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 torecoverthe nitrate nutrition from wastewater through catalyzing nitrate reductioninto value-added NH3. However, the selectivity and efficiencyof electrocatalysts are frustrated due to the imbalance of *H adsorption(for NO3 hydrogenation) and unavoidable adjacent *H self-couplingon active sites, resulting in competitive hydrogen evolution reaction(HER). Here, we report a PdCu single-atom alloy (SAA) catalyst thatallows isolated Pd sites to produce *H for the hydrogenation processof *NO3 on neighboring Cu sites, which can restrain the*H self-coupling through extending the distance between two *H andthus effectively suppress competitive HER. Consequently, the PdCuSAA catalyst exhibits an ultrahigh NH3 Faraday efficiency(FE) of 97.1% with a yield of 15.4 & mu;mol cm(-2) h(-1) from the electrocatalytic NO3 -RR in the neutral electrolyte, outperforming most ofthe reported catalysts. Single-crystal experiments and theoreticalcalculations further prove that the introduction of atomic Pd on theCu (100) surface could serve as the main active site and greatly decreasethe energy barrier of the rate-determining step (RDS) on Cu from & UDelta;G = 0.39 eV (*NOO & RARR; *NOOH) to & UDelta;G = 0.10 eV of *NOH & RARR; *NHOH on PdCu SAA.