Dual-Metal-Site Metal-Organic Frameworks for Oxygen Reduction: The Crucial Role of Environmental Species Covering on the Secondary Site.

Macrocycle-based dual-metal-site metal-organic frameworks emerge as promising catalysts whose activity can be conveniently manipulated via metal node modification. However, how the metal node affects catalysis remains unclear. Herein, using first-principles calculations, we provide new mechanistic insight into dual-metal-site catalysis, where the recently synthesized M 1 -CoOAPc materials (M 1 = Co, Ni, Cu; OAPc = octaaminophthalocyanine) are adopted for demonstration. The modeling results explain experimental measurements of Ni- and Cu-CoOAPc for facilitating oxygen reduction while highlighting a contradiction between the theoretical and experimental activity of Co-CoOAPc. Remarkably, this contradiction is attributed to the inherent H 2 O adsorption on Co nodes, which is usually neglected in dual-metal-site studies. We expand M 1 -CoOAPc with other metal nodes and find that Fe-CoOAPc (involving *H 2 O on the Fe nodes) exhibits a desirable theoretical half-wave potential of 0.82 V, as revealed from constant-potential and microkinetic modeling. This work improves the understanding of dual-metal-site catalysis by uncovering the impact of environmental species covering on the secondary site.