The origin of anomalous hydrogen occupation in high entropy alloys

Jutao Hu; Jinjing Zhang; Menglu Li; Sa Zhang; Haiyan Xiao; Lei Xie; Guangai Sun; Huahai Shen; Xiaosong Zhou; Xiaoqing Li; Pengcheng Li; Jianwei Zhang; Levente Vitos; Xiaotao Zu

doi:10.1039/D1TA10649J

The origin of anomalous hydrogen occupation in high entropy alloys†

Jutao Hu,^a Jinjing Zhang,^a Menglu Li,^a Sa Zhang,^a Haiyan Xiao,

*^a Lei Xie,^b Guangai Sun,^b Huahai Shen,*^b Xiaosong Zhou,^b Xiaoqing Li,*^c Pengcheng Li,^a Jianwei Zhang,^a Levente Vitos

^c and Xiaotao Zu^a

Author affiliations

* Corresponding authors

^a School of Physics, University of Electronic Science and Technology of China, Chengdu, China
E-mail: hyxiao@uestc.edu.cn

^b Institute of Nuclear Physics and Chemistry, China Academy of Engineering Physics, Mianyang, China
E-mail: huahaishen@caep.cn

^c Department of Materials Science and Engineering, KTH-Royal Institute of Technology, Stockholm, Sweden
E-mail: xiaoqli@kth.se

Abstract

Metal hydrogen storage materials have been the focus of intensive research in the field of hydrogen-based economy. An outstanding question is that the number of hydrogen atoms accommodated in metal hydrides is generally much below the number of interstices, which limits their hydrogen storage capacities. Unlike traditional FCC metal hydrides where hydrogen can only occupy tetrahedral interstices, this study demonstrates that hydrogen can also occupy octahedral interstices in FCC high entropy alloy (HEA) hydrides, which leads to the violation of the Switendick criterion. For Ti₂₅V₂₅Nb₂₅Ta₂₅ and Ti₂₅V₂₅Nb₂₅Zr₂₅ HEAs, nearly 20% and 17.5% of octahedral interstices can be occupied by hydrogen, respectively. The anomalous hydrogen occupation mainly originates from the intrinsic electron delocalization between hydrogen atoms in HEA hydrides, which presents a sharp contrast to traditional metal hydrides. Such electron delocalization decreases repulsive interactions between hydrogens and promotes the electron localization at octahedral interstices. Additionally, this study reveals that hydrogen occupation at octahedral interstices enhances the structural disordering and decreases the thermal stability of HEA hydrides, which will be beneficial to reduce the dehydrogenation temperature. The presented results may provide a new strategy for the design of high-density storage materials.

Journal of Materials Chemistry A

The origin of anomalous hydrogen occupation in high entropy alloys†

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The origin of anomalous hydrogen occupation in high entropy alloys

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