MOF‐on‐MOF Heterostructured Electrocatalysts for Efficient Nitrate Reduction to Ammonia.

Electrocatalytic nitrate reduction reaction (NO3−RR) is an important route for sustainable NH3 synthesis and environmental remediation. Metal–organic frameworks (MOFs) are one family of promising NO3−RR electrocatalysts, however, there is plenty of room to improve in their performance, calling for new design principles. Herein, a MOF‐on‐MOF heterostructured electrocatalyst with interfacial dual active sites and build‐in electric field is fabricated for efficient NO3−RR to NH3 production. By growing Co‐HHTP (HHTP=2,3,6,7,10,11‐hexahydroxytriphenylene) nanorods on Ni‐BDC (BDC=1,4‐benzenedicarboxylate) nanosheets, experimental and theoretical investigations demonstrate the formation of Ni−O−Co bonds at the interface of MOF‐on‐MOF heterostructure, leading to dual active sites tailed for NO3−RR. The Ni sites facilitate the adsorption and activation of NO3−, while the Co sites boost the H2O decomposition to supply active hydrogen (Hads) for N‐containing intermediates hydrogenation on adjacent Ni sites, cooperatively reducing the energy barriers of NO3−RR process. Together with the accelerated electron transfer enabled by built‐in electric field, remarkable NO3−RR performance is achieved with an NH3 yield rate of 11.46 mg h−1 cm−2 and a Faradaic efficiency of 98.4 %, outperforming most reported MOF‐based electrocatalysts. This work provides new insights into the design of high‐performance NO3−RR electrocatalysts. [ABSTRACT FROM AUTHOR]