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 (H_ads) 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.