Engineering Ce Promoter to Regulate H ^* Species to Boost Tandem Electrocatalytic Nitrate Reduction for Ammonia Synthesis

Abstract The renewable‐energy‐powered electroreduction of nitrate (NO ₃ RR) to ammonia emerges as a generalist for contamination remediation, green ammonia synthesis, and even advanced energy conversion, garnering significant interest. However, it comes across limited ammonia yield and selectivity due to the imbalance active hydrogen (H ^* ) supply within cutting‐edge single‐center Cu‐based materials. Herein, secondary Ce entity is engineered into Cu/MoO ₂ @C substrate by thermal treatment of Ce‐doping NENU‐5 precursors to provide H ^* effectively. A high NH ₃ yield rate (20.3 ± 0.7 mg h ⁻¹ mg _cat. ⁻¹ ) and NO ₃ ⁻ −to−NH ₃ Faradaic efficiency (92 ± 3%) at −0.4 V (vs RHE) can be reached in 5%Ce‐Cu/MoO ₂ @C, ranking among the recently reported state‐of‐the‐art catalysts. The core of this boosting performance lies in dual‐site tandem catalysis, in which Cu site adsorbs and activates NO ₃ ⁻ , and Ce site dissociates water to generate H ^* , respectively. And the hydrogen spillover from Ce site to vicinal ^* NO _x intermediates on Cu promotes the hydrogenation and ammonia generation with high selectivity. Theoretical calculations further indicate that Ce engineering optimizes the electronic properties, promotes the activation of adsorbed NO ₃ ⁻ , and decreases the energy barrier in the rate‐determining step within dual‐site catalysis. These findings consolidate the positive role of rare earth center and highlight its corresponding dual‐site catalysis in sustainable ammonia synthesis.