Solid-State Hydrogen Storage Properties of Ti–V–Nb–Cr High-Entropy Alloys and the Associated Effects of Transitional Metals (M = Mn, Fe, Ni)

Abstract

Recently, high-entropy alloys (HEAs) designed by the concepts of unique entropy-stabilized mechanisms, started to attract widespread interests for their hydrogen storage properties. HEAs with body-centered cubic (BCC) structures present a high potential for hydrogen storage due to the high hydrogen-to-metal ratio (up to H/M = 2) and vastness of compositions. Although many studies reported rapid absorption kinetics, the investigation of hydrogen desorption is missing, especially in BCC HEAs. We have investigated the crystal structure, microstructure and hydrogen storage performance of a series of HEAs in the Ti–V–Nb–Cr system. Three types of TiVCrNb HEAs (Ti4V3NbCr2, Ti3V3Nb2Cr2, Ti2V3Nb3Cr2) with close atomic radii and different valence electron concentrations (VECs) were designed with single BCC phase by CALPHAD method. The three alloys with fast hydrogen absorption kinetics reach the H/M ratio up to 2. Particularly, Ti4V3NbCr2 alloy shows the hydrogen storage capacity of 3.7 wt%, higher than other HEAs ever reported. The dehydrogenation activation energy of HEAs’ hydride has been proved to decrease with decreasing VEC, which may be due to the weakening of alloy atom and H atom. Moreover, Ti4V3NbCr2M (M = Mn, Fe, Ni) alloys were also synthesized to destabilize hydrides. The addition of Mn, Fe and Ni lead to precipitation of Laves phase, however, the kinetics did not improve further because of their own excellent hydrogen absorption. With increasing the content of Laves phase, there appear more pathways for hydrogen desorption so that the hydrides are more easily dissociated, which may provide new insights into how to achieve hydrogen desorption in BCC HEAs at room temperature.

A review on BCC-structured high-entropy alloys for hydrogen storage

“…Moreover, Edalati et al (2020) suggested that the rapid hydrogen absorption/desorption performance can be obtained at room temperature when the VEC is greater than 6.4. In our work (Cheng et al, 2022), TiVNbCr alloys with different VECs were designed and it was discovered that they possess a hydrogen capacity of H/M = 2 for a widely range of compositions, reaching a high Comparison of the positions of high entropy alloys and conventional alloys on the isothermal cross section of the ternary phase diagram (A) (Pradeep et al, 2015); the relative division of hydrogen-absorbing (in red) and non-hydrogen-absorbing (in blue) elements in the periodic table of elements according to the enthalpy of formation of M-H metal hydrides (B) (Latroche et al, 2021).…”

“…Strozi et al (2022) designed compositions with different phase structures (BCC and C15 Laves phases) in the TiVNbCr system through the CALPHAD method, and excellent prediction accuracy was demonstrated by X-ray diffraction (XRD) for the different phase structures. Following the same strategy, we designed three compositions of TiVNbCr system with BCC single phase by CALPHAD approach, and the XRD experiments demonstrated the phase diagram prediction with high accuracy (Cheng et al, 2022). As the application demands increase, the design approach to theoretical calculations is extended.…”

“…Wang (2009) reported that the VAM method is more favourable to form the BCC structure and to maintain the hydrogen storage capacity of the alloy. The VAM method has also been used in several of our works to synthesize alloys that maintain a good single-phase structure (the alloy structure is presented in Figure 4A) (Cheng et al, 2022). Based on the above advantages, VAM has become a more popular synthesis method for BCC HEAs for hydrogen storage.…”

“…XRD patterns of the TiVNbCr system alloy synthesized by the VAM method (A) (Cheng et al, 2022); and XRD patterns of Mg 12 Al 11 Ti 33 Mn 11 Nb 33 HEA synthesized by the HEBM method (B) (Strozi et al, 2021a).…”

Large Destabilization of (TiVNb)-Based Hydrides via (Al, Mo) Addition: Insights from Experiments and Data-Driven Models

“…8,16 A number of HEAs with a bcc structure possess outstanding volumetric hydrogen capacities, as reported for TiVZrNbHf, 9 TiVZrNbHf 0.5 17 TiZrNbHfTa, 18 and Ti 4 V 3 NbCr 2 . 19 The inclusion of lightweight elements (such as Mg, Al) to improve gravimetric capacities has also been explored. 20 For example, Mg 35 Al 15 Ti 25 V 10 Zn 15 achieves a high capacity of 2.3−2.7 wt % depending on the method of synthesis (arc melting or reactive ball milling) and forms a mixture of hydrides with desorption temperatures above 300 °C.…”