Electrochemical Charging of MAX Phases and Their Hydrogen Storage Mechanisms

High Resolution Image Download MS PowerPoint Slide 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 Ti 2 AlC and Ti 3 AlC 2, 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, Ti 2 AlC stored ∼60% in intermediate traps and ∼40% in deep traps, while Ti 3 AlC 2 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.