High-Entropy Alloy-Induced Triple Synergistic Modulation for Enhanced Electrocatalytic Nitrate Reduction to Ammonia.

The electrochemical nitrate reduction reaction (NO3 -RR) provides a promising strategy for sustainable ammonia (NH3) synthesis. However, achieving efficient NO3 -RR remains a great challenge, primarily due to the kinetic mismatch among NO3 --to-NO2 -, NO2 --to-NH3, and H2O dissociation to *H. Here, a multi-site CuCoNiPdAu high-entropy alloy (HEA) catalyst is designed for NO3 -RR, achieving an impressive NH3 high yield rate of 369.1 mg h-1 mgcat -1 with a corresponding NH3 Faraday efficiency of 93.2% at -0.4 V vs. reversible hydrogen electrode, exceeding most of the electrocatalysts reported recently. Moreover, a Zn-NO3 - battery assembled with this HEA as the cathode delivers a remarkable power density of 7.37 mW cm-2 and an NH3 yield rate of 2.0 mg h-1 cm-2, enabling simultaneous electricity generation and NH3 production. Experimental and theoretical results demonstrate that the multi-site feature of the CuCoNiPdAu HEA surface induces triple synergistic modulation toward boosting the NO3 -RR performance: Cu-Ni sites promote the conversion of NO3 - to *NO2, Co-based sites facilitate the transformation of *NO2 to NH3, and Ni sites accelerate the dissociation of H2O to supply abundant *H. This study provides valuable insights for the rational design of HEAs with multiple active sites tailored for multi-step reactions.