Tuning Main Group Element-based Metal-Organic Framework to Boost Electrocatalytic Nitrogen Reduction Under Ambient Conditions.

Main group element-based materials are emerging catalysts for ammonia (NH 3 ) production via a sustainable electrochemical nitrogen reduction reaction (N 2 RR) pathway under ambient conditions. However, their N 2 RR performances are less explored due to the limited active behavior and unclear mechanism. Here, an aluminum-based defective metal-organic framework (MOF), aluminum-fumarate (Al-Fum), is investigated. As a proof of concept, the pristine Al-Fum MOF is synthesized by the solvothermal reaction process, and the defect engineering method namely solvent-assisted linker exchange, is applied to create the defective Al sites. The defective Al sites play an important role in ensuring the N 2 RR activity for defective Al-Fum. It is found that only the defective Al-Fum enables stable and effective electrochemical N 2 RR, in terms of the highest production rate of 53.9 µg(NH 3 ) h -1 mg cat -1 (in 0.4 m K 2 SO 4 ) and the Faradaic efficiency of 73.8% (in 0.1 m K 2 SO 4 ) at -0.15 V vs reversible hydrogen electrode) under ambient conditions. Density functional theory calculations confirm that the N 2 activation can be achieved on the defective Al sites. Such sites also allow the subsequent protonation process via the alternating associative mechanism. This defect characteristic gives the main group Al-based MOFs the ability to serve as promising electrocatalysts for N 2 RR and other attractive applications.