Generalizable Mechanochemical Impact of Curvature Governing Stability and Reactivity at Catalytic Sites on Rippled Supports

Abstract

Graphene is inherently prone to forming ripples and curved regions, both with and without defects, which modify its local geometry and, consequently, its electronic structure. Such curvature effects become particularly important when graphene serves as a support for atomically dispersed single-atom catalytic sites (M-N-C), which are key motifs for small-molecule activation. These sites can be regarded as defect structures within a two-dimensional (2D) framework; however, the role of curvature as a vector descriptor-capturing both the magnitude and the direction (sign) of curvature-remains largely unexplored in reactivity analysis. Here, we investigate how the sign of curvature impacts the stability, electronic structure, and adsorption properties of M-N-C sites using first-principles density functional theory (DFT) calculations encompassing 3d, 4d, and 5d transition-metal centers. We find that curvature modulates the thermodynamic stability of single-atom sites, with larger metal centers being preferentially stabilized in regions of higher curvature. Furthermore, curvature modulates key aspects of chemical bonding, including covalency and ionicity, as demonstrated using H adsorption as a model case. Curvature serves as a control parameter for tuning the M-H bonding strength, with the effect being most pronounced for early transition metals. CO2 activation is then examined as a representative example of small-molecule activation under curvature, revealing that the nature of curvature can drastically modify the activation mechanism at a given metal center. Notably, curvature enhances CO2 adsorption and activation even for metals that are inactive on flat surfaces. Because ripples are intrinsic to 2D materials and can also be engineered through external stimuli or mechanochemical deformation, these findings demonstrate that exploiting curvature as a vector descriptor in chemical space enables new forms of reactivity inaccessible on planar surfaces.