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Figure 2. Hydrogen embrittlement phenomena and mechanisms. (A) Schematic illustration of hydrogen trapping sites within materials at the atomic level. (B) Diagram outlining the HEDE mechanism, highlighting the tensile separation of atoms due to weakened interatomic bonds influenced by hydrogen in the lattice, adsorbed on surfaces, and present at interfaces between particles and the matrix. (C) Diagram depicting the HELP mechanism, characterized by localized plastic deformation and microvoid coalescence in areas of high hydrogen concentration. (D) Diagram illustrating the AIDE mechanism, which facilitates crack propagation via alternate-slip movements from crack tips, enhancing crack and void merging in the plastic zone. Reproduced with permission^[20], Copyright 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd.