π–π Stacked Stable Supramolecular Nanocage π-Skeleton and Its Derivatives for Ammonia Synthesis at Normal Temperature and Pressure

The electrochemical reduction of nitrogen to ammonia is a promising approach for large-scale industrial ammonia production due to its low energy consumption and environmental benignity. In this study, a porous π–π stabilized supramolecular nanocage-based π-skeleton (π-2) with a topological structure was hydrothermally prepared. Then, π-2 was used as a support for the in situ growth of Ni₂O₃ to obtain a composite Ni₂O₃/π-2 catalyst. The π–π stacking interaction of π-2 was effectively harnessed to enhance the electrical conductivity of Ni₂O₃, leading to significantly improved electrocatalytic activity for nitrogen reduction to ammonia. When applied for ammonia synthesis under ambient temperature and pressure, π-2 exhibited an NH₃ generation rate of 2.86 μg·h^–1·mg_cat^–1 and FE of 9.6% at a potential of −0.23 V (vs RHE). Meanwhile, the Ni₂O₃/π-2 catalyst exhibited an NH₃ generation rate of 8.22 μg·h^–1·mg_cat^–1 and FE of 5.14% at −0.88 V (vs RHE). These results confirm the electrocatalytic activity of π-2 for nitrogen reduction to ammonia and demonstrate its good potential as an excellent support for transition metal catalysts. The in situ growth of Ni₂O₃ on π-2 reduces the degree of π–π bonding, forms nickel–nitrogen bonds favorable for electron transport, and modulates the electronic structure of the active centers.