Synergistic Dual-Atom Cu Nanozyme for Efficient Electrocatalytic Nitrate Reduction to Ammonia

The electrocatalytic nitrate reduction reaction (NO₃RR) to ammonia (NH₃) represents a promising strategy for sustainable NH₃ synthesis while mitigating nitrate contamination. However, challenges remain for sluggish kinetics and poor selectivity due to inefficient nitrite (NO₂⁻) activation and inadequate generation/utilization of reactive hydrogen species (H*). To address these issues, we design a dual-atom copper nanozyme anchored on hollow carbon spheres (Cu₂-S₁N₄/HCS) by mimicking the enzymatic architecture of copper-containing nitrite reductases (Cu-NIRs). Experimental and theoretical investigations reveal that the Cu-S₁N₂ site facilitates water dissociation to generate H*, which subsequently spills over to the Cu-N₃ site. Meanwhile, the electrons are transferred from Cu-S₁N₂ to Cu-N₃ site induced by regulation of coordination environments, resulting in stabilization of the key NO₃RR intermediates by low-valent Cu at the Cu-N₃ site. In this process, the Cu-N₃ site serves as the catalytic center for inter-site coupling of H*/e⁻ transfer-mediated deoxygenation and hydrogenation of NO₃⁻ to NH₃. The resulting Cu₂-S₁N₄/HCS dual-atom nanozyme delivers a remarkable NO₃⁻-to-NH₃ Faradaic efficiency (FE, 93.1%) and a high NH₃ yield rate (11.8 mg h⁻¹ cm⁻²) at −0.6 V vs. reversible hydrogen electrode (RHE). This work demonstrates a bioinspired strategy that mimics natural Cu-NIRs, which offers an efficient and sustainable route for ammonia production from wastewater.