| Abstract: | 氫能被認為是最有前途的清潔和可再生替代能源，這是由於其高能量密度、低碳排放和豐富的資源。然而，實現氫能經濟的一個挑戰在於氫氣的有效儲存。與高壓氣態氫和液態氫儲存技術相比，固態氫儲存具有相對較高的儲氫容量和能源效率、較低的成本以及更高的安全性。在過去二十年中，高熵合金（HEAs）的出現為有效儲存氫氣提供了一種有前景的方法，這是由於其嚴重的晶格扭曲和混合效應。特別是合金和成分設計以及微結構工程的無限可能性，使其成為在不同應用中具有價值的儲氫候選材料。本研究探討了使用新穎高熵合金進行氫氣儲存的概念。
本研究的主要重點是研究通過氣體霧化法和真空電弧熔煉製造的Ti42Zr35Ta3Si5Co12.5Sn2.5 HEA的儲氫特性。此外，旨在通過利用鈦-釩為基礎來重新調整此HEA的成分以優化其儲氫性能。最初的HEA設計是基於熱力學考量，如混合焓（ΔHmix）、混合熵（ΔSmix）和晶格扭曲度（δ）、價電子濃度（VEC），以及元素與氫的親和力。使用電子探針顯微分析儀（EPMA）確認了表面元素分佈和表面形貌。隨後，使用X射線繞射（XRD）和穿透式電子顯微鏡（TEM）檢查了HEAs在吸氫前後的晶體結構和相變化。熱重分析（TGA）和差示掃描量熱法（DSC）用於確定材料的脫氫溫度和脫氫量。最後，使用Sieverts裝置研究了兩種HEAs的儲氫行為，包括壓力-組成-溫度（PCT）曲線和動力學曲線。此外，還在澳大利亞核子科技組織（ANSTO）進行了高解析中子粉末繞射（HRNPD），以研究氫氣儲存位置和晶格變化。
研究發現，多相Ti42Zr35Ta3Si5Co12.5Sn2.5 HEA在400°C和0.00001 bar氫充壓下達到了0.6 wt.%的儲氫容量，在45 bar達到了最大2.15 wt.%。然而，其完全脫氫溫度高達800°C，使其不適合正常操作條件。通過引入釩來降低吸氫溫度並利用鉬和鉻作為體心立方（BCC）穩定劑，成功設計出單相BCC Ti36V11Ta16Mo21Cr16 HEA。這一改進有效降低了吸氫溫度和壓力。Ti36V11Ta16Mo21Cr16在室溫下0.00001 bar壓力下儲氫容量為0.7 wt.%，在36 bar達到最大1.9 wt.%的吸氫量，其完全脫氫溫度僅為500°C。兩種材料均可在10分鐘內達到最大儲氫容量，材料成本僅為文獻中TiZrVNbHf HEA報告成本的四分之一。這項研究證實了BCC HEA結構對儲氫的有效性，並確定了一種低成本的HEA用於此目的。結果表明，合金設計可以提高儲氫性能，證實了其他研究中氫氣可以在非常低的壓力下被HEAs吸收，從而推動了作為可持續綠色能源解決方案之一的固態儲氫材料的發展，可能在未來取代化石燃料並減緩全球暖化。
;Hydrogen energy is considered as the most promising clean and renewable alternative energy source, owing to its high energy density, low carbon emissions, and abundance. However, one of the challenges in the realization of a hydrogen economy lies upon the effective storage of hydrogen. As compared with the pressurized gaseous hydrogen and liquid hydrogen storage techniques, solid-state hydrogen storage offers advantages such as relatively higher hydrogen storage capacity and energy efficiency, lower costs, and increased safety. The emergence of high-entropy alloys (HEAs) in the past two decades has provided a promising means to store hydrogen effectively, owing to their severe lattice distortion and cocktail effects. In particular, the unlimited possibilities of the alloy and composition designs, as well as microstructure engineering, offer very attractive approaches for them to be valuable candidates for hydrogen storage in different applications. The concept of using novel high-entropy alloys for hydrogen storage is explored in this study.
The main focus of this study has been to investigate the low-pressure hydrogen storage properties of Ti42Zr35Ta3Si5Co12.5Sn2.5 HEA fabricated via atomization process and vacuum arc melting process. Additionally, it aims to optimize hydrogen storage performance by utilizing Ti-V as a base to readjust the composition of this HEA. Initially, HEA design was carried out based on thermodynamic considerations, such as mixing enthalpy (ΔHmix), mixing entropy (ΔSmix), and the degree of lattice distortion (δ), valence electron concentration (VEC), as well as the affinity of the elements with hydrogen. The surface element distribution and surface morphology were confirmed using Electron Probe Microanalyzer (EPMA). Subsequently, X-Ray Diffraction (XRD) and Transmission Electron Microscope (TEM) were employed to examine the crystalline structures and phase transformations of the HEAs before and after hydrogen absorption. Thermogravimetric Analysis (TGA) and Differential Scanning Calorimetry (DSC) were utilized to determine the dehydrogenation temperature and melting point of the materials. Finally, the hydrogen storage behavior of the two types of HEAs, including Pressure-Composition Temperature (PCT) curves and kinetic curves, was investigated using a Sieverts apparatus. Furthermore, High Resolution Neutron Powder Diffraction (HRNPD) testing at the Australian Nuclear Science and Technology Organization (ANSTO) was performed to study the hydrogen storage positions and lattice changes.
It was found here that the multiphase Ti42Zr35Ta3Si5Co12.5Sn2.5 HEA achieved a hydrogen storage capacity of 0.6 wt.% at 400°C and 0.00001 bar of hydrogen charging pressure, reaching a maximum of 2.15 wt.% at 45 bar. However, its complete dehydrogenation temperature was as high as 800°C, rendering it unsuitable for normal operation conditions. By introducing V to reduce hydrogen absorption temperature and utilizing Mo and Cr as BCC stabilizers, a single-phase BCC Ti36V11Ta16Mo21Cr16 HEA has been successfully designed. The modification effectively lowers both hydrogen absorption temperature and pressure. The Ti36V11Ta16Mo21Cr16 exhibited a hydrogen storage capacity of 0.7 wt.% at room temperature, under a pressure of 0.00001 bar; with a maximum of 1.9 wt.% of hydrogen uptake achieved at only 36 bar, and its complete dehydrogenation temperature is only 500°C. Both materials can reach maximum hydrogen storage capacity within 10 minutes, with material costs only about a quarter of those reported for the HEA like TiZrVNbHf in the literature. This study has confirmed that the BCC HEA structure is effective for hydrogen storage and has identified a low-cost HEA for this purpose. The results demonstrate that alloying design can enhance hydrogen storage properties, corroborating other research that hydrogen can be absorbed by HEAs at very low pressures, thus promoting a solid-state hydrogen storage material which serves as one of the sustainable green energy solutions to replace fossil fuels and potentially reduce global warming in the future. |
