Sign of mechanochemical curvature governing O2 activation mechanisms and reactivity on rippled supports

Abstract

Two-dimensional (2D) materials are inherently prone to forming ripples and wrinkles that create regions of nonzero curvature – a mechanochemical landscape arising from intrinsic deformation – thereby modulating their electronic structure and a range of associated properties. Such curvature effects have implications for stability, quantum processes, and adsorption phenomena. The influence of curvature—treated as a vector descriptor distinguishing positive and negative curvature—on reactivity remains underexplored, particularly in the context of small-molecule activation and multistep catalytic reactions. Here, we investigate rippled N-doped graphene and quantify how curvature, viewed as a local mechanochemical deformation, modulates O₂ reactivity on single-atom sites, denoted as M–N–C (M = Fe, Co, Mn, Pt), using density functional theory. We find that the sign of curvature determines the O₂ activation mode: for Mn and Fe, negatively curved regions (mountain-shaped) favor an η² side-on configuration, whereas positively curved regions (valley-shaped) promote an η¹ end-on mode. In contrast, Co and Pt exhibit only curvature-independent η¹ binding. The η² mode observed for Fe and Mn resembles molecular O₂ adducts in transition-metal complexes. Curvature-dependent charge transfer enhances electron donation at negatively curved sites, facilitating O₂ activation. We establish curvature-resolved scaling relations for oxygen reduction reaction (ORR) intermediates (OOH, O, and OH), highlighting where the global linear relationships remain valid and where they break down when curvature is introduced as a geometric variable. The sign of curvature also modulates ORR overpotentials: positive curvature regions yield lower overpotentials, whereas negative curvature sites lead to higher values for Fe and Mn. Consequently, we predict that negatively curved, mountain-like sites can be engineered for O-atom transfer reactions to organic substrates, which compete with ORR under electrochemical conditions. Finally, we show that variable curvature further influences the overpotential by enabling different ORR steps at varying curvatures on a corrugated surface. Overall, curvature can be harnessed to enable distinct reactivity from identical catalytic motifs, underscoring the importance of incorporating dynamic curvature effects in future theoretical and experimental studies.