Effects of Phase-Transition-Enabled Atomic Shuttling Between Nanoparticles and Single-Atom Sites for Boosted Formic...

Precious metal nanoparticles generally aggregate through Ostwald ripening in the absence of anchoring sites, whereas in the presence of suitable coordination environments, they can disperse into thermodynamically stable single-atom (SA) with chelate structures. Herein, an unexpected staggered transformation between nanoparticles and SAs on nitrogen-doped carbon (CN) is reported. M (M = Rh, Ir, Pt)-Zn intermetallic compound (IMC) nanoparticles together with Ru SAs were initially constructed on CN at 800 °C, and were transformed into M SAs and Ru nanoparticles after annealing at 1000 °C. Metadynamics simulations indicate that Ru─N bond cleavage followed by Rh refilling is kinetically accessible at 1000 °C, with a free-energy barrier of ∼2.30 eV. The resulting Rh₁₂Ru₁ + Rh-N configuration is structurally favored because of its higher d-band filling and stronger covalent Rh-N interactions, under which Rh tends to adopt an electronically rigid coordination environment. Benefiting from the cooperation between Rh SAs and Ru nanoparticles, a mass activity of 62.1 A mg^-1 was achieved for formic acid electrooxidation (FAOR), which is four times higher than that of Rh SAs (15.9 A mg^-1). This work provides new insights into the direction of atomic shuttling between precious metal species.