Fe/N/C material is the most competitive alternative to precious-metal catalysts for oxygen reduction. In view of the present consensus on active centers, further effort is directed at maximizing the density of single Fe atoms. Here, the imperfections in commonly used doping strategy of Fe for the synthesis of zeolitic imidazolateframework (ZIF)-derived Fe/N/C catalysts are revealed. More importantly, a strikingly improved catalyst is obtained by a ‘second pyrolysis’ method and delivers a half-wave potential of 0.825 V (vs. RHE) in acidic media. The strong confinement effect of carbonaceous host accounts for the formation of dense single-atom sites and thus the high activity. Our findings will potentially facilitate future improvement of M/N/C catalysts.

Fe / N / C材料是用于减少氧气的贵金属催化剂的最具竞争力的替代品。鉴于目前对活性中心的共识，需要进一步努力以使单个Fe原子的密度最大化。在此，揭示了用于合成源自沸石咪唑酸盐骨架（ZIF）的Fe / N / C催化剂的常用Fe掺杂策略的缺陷。更重要的是，通过“第二次热解”方法获得了显着改进的催化剂，并在酸性介质中提供了0.825 V（相对于RHE）的半波电势。碳质宿主的强约束作用解释了密集的单原子位点的形成，因此具有很高的活性。我们的发现将有可能促进M / N / C催化剂的未来改进。