Hydrogen Transport Between Layers of Transition Metal‐Dichalcogenides

Abstract Hydrogen is a crucial source of green energy and is extensively studied for its potential usage in fuel cells. The advent of 2D crystals (2DCs) has taken hydrogen research to new heights, enabling it to tunnel through layers of 2DCs or be transported within voids between the layers, as demonstrated in recent experiments by Geim's group. In this study, it investigates how the composition and stacking of transition‐metal dichalcogenide (TMDC) layers influence the transport and self‐diffusion coefficients (D) of hydrogen atoms using well‐tempered metadynamics (WTMetaD) simulations. The findings show that modifying either the transition metal or the chalcogen atoms significantly affects the free energy barriers (ΔF) and, consequently, the self‐diffusion of hydrogen atoms between the 2DC layers. In the polytype (2H stacking), MoSe₂ exhibits the lowest ΔF, while WS₂ has the highest, resulting in the largest D for the former system. Additionally, hydrogen atoms inside the (or 3R) polytype encounter more than twice lower energy barriers and, thus, much higher diffusivity compared to those within the most stable stacking. These findings are particularly significant when investigating twisted layers or homo‐ or heterostructures, as different stacking areas may dominate over others, potentially leading to directional transport and interesting materials for ion or atom sieving.