Electrochemical NO 3 - Reduction Catalyzed by Atomically Precise Ag 30 Pd 4 Bimetallic Nanocluster: Synergistic Catalysis or Tandem Catalysis?

Electrochemically converting NO ₃ ^- compounds into ammonia represents a sustainable route to remove industrial pollutants in wastewater and produce valuable chemicals. Bimetallic nanomaterials usually exhibit better catalytic performance than the monometallic counterparts, yet unveiling the reaction mechanism is extremely challenging. Herein, we report an atomically precise [Ag ₃₀ Pd ₄ (C ₆ H ₉ ) ₂₆ ](BPh ₄ ) ₂ (Ag ₃₀ Pd ₄ ) nanocluster as a model catalyst toward the electrochemical NO ₃ ^- reduction reaction (eNO ₃ ^- RR) to elucidate the different role of the Ag and Pd site and unveil the comprehensive catalytic mechanism. Ag ₃₀ Pd ₄ is the homoleptic alkynyl-protected superatom with 2 free electrons, and it has a Ag ₃₀ Pd ₄ metal core where 4 Pd atoms are located at the subcenter of the metal core. Furthermore, Ag ₃₀ Pd ₄ exhibits excellent performance toward eNO ₃ ^- RR and robust stability for prolonged operation, and it can achieve the highest Faradaic efficiency of NH ₃ over 90%. In situ Fourier-transform infrared study revealed that a Ag site plays a more critical role in converting NO ₃ ^- into NO ₂ ^- , while the Pd site makes a major contribution to catalyze NO ₂ ^- into NH ₃ . The bimetallic nanocluster adopts a tandem catalytic mechanism rather than a synergistic catalytic effect in eNO ₃ ^- RR. Such finding was further confirmed by density functional theory calculations, as they disclosed that Ag is the most preferable binding site for NO ₃ ^- , which then binds a water molecule to release NO ₂ ^- . Subsequently, NO ₂ ^- can transfer to the vicinal exposed Pd site to promote NH ₃ formation.