Insight into role of Ni/Fe existing forms in reversible oxygen catalysis based on Ni‐Fe single‐atom/nanoparticles and N‐doped carbon

Oxygen catalysis reactions play essential roles in metal‐air batteries, fuel cells, water electrolysis and artificial photosynthesis, with their development receiving significant attention in recent years. Understanding the structure–activity relationship plays an important role in the construction and performance optimization of reversible oxygen catalyst. In this work, a facile method is applied to synthesize Ni‐Fe dual‐metal single‐atom/nanoparticle combined with N‐doped carbon (Ni‐Fe SA/N‐C and Ni‐Fe NP/N‐C). For oxygen reduction reaction (ORR), Ni‐Fe SA/N‐C shows excellent activity, and the initial potential and half‐wave potential are 0.96 and 0.90 V, respectively, which are higher than those of commercial Pt/C; for oxygen evolution reaction (OER), a low overpotential of 330 mV at 10 mA·cm −2 is obtained for Ni‐Fe NP/N‐C, prominently better than that of commercial RuO 2 /C. Through the in‐depth study of the existing forms of Ni/Fe, the difference between ORR and OER activities of Ni‐Fe SA/N‐C and Ni‐Fe NP/N‐C is clarified, and the structure–activity relationship is revealed.