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·mgcat–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·mgcat–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.