Accelerating Tandem Electroreduction of Nitrate to Ammonia via Multi‐Site Synergy in Mesoporous Carbon‐Supported High‐Entropy Intermetallics

Abstract The electrochemical nitrate reduction reaction (NO ₃ ⁻ RR) for ammonia (NH ₃ ) synthesis represents a significant technological advancement, yet it involves a cascade of elementary reactions alongside various intermediates. Thus, the development of multi‐site catalysts for enhancing NO ₃ ⁻ RR and understanding the associated reaction mechanisms for NH ₃ synthesis is vital. Herein, a versatile approach is presented to construct platinum based high‐entropy intermetallic (HEI) library for NH ₃ synthesis. The HEI nanoparticles (NPs) are uniformly supported on a 2D nitrogen doped mesoporous carbon (N‐mC) framework, featured with adjustable compositions (up to eight elements) and a high degree of atomic order (over 90%). Guided by the density functional theory (DFT) calculations and atomic structural analysis, a quinary Pt _0.8 Fe _0.2 Co _0.2 Ni _0.2 Cu _0.2 HEI NPs based N‐mC catalyst is designed, which demonstrates a large ammonia Faradaic efffciency (>97%) and a remarkable recyclability (>20 cycles) under both acidic and basic conditions. The combined in situ experimental analysis and further DFT calculation suggests that the well‐defined multi‐sites nature of the HEI NPs cooperate for a tandem reduction mechanism, in which the Pt‐X (X represents the other four transition elements) bridging sites offer optimal adsorption for key nitrogen–oxygen species while the Pt sites facilitate the generation and adsorption of *H species.