In‐Situ Exsolving Silver Nano‐islands on High‐Entropy Perovskites for Energy‐Efficient Coupled Nitrate Reduction and Sulfide Oxidation

ABSTRACT Electrochemical nitrate reduction to ammonia (NO 3 RR) is a promising pathway for nitrogen recycling but remains hindered by complex multistep kinetics and severe competition from the hydrogen evolution reaction. Coupling NO 3 RR with the sulfide oxidation reaction (SOR) offers an energy‐efficient alternative by simultaneously enabling dual‐pollutant remediation with value‐added products. Herein, we report an in situ exsolution strategy to construct a tandem electrocatalyst composed of exsolved Ag nano‐islands (NIs) anchored on a high‐entropy perovskite oxide matrix (Ag‐LaSrAgFeCoO x ). The structural complexity and abundant oxygen vacancies (O v ) of the LaSrAgFeCoO x synergistically interact with the exsolved Ag NIs, creating spatially and functionally distinct active sites. As a result, the Ag‐LaSrAgFeCoO x catalyst achieves high NH 4 + Faradaic efficiency of 97.6% and yield rate of 0.35 mmol h– 1 cm −2 . In situ characterization and theoretical calculations reveal a relay catalytic mechanism in which Ag sites of Ag NIs preferentially activate NO 3 – , while O v ‐rich LaSrAgFeCoO x promotes intermediates hydrogenation and NH 3 desorption, alongside efficient hydrogen supply. Moreover, the bifunctional Ag‐LaSrAgFeCoO x enables energy‐efficient NO 3 RR||SOR coupling, delivering a positive open‐circuit potential of 557 mV and stable co‐production of ammonia and sulfur. This work highlights high‐entropy materials as a powerful platform for tandem electrocatalysis in complex coupled reactions.