Cu‐Doped CeO ₂ Solid Solution Enables Efficient and Selective Nitrate‐to‐Ammonia Reduction via f–p–d Orbital Coupling

ABSTRACT Electrochemical nitrate reduction reaction (NO 3 RR) offers a sustainable alternative to the energy‐intensive Haber–Bosch process for ammonia synthesis, yet its efficiency is limited by sluggish hydrogenation kinetics and competing hydrogen evolution. Herein, we report a rare‐earth/transition‐metal regulation strategy by constructing a Cu‐doped CeO 2 solid solution featuring a Ce─O─Cu electronic bridge with gradient 4f–2p–3d orbital coupling. Structural and spectroscopic analyses confirm the incorporation of Cu into the CeO 2 lattice, forming a stable solid solution with strong electronic interaction. X‐ray absorption spectroscopy reveals pronounced charge redistribution within the Ce─O─Cu bridge, inducing a downward shift of the Cu d‐band center and optimizing intermediate hydrogenation. Benefiting from this electronic configuration, the Cu 0.30 Ce 0.70 O 2 /C catalyst achieves an ammonia yield rate of 925.96 µmol cm −2 h −1 at −1.1 V (vs. RHE) and an ammonia Faradaic efficiency of 96.04% at −0.7 V (vs. RHE). Operando Raman and ATR‐FTIR spectroscopy, H/D isotope experiments, and density functional theory calculations reveal that the Ce─O─Cu bridge promotes water dissociation, facilitates proton‐coupled hydrogenation, and lowers the energy barrier of the rate‐determining step ( * NO→ * NOH). This work establishes gradient orbital coupling as an effective strategy for rare‐earth catalyst design and provides insight into efficient and selective nitrate‐to‐ammonia electrocatalysis.