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The arrangement of the active sites on the surface of a catalysts can reduce the problem of mass transfer and enhance the atom economy. Herein, supported Ni metal nanoparticles can be transformed to thermal stable Ni single atoms, mostly located on the surface of the support. Assisted by N-doped carbon with abundant defects, this synthetic process not only transform the nanoparticles to single atoms, but also creates numerous pores to facilitate the contact of dissolved CO and single Ni sites. The proposed mechanism is that the Ni nanoparticles could break surface C-C bonds drill into the carbon matrix, leaving pores on the surface. When Ni nanoparticles are exposed to N-doped carbon, the strong coordination splits Ni atoms from Ni NPs. The Ni atoms are stabilized within the surface of carbon substrate. The continuous loss of atomic Ni species from the NPs would finally result in atomization of Ni NPs. CO electroreduction testing shows that the surface enriched with Ni single atoms delivers better performance than supported Ni NPs and other similar catalysts.

It is highly desired but remains a great challenge to develop nonprecious metal single-atom catalysts to supersede the Pt-based material for oxygen reduction reaction (ORR). Herein, we report a porous nitrogen-doped carbon matrix catalyst with 3.5 wt % single Fe atoms (Fe SAs/N–C) through a versatile molecules-confined pyrolysis strategy. In 0.1 M KOH condition, the Fe SAs/N–C catalyst possesses a half-wave potential of 0.91 V vs RHE. In a more challenging acidic solution, Fe SAs/N–C catalyst also offers good ORR activity, comparable with the commercial Pt/C. Impressively, Fe SAs/N–C shows extremely high stability both in alkaline and acidic media. In addition, this Fe SAs/N–C-derived Zn–air battery and proton exchange membrane fuel cells (PEMFCs) exhibit high performance. This work opens an avenue for designing and preparing single-atom catalysts.

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