Entropy-Engineered Catalysts for Electrochemical Nitrate Reduction to Ammonia

Medium-entropy alloys (MEAs) and high-entropy alloys (HEAs) have recently emerged as promising electrocatalysts, owing to their compositional complexity, electronic tunability, and configurational entropy. They offer a diverse array of active sites, favorable adsorption energies, and enhanced structural stability, enabling efficient and selective multielectron nitrate reduction. Herein, we critically examine the recent advances in MEA/HEA-based electrocatalysts for nitrate reduction reaction (NO₃RR), detailing their synthetic strategies, phase behaviors, structure and property relationships, and mechanistic pathways. Mechanistic insights into NO₃RR, with emphasis on proton-coupled electron transfer, intermediate stabilization, and hydrogen evolution suppression, are also discussed. A comparative assessment with monometallic and bimetallic systems is presented to highlight the advantages conferred by entropy-driven design. Moreover, recent developments in operando characterization, density functional theory modeling, and alloy microstructure optimization are reviewed to provide a comprehensive understanding of catalyst behavior. This work outlines key challenges, such as atomic-scale surface control and long-term durability, and proposes future directions to advance entropy-engineered catalysts in sustainable nitrogen chemistry. The review bridges the gap between fundamental alloy theory and practical applications, positioning MEAs and HEAs as next-generation electrocatalysts for green NH₃ synthesis.