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

Electrochemical nitrate reduction to ammonia (NO3RR) is a promising pathway for nitrogen recycling but remains hindered by complex multistep kinetics and severe competition from the hydrogen evolution reaction. Coupling NO3RR 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-LaSrAgFeCoOx). The structural complexity and abundant oxygen vacancies (Ov) of the LaSrAgFeCoOx synergistically interact with the exsolved Ag NIs, creating spatially and functionally distinct active sites. As a result, the Ag-LaSrAgFeCoOx catalyst achieves high NH4 + 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 NO3 -, while Ov-rich LaSrAgFeCoOx promotes intermediates hydrogenation and NH3 desorption, alongside efficient hydrogen supply. Moreover, the bifunctional Ag-LaSrAgFeCoOx enables energy-efficient NO3RR||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.