From Single Motif to Active Ensembles: Phase‐Controlled Co ₈ Cluster Catalysis on MoS ₂ for Nitrogen Electroreduction

Abstract

ABSTRACT Atomic‐scale metal clusters, which bridge the gap between nanoparticles and single‐atom catalysts, show pronounced structure‐sensitive reactivity that is strongly governed by the support. Here, we reveal that the crystal phase of a two‐dimensional support—metallic 1T versus semiconducting 2H MoS 2 —directs the structure and electrochemical nitrogen reduction (eNRR) performance of supported Co 8 clusters via machine‐learning‐potential‐accelerated multiscale simulations. On 1T‐MoS 2 , strong metal–support interactions act as a structural converger, locking Co 8 into a single dominant operando active motif. In contrast, 2H‐MoS 2 behaves as a structural diverger, stabilizing a thermodynamically broad ensemble of active motifs under reaction conditions. This phase‐controlled structural diversity translates directly into a function: Co 8 N 7 H 12 /2H‐MoS 2 hosts a larger population of intrinsically active motifs and delivers an ammonia production rate significantly higher than that of Co 8 N 7 H 14 /1T‐MoS 2 while concurrently suppressing hydrogen evolution. Electronic structure analysis identified the total Bader charge of the cluster across different exposed active sites as a key descriptor that was exponentially correlated with the N 2 H 2 hydrogenation barrier and turnover frequency. These findings establish a crystal phase–structure–charge–function causal chain and highlight support phase engineering—specifically, the deliberate promotion of structural diversity—as a general strategy that can be extended to other catalytic reactions to increase activity.