Unveiling the Dual Reduction Pathways in Nitrate Electroreduction to Ammonia on Pd-Doped Perovskite Oxides

Electrocatalytic nitrate reduction reaction (NO 3 RR) offers a sustainable route for ammonia synthesis, yet the contributions of electron-mediated reduction (EMR) and adsorbed hydrogen-mediated reduction (HMR) pathways remain poorly understood. Here, we use LaCoO 3 perovskite as a model system and introduce B-site Pd substitution to modulate these pathways. The optimal LaCo 0.9 Pd 0.1 O 3 achieves an NH 3 yield rate of 0.745 mmol h −1 cm −2 with a Faradaic efficiency of 100% at −0.6 V vs. RHE. Through cyclic voltammetry, electron spin resonance, and quenching experiments with tert-butyl alcohol, we quantitatively distinguish the EMR and HMR contributions, revealing that Pd doping promotes both pathways, with HMR exhibiting a volcano-type potential dependence. In situ FTIR, online DEMS, and DFT calculations show that Pd doping induces oxygen vacancies, enhances nitrate adsorption, lowers the energy barrier for HNO 2 -to-NO reduction, and suppresses H 2 evolution by stabilizing *H intermediates. The promotional effect of Pd is further validated in other perovskites. Our findings provide mechanistic insights into the dual reduction pathways and this will inspire further studies to improve NO 3 RR activity by regulating the reduction pathways.