General synthesis of neighboring dual-atomic sites with a specific pre-designed distance via an interfacial-fixing strategy.

A potential non-precious metal catalyst for oxygen reduction reaction should contain metal-N(4) moieties. However, most of the current strategies to regulate the distances between neighboring metal sites are not pre-designed but depend on the probability by tuning the metal loading or the support. Herein, we report a general method for the synthesis of neighboring metal-N(x) moieties (metal = Fe, Cu, Co, Ni, Zn, and Mn) via an interfacial-fixing strategy. Specifically, polydopamine is used to coat nanotemplates made of metal oxides, followed by pyrolysis to form a metal-oxide skeleton coated by rich nitrogen-doped carbon shells. After chemically etching the skeleton, only interfacial metal atoms strongly bonded with the support via nitrogen atoms are retained. The high purity (>95%) of dual Fe sites was confirmed by both the direct visualization of local regions and the indirect evidence of the averaged information. When these neighboring metal-N(x) moieties are applied for oxygen reduction reaction, Fe-N(x) moieties exhibit the superior activity, even outperforming commercial Pt/C in the aspects of the half-wave potential, methanol tolerance, carbon monoxide tolerance, and robustness.