）。虽然通常在 10 MPa 以下评估储氢材料的储氢性能，但在 1 GPa 以上，由于氢的化学势在更高压力下急剧增加，氢与材料之间的反应可以得到促进。这表明，在 1 GPa 以上的高压实验可以澄清 10 MPa 以下的潜在吸氢反应，并有可能探索新的氢化物相。在这项研究中，我们在室温下研究了 LaNi 在 1 GPa 以上的吸氢反应，以了解其潜在的储氢能力。使用多砧式高压装置对具有和不具有内部氢源（BHNH）的 LaNi 进行了高压实验，并使用同步辐射 X 射线衍射和能量色散法原位观察反应。结果表明，LaNi 在 6 GPa 时吸收了 2.07 质量%的氢。考虑到单位晶胞体积的膨胀，估计的储氢容量可能是在 303 K 时在 1.0 MPa 以下的吸氢反应获得的储氢容量的 1.5 倍。因此，在常规条件下，LaNi 中的可用间隙位有 33%没有被氢原子占据。尽管在 10 GPa 下，氢吸收的 LaNiH（x < 9）在低于 573 K 时得以保持，但 LaNiH 开始分解为 NiH，并且在 873 K 和 10 GPa 时观察到新相的形成。新相的晶胞参数索引为 a ≈ 4.44 Å 和 c ≈ 8.44 Å 的六方或三角晶系。此外，由于布拉格峰位置和晶胞参数与报道的 La-Ni 金属间化合物和 La-Ni 氢化物相不一致，因此推测新形成的相是一种新的氢化物相。
