Molten Salt-Assisted Synthesis of Porous Precious Metal-Based Single-Atom Catalysts for Oxygen Reduction Reaction

Precious metal-based single-atom catalysts (PM-SACs) hosted in N-doped carbon supports have shown new opportunities to revolutionize cathodic oxygen reduction reaction (ORR). However, stabilizing the high density of PM-N_x sites remains a challenge, primarily due to the inherently high free energy of isolated metal atoms, predisposing them to facile atomic agglomeration. Herein, a molten salt-assisted synthesis strategy is proposed to prepare porous PM₁/N-C_Pores (PM = Ru, Pt, and Pd) electrocatalysts with densely accessible PM-N_x sites. A hierarchically porous N-doped carbon substrate (N-C_Pores), synthesized via the NaCl-assisted pyrolysis of zeolitic imidazolate framework-8, effectively improves the utilization of PM-N_x sites by increased reactants accessible surface area and reduced mass transfer resistance. In accordance with theoretical calculations, the as-prepared Ru₁/N-C_Pores, featuring superior intrinsic active Ru-N₄ sites, exhibit outstanding ORR turnover frequency of 6.19 e^- site^-1 s^-1, and outperforms the commercial Pt/C with a 5.3-fold of mass activity (5.83 ± 0.61 A mg^-1) at 0.8 V versus reversible hydrogen electrode. The commendable activity and stability of Ru₁/N-C_Pores in a real fuel cell device further affirm its practical applicability.