Boosting Electrocatalytic Ammonia Synthesis via Main-Group Metal Doping and Ionic Liquid Encapsulation in Copper Metal-Organic Frameworks.

Abstract

The electrochemical nitrogen reduction reaction (EN₂RR) provides a sustainable method for synthesizing ammonia at room temperature, but it is hindered by the low ammonia faradic efficiency (FE) and production yield. Herein, we report an effective EN₂RR electrocatalyst: the ionic liquid-encapsulated aluminum copper bimetallic metal-organic framework (IL-AlCu-MOF). Comparisons across pristine Cu-MOF, AlCu-MOF, IL-Cu-MOF, and IL-AlCu-MOF reveal that the combination of Al doping and IL encapsulation can simultaneously promote dinitrogen activation and accelerate proton generation via water dissociation in a neutral electrolyte, which synergistically enhances the yield and selectivity of ammonia in EN₂RR. The IL-AlCu-MOF achieves an NH₃ yield of 124.7 μg·h^-1·mg_cat^-1 with an FE_NH₃ of 20.3% at -0.3 V (vs reversible hydrogen electrode, RHE) in 0.1 M K₂SO₄. In situ attenuated total reflectance surface-enhanced infrared absorption spectroscopy (ATR-SEIRAS) measurements indicate improved water dissociation kinetics over that of IL-AlCu-MOF, and differential electrochemical mass spectrometry (DEMS) captures the EN₂RR intermediates. Density functional theory (DFT) calculations show that Al doping modulates the Cu electronic structure for enhanced N₂ activation, while IL encapsulation strengthens water adsorption at the MOF surface and thus accelerates water dissociation, both of which contribute to boosting the EN₂RR performance.