Rigid two-dimensional indium metal–organic frameworks boosting nitrogen electroreduction at all pH values

Abstract

Based on an ion exchange and dissolution–recrystallization mechanism, rigid indium metal–organic framework (In-MOF) nanosheets have been synthesized under mild conditions. The collective advantages of the rigid structure and two-dimensional architecture (thickness: 1.3 nm) enable In-MOF to show great activity during nitrogen electroreduction and excellent stability over a wide pH range. At pH values <7, In-MOF nanosheets demonstrate an ammonia yield rate ≥ 24.70 μg h⁻¹ mg⁻¹ (or 4.94 μg h⁻¹ cm⁻²) and faradic efficiency ≥6.72%. At pH values ≥7, 2D In-MOF can operate efficiently with a record NH₃ yield of 79.20 μg h⁻¹ mg⁻¹ (or 15.94 μg h⁻¹ cm⁻²) and faradic efficiency of 14.98%, making it one of the most active MOF-based electrocatalysts for nitrogen electroreduction. Furthermore, the reaction mechanism of nitrogen electroreduction has been revealed using density function theory (DFT) simulations, and it follows enzymatic pathways at all pH values, with the potential determining step being *H₂NNH₂* → *NH₂ + NH₃. It is expected that the present study will offer valuable clues for the design and fabrication of low-cost and efficient all-pH nitrogen reduction electrocatalysts for industrial applications.