From Single Motif to Active Ensembles: Phase-Controlled Co₈ Cluster Catalysis on MoS₂ for Nitrogen Electroreduction

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 MoS₂-directs the structure and electrochemical nitrogen reduction (eNRR) performance of supported Co₈ clusters via machine-learning-potential-accelerated multiscale simulations. On 1T-MoS₂, strong metal-support interactions act as a structural converger, locking Co₈ into a single dominant operando active motif. In contrast, 2H-MoS₂ 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: Co₈N₇H₁₂/2H-MoS₂ hosts a larger population of intrinsically active motifs and delivers an ammonia production rate significantly higher than that of Co₈N₇H₁₄/1T-MoS₂ 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 N₂H₂ 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.