All-solid-state mechanochemical synthesis of Cu²⁺-doped MIL-53(Fe) for high-efficient nitrate electroreduction to ammonia

Electrocatalytic nitrate reduction has emerged as a promising strategy for sustainable ammonia synthesis, providing the dual advantage of mitigating nitrate pollution and producing value-added green ammonia. However, enhancing intrinsic catalytic activity and catalytic site accessibility remains a challenge for further improving the performance of nitrate electroreduction to ammonia. Herein, a series of gradient Cu²⁺-doped MIL-53(Fe) electrocatalysts were synthesized via an all-solid-state mechanochemical synthesis method for electrocatalytic nitrate-to-ammonia conversion. MIL-53(Fe)-CuB exhibits a large NH₃production rate of 2391 ± 327<i>μ</i>g h^-1mg_cat^-1at -0.6 V vs RHE and a high Faradaic efficiency of 82.1% ± 1.2% at -0.3 V vs RHE in 1 M KOH with 100 ppm NO₃^-, demonstrating an excellent electrocatalytic performance for nitrate reduction. This work reveals that Cu²⁺-doping in mechanochemically synthesized Fe-metal-organic frameworks (MOFs) boosts nitrate reduction efficiency and selectivity, while broadening research on foreign metal ion anchoring in MOF electrocatalysis.