The occurrence of high concentrations of nitrate in various water resources is a significant environmental and human health threat, demanding effective removal technologies. Single atom alloys (SAAs) have emerged as a promising bimetallic material architecture in various thermocatalytic and electrocatalytic schemes including nitrate reduction reaction (NRR). This study suggests that there exists a stark contrast between thermocatalytic (T-NRR) and electrocatalytic (E-NRR) pathways that resulted in dramatic differences in SAA performances. Among Pd/Cu nanoalloys with varying Pd-Cu ratios from 1:100 to 100:1, Pd/Cu_(1:100) SAA exhibited the greatest activity (TOF_Pd = 2 min^-1) and highest N₂ selectivity (94%) for E-NRR, while the same SAA performed poorly for T-NRR as compared to other nanoalloy counterparts. DFT calculations demonstrate that the improved performance and N₂ selectivity of Pd/Cu_(1:100) in E-NRR compared to T-NRR originate from the higher stability of NO₃* in electrocatalysis and a lower N₂ formation barrier than NH due to localized pH effects and the ability to extract protons from water. This study establishes the performance and mechanistic differences of SAA and nanoalloys for T-NRR versus E-NRR.

Electrosynthesis of ammonia using nitrogen and water provides a potential alternative to the thermochemical process (Haber-Bosch) in a clean, sustainable, and decentralized way when electricity is generated from renewable sources. To enable the widespread commercialization of this technology, an electrocatalyst to convert nitrogen (N₂) to ammonia (NH₃) with high selectivity and activity must be developed. Here, we report our findings in the investigation into the role of incorporating palladium (Pd) in bimetallic Au-Ag nanocages on the electrocatalytic activity of the nitrogen reduction reaction (NRR) under ambient conditions. The localized surface plasmon resonance (LSPR) peak position of the resulting trimetallic nanoparticles is tuned with Pd concentration, achieving the highest electrocatalytic NRR activity (NH₃ yield rate = 5.80 μg cm⁻² h⁻¹, Faradaic efficiency = 48.94%) using Au-Ag-Pd-850 nanoparticles at −0.3 V vs RHE. This activity corresponds to the production energy efficiency of 28.9% with an electrical energy input of 19.1 MWh / ton _NH3. The enhanced NRR activity is attributed mainly to the formation of a highly porous Pd layer with remarkably high surface area active for NRR. In addition, operando surface-enhanced Raman spectroscopy (SERS) is used to probe the mechanism of NRR on the trimetallic nanostructures and to identify the intermediate species at the electrode-electrolyte interface.