MAX phases, layered ternary transition metal carbides/nitrides, are proposed as solid-state hydrogen storage materials offering tunable intrinsic trapping sites owing to their unique atomically layered structure; however, experimental validation remains limited. Here, we present a systematic investigation of electrochemical hydrogen charging in Ti2AlC and Ti3AlC2, revealing that the hydrogen storage behavior correlates to the different ratios of metal/carbide layers. Thermal desorption spectroscopy (TDS) and cyclic voltammetry (CV) measurements revealed two distinct hydrogen desorption peaks, associated with intermediate and deep trapping sites. Notably, Ti2AlC stored ∼60% in intermediate traps and ∼40% in deep traps, while Ti3AlC2 showed the opposite trend. Density functional theory (DFT) calculations verify that the intermediate and deep trapping sites correspond to interstitials in the Ti–Al layer and carbon vacancies in the Ti–C layer, respectively. These findings provide insight into the layered-dependent hydrogen trapping, retention, and release in MAX phases, opening new pathways toward trap-engineered hydrogen storage in layered materials.
Miyar et al. (Tue,) studied this question.