Surface-Engineered Molybdenum Oxide with Cucurbit[6]uril for Enhanced Nitrogen Reduction Electrocatalysis

Electrocatalytic nitrogen reduction (NRR) offers a sustainable pathway for ammonia (NH₃) production but is challenged by the low solubility of N₂ in aqueous electrolytes, the high energy barrier of N₂ activation, and the competing hydrogen evolution reaction (HER). Herein, cucurbit[6]uril (CB[6]) is immobilized onto the surface of molybdenum oxide (CB[6]@MoO₂). The CB[6]@MoO₂ catalyst exhibits a high NH₃ production rate of 27.7 µg h^-1 mg^-1 and a FE of 25.3% at -0.35 V (vs. RHE) with a 0.1 M Cs₂SO₄ solution as the electrolyte in a flow cell, significantly outperforming bare MoO₂ (7.1 µg h^-1 mg^-1, 3.7%). Mechanistic studies reveal that the immobilized CB[6] on MoO₂ forms a host-guest complex with N₂ with the assistance of alkaline metal cations (e.g., Cs⁺) as dynamic "lids", concentrating and stabilizing N₂ within its hydrophobic cavity and inducing an interfacial electric field that facilitates N≡N bond activation, while the hydrophobic cavity of CB[6] enables excluding overwhelming water to suppress HER. The synergy of CB[6] on the MoO₂ surface through hydrophobic modification, selective N₂ molecular encapsulation, and local polarized electric field enhancement for N₂ activation dramatically improves NRR efficiency, demonstrating a supramolecular surface-engineering strategy to address key limitations in aqueous NRR catalysis.