Selectively Reducing Nitrate into NH3 in Neutral Media by PdCu Single-Atom Alloy Electrocatalysis

Electrocatalytic nitrate reduction reaction (NO3–RR) technology provides a promising solution to recover the nitrate nutrition from wastewater through catalyzing nitrate reduction into value-added NH3. However, the selectivity and efficiency of electrocatalysts are frustrated due to the imbalance of *H adsorption (for NO3 hydrogenation) and unavoidable adjacent *H self-coupling on active sites, resulting in competitive hydrogen evolution reaction (HER). Here, we report a PdCu single-atom alloy (SAA) catalyst that allows isolated Pd sites to produce *H for the hydrogenation process of *NO3 on neighboring Cu sites, which can restrain the *H self-coupling through extending the distance between two *H and thus effectively suppress competitive HER. Consequently, the PdCu SAA catalyst exhibits an ultrahigh NH3 Faraday efficiency (FE) of 97.1% with a yield of 15.4 μmol cm–2 h–1 from the electrocatalytic NO3–RR in the neutral electrolyte, outperforming most of the reported catalysts. Single-crystal experiments and theoretical calculations further prove that the introduction of atomic Pd on the Cu (100) surface could serve as the main active site and greatly decrease the energy barrier of the rate-determining step (RDS) on Cu from ΔG = 0.39 eV (*NOO → *NOOH) to ΔG = 0.10 eV of *NOH → *NHOH on PdCu SAA.