Highly Selective Electrochemical Nitrate Conversion to Ammonia on Ru-doped Cu Single-Atom Alloy Catalyst

Abstract

The electrochemical nitrate reduction reaction (NO3RR) provides a promising route for wastewater denitrification and NH3 production. Realizing this technology requires electrocatalysts that are highly active and selective for NO3RR to NH3 at low overpotentials. Cu exhibits high activity for NO3RR but suffers from limited NH3 selectivity due to the formation of side products such as NO2–. Here, by engineering the Cu surface to introduce heterogeneous electron-rich/poor catalytic sites, we establish a mechanistic understanding of NO3RR and demonstrate a rigorous design of a Ru-doped Cu single-atom alloy (Ru–Cu-SAA) as an efficient catalyst for selective NO3–-to-NH3 conversion. Density functional theory (DFT) calculations identify the energetically most favorable pathways for NO3RR and reveal more favorable thermodynamics for key NO3RR steps on Ru–Cu-SAA compared to Cu. The calculations further predict higher activity and selectivity for NO3–-to-NH3 conversion on Ru–Cu-SAA than on Cu. Guided by these insights, our experimental studies demonstrated substantially higher activity and NH3 selectivity for NO3RR on a Ru–Cu-SAA catalyst than on a counterpart Cu nanocatalyst, thereby validating the theoretical predictions and proposed reaction mechanisms. Overall, this work establishes a theory–experiment framework for the rational design of Cu-based SAA catalysts with high activity and selectivity for nitrate-to-ammonia conversion.