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

Abstract Electrocatalytic nitrogen reduction (NRR) offers a sustainable pathway for ammonia (NH ₃ ) production but is challenged by the low solubility of N ₂ in aqueous electrolytes, the high energy barrier of N ₂ activation, and the competing hydrogen evolution reaction (HER). Herein, cucurbit[6]uril (CB[6]) is immobilized onto the surface of molybdenum oxide (CB[6]@MoO ₂ ). The CB[6]@MoO ₂ catalyst exhibits a high NH ₃ 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 Cs ₂ SO ₄ solution as the electrolyte in a flow cell, significantly outperforming bare MoO ₂ (7.1 µg h ⁻¹ mg ⁻¹ , 3.7%). Mechanistic studies reveal that the immobilized CB[6] on MoO ₂ forms a host–guest complex with N ₂ with the assistance of alkaline metal cations (e.g., Cs ⁺ ) as dynamic “lids”, concentrating and stabilizing N ₂ 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 MoO ₂ surface through hydrophobic modification, selective N ₂ molecular encapsulation, and local polarized electric field enhancement for N ₂ activation dramatically improves NRR efficiency, demonstrating a supramolecular surface‐engineering strategy to address key limitations in aqueous NRR catalysis.