Periodic Adjacent Pd‐Fe Pair Sites for Enhanced Nitrate Electroreduction to Ammonia via Accelerating Proton Relay

Abstract Recently, bimetallic nanoparticles (NPs) are promising for driving nitrate (NO 3 − ) reduction reaction (NO 3 RR) to produce ammonia (NH 3 ) due to their multiple active sites and electron redistribution via strong metal–metal interaction. However, the quantitatively determining the atomic configuration of the active sites and revealing their respective roles in NO 3 RR process are still challenged. Herein, the configuration of atomically ordered PdFe 3 L1 2 intermetallic NPs into mesoporous carbon nanofibers (O‐PdFe 3 ‐mCNFs) is reported as an efficient NO 3 RR catalyst for NH 3 synthesis. Compared to the face‐centered cubic one, the O‐PdFe 3 ‐mCNFs demonstrate a high NO 3 − removal of 98.3% within 270 min with a large NH 3 yield rate of 1014.2 µmol h −1 cm −2 . The detailed in situ and theoretical analysis reveals that the high performance of O‐PdFe 3 ‐mCNFs is attributed to the synergetic effect from the periodic adjacent Pd‐Fe pair sites at the ordered (110) facet via accelerating proton relay, where the Fe sites show preferable stabilization of nitrogen−oxygen (*NO) intermediates while Pd sites serve as proton reservoir for *NO hydrogenation. Moreover, the strong d ‐ d orbital hybridization tunes d ‐band center of the alloy NPs and effectively modulates the adsorption energy of *NO 3 − and *NO. This synergetic electrocatalyst design offers a new avenue for developing highly efficient multifunctional NO 3 RR catalysts.