Moreover, the stability issues of Pt-based catalysts (e.g., the crystallite dissolution and nanoparticle agglomeration) have also jeopardized the reliability of power systems including ORR as a half reaction. [7,8] In these regards, there is a general call for the replacement of the Pt-based composites with cost-effective, durable and highly active ORR catalysts.During the past few years, nitrogencoordinated transition metal species (TM-N x ) that are embedded within a carbon matrix have emerged as a class of promising catalysts for ORR, owing to their high activity, maximum utilization of the metal species and distinct configurations of active sites. Among them, the Fe-N-C catalysts demonstrate an exceptional ORR catalytic activity that is even comparable to the Pt/C benchmark. [9,10] Nevertheless, the usual insufficient durability of the Fe-N x species under long-term ORR operation has severely impeded their potential for commercial perspectives. [11] Although the actual degradation mechanism of Fe-N x centers is still under debate, it is clear that the reactive oxygen species (ROS) generated during the "electro-Fenton" process in the presence of Fe species and hydrogen peroxide tend to cause corrosion or oxidation of carbon that leads to the cleavage of Fe-N bond and the eventual decay of activity. [12,13] By contrast, CoN x -containing materials would have less deleterious effects in this regard and appear to be promising alternatives to the Fe-N-C catalysts in various applications, [14] as reported recently. [15,16] Nonetheless, despite significant progress in preparation methods, [17,18] it is still extremely challenging for CoN x -containing catalysts to be applied in large scale due to i) their insufficient activity compared with the Pt-based catalysts; [14,19] and ii) the relatively high percentage of H 2 O 2 produced during ORR that results in a lower energy efficiency and possible catalyst corrosion. [4,20,21,22] Thus, it is necessary to develop a strategy to enhance the catalytic ORR performance of the Co-N-based composites meanwhile suppress the H 2 O 2 production on them. [23] Herein, Cu species are introduced to mitigate the activity and high H 2 O 2 selectivity issues of Co-N based composites. For the first time, the different roles of CuN x and CoN x moieties in ORR have been investigated within a multicomponent Co/ Cu catalyst, both experimentally and theoretically. Atomically dispersed CuN x sites are proposed to be effective in reducing Rational design of cost-effective and active electrocatalysts is an essential step toward the large-scale realization of hydrogen fuel cells and metal-air batteries. Its success requires a drastic improvement in the kinetics of the cathodic oxygen reduction reaction (ORR). Herein, a novel ORR catalyst formed by encapsulating thin Cu layer decorated Co nanoparticles inside graphitic carbon layers that are embedded with abundant CoN x and CuN x atomic sites (denoted as SA-CoCu@Cu/CoNP), is reported. The multicomponent SA-CoCu@Cu/CoNP composite exhibits a r...