Hydrogen trapping in MAX phase Ti3SiC2: Insight from chemical bonding by density functional theory

Understanding hydrogen (H) isotope trapping in materials is essential to optimize the material performance in a nuclear environment for the fabrication of nuclear devices. By using the density functional theory (DFT), herein we have systematically investigated the behaviour of hydrogen in the MAX phase Ti 3 SiC 2 in the presence and absence of a vacancy (V). When a vacancy is generated in a favorable plane for hydrogen accumulating (Si plane), two distinct behavours of hydrogen in the Si plane have been identified by chemical bond analysis, i.e. , the Ti-H and Si-H bonding, which synergistically results in VH 2 complexes prevailing in the host matrix. Different from metals and other ceramics, the trapping mechanism of H in Ti 3 SiC 2 essentially originates from the spatially inhomogeneous distribution of free-charge density and large discrepancy of electronegativity between the host atoms. Our theoretical results offer great insights into the rational design of new high-performance nuclear materials.