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

The electrochemical nitrate reduction reaction (NO RR) for ammonia (NH) 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 RR and understanding the associated reaction mechanisms for NH synthesis is vital. Herein, a versatile approach is presented to construct platinum based high-entropy intermetallic (HEI) library for NH 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 PtFeCoNiCu 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.