High‐Entropy Effect of Mesoporous Metal Oxides Promotes Tandem Catalysis for Efficient Ammonia Electrosynthesis from Nitrate

Abstract Electrocatalytic nitrate reduction reaction (NO₃⁻RR) in water offers a sustainable alternative for robust electrosynthesis of value‐added ammonia (NH₃) in ambient conditions. However, NO₃⁻RR electrocatalysis generally involves two‐step tandem routes and suffers from sluggish hydrodeoxygenation kinetics, which result in a low ammonia selectivity and yield rate. In this work, it is demonstrated that the high‐entropy effect of mesoporous metal oxides remarkably decreases the energy barrier of the hydrodeoxygenation route and facilitates two‐step tandem electrocatalysis of NO₃⁻RR, which thus promotes selective NH₃ electrosynthesis in an alkaline condition. By comparing a series of high‐entropy mesoporous metal oxides and corresponding metal alloys and monometallic counterparts, high‐entropy mesoporous (CoMnFeNiCu)₃O₄ discloses the highest electrocatalytic performance for efficient NH₃ electrosynthesis from NO₃⁻RR, including remarkable NH₃ Faradaic efficiency of 96.3%, high NH₃ yield rate of 1.83 mmol h⁻¹ mg⁻¹, and excellent recycling stability of 20 cycles, representing one of the best electrocatalysts reported in the past three years. Moreover, cathode NO₃⁻RR performance for selective NH₃ electrosynthesis is enhanced when further coupled with the thermodynamically favorable benzyl alcohol oxidation reaction at the anode. It is expected that the high‐entropy effect opens up a new route to design a library of novel tandem mesoporous metal electrocatalysts for the selective electrosynthesis of various valuable chemicals from wastewater.