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

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.