Decoupling Kinetically Coupled Steps via Hierarchical Relay Catalysis on High‐Entropy Alloy for Efficient Ammonia Decomposition

Ammonia (NH 3 ) is a promising hydrogen carrier owing to its high gravimetric hydrogen storage density (17.6 wt%), but its practical utilization is hindered by sluggish decomposition kinetics at moderate temperatures. For commonly used Ru‐based catalysts, the reaction remains constrained by kinetically coupled elementary steps, including both N‐H bond activation and inhibited H desorption. Herein, we propose a hierarchical relay catalysis strategy enabled by a RuNiCoFeMo high‐entropy‐alloy (HEA) catalyst, wherein distinct metallic centers are rationally integrated to regulate individual elementary steps within a single catalytic framework. Specifically, NiCoFe sites preferentially promote sequential N‐H bond scission, while Mo incorporation electronically modulates the alloy to weaken metal‐H interactions and suppress hydrogen poisoning, thereby breaking scaling constraints across multiple elementary steps. Consequently, the optimized catalyst exhibits ca. 56% and 54% higher NH 3 and H 2 reaction orders relative to the monometallic Ru, respectively, indicating enhanced NH 3 activation and alleviated hydrogen poisoning. These kinetic benefits translate into a threefold increase in NH 3 conversion and H 2 production, reaching ca. 80% NH 3 conversion at 450°C, which is among the highest activities reported for Ru‐based catalysts. This work provides a general design principle for catalyst design in complex multistep reactions beyond NH 3 decomposition.