M-N_x/C (M = Fe, Co) type electro-catalyst as a promising alternative to Pt-based electro-catalyst for oxygen reduction reaction (ORR) in fuel cells has been studied for years. However, the mechanism of this four-electron process involving several successive steps and the dynamic intermediate (hydrogen peroxide) participation still remains obscure. In this study, a series of Co-N_x/C with varied densities of Co-N_x sites have been obtained for probing the ORR activity and pathway in acid media via adopting zinc ions as a size-comparable template to disperse and regulate Co-N_x sites. Importantly, it has been found that the half-wave potential can be positively correlated with the weight percentage of ionic cobalt species, which suggests the decisive role of the density of Co-N_x sites on ORR activity. More importantly, our results suggest that both Co-N_x/C and 20 wt% Pt/C catalyze ORR via two successive steps: ORR begins at the onset potential accompanying the generation of H₂O₂ intermediate, which is more easily to be adsorbed on platinum than on Co-N_x/C surface as detected by ring electrode; Subsequently at the half-wave potential and more negative, H₂O₂ is further reduced immediately and efficiently on platinum, but unfortunately at much lower rate on Co-N_x/C. Thus in addition to improving the initial ORR activity by maximizing the M-N_x coordination, it will be of great significance to endow the non-platinum catalysts with surface active sites capable of adsorbing and efficiently reducing the H₂O₂ intermediate for the complete oxygen reduction to water.

MN _x / C（M = Fe，Co）型电催化剂作为燃料电池中氧还原反应（ORR）的Pt基电催化剂的有前途的替代品，已经进行了多年研究。但是，这种涉及多个连续步骤的四电子过程的机理以及动态中间产物（过氧化氢）的参与仍然不清楚。在这项研究中，通过采用锌离子作为可比尺寸的模板分散和调节Co ，获得了一系列具有不同密度Co-N _x位点的Co-N _x / C，用于探测酸介质中的ORR活性和途径。-N _x网站。重要的是，已发现半波电势与离子钴物种的重量百分比呈正相关，这表明Co-N _x位点密度对ORR活性具有决定性作用。更重要的是，我们的结果表明Co-N _x / C和20 wt％Pt / C都通过两个连续步骤来催化ORR ：ORR从伴随H ₂ O ₂中间体生成的起始电位开始。环形电极检测到，与Co-N _x / C表面相比，吸附在铂上的吸附量更高；随后在半波电势和更多负值处，H ₂ O ₂在铂上可以立即有效地进一步降低汞的含量，但不幸的是在Co-N _x / C上速率要低得多。因此，除了通过最大程度地提高MN _x配位来提高初始ORR活性外，赋予非铂催化剂表面活性位能够吸附并有效还原H ₂ O ₂中间体以完全还原氧也具有重要意义。浇水。