Synergistic effects between single-atom Co–N–C and embedded CoNi dilute-alloy nanoparticle boost the acidic oxygen reduction reaction

Single-atom catalysts (SACs) have received extensive attention due to their theoretically 100 % atomic utilization, low cost and unique catalytic performance. In this work, CoNi@CoNCs were prepared via impregnation-reduction method. CoNi@CoNCs possess coexisting Co–N–C SAC and CoNC-coated CoNi dilute alloy nanoparticles (NPs), in which Co NPs are doped with trace Ni amount. After optimizing the Co/Ni atomic ratio and heat treatment temperature, the CoNi@CoNCs exhibit exceptional acidic oxygen reduction reaction (ORR) activity with a half-wave potential of 0.754 V and a double-layer capacitance of 48.42 mF cm −2 in 0.1 M HClO 4 solutions. After 10,000 cycles of degradation test, the half-wave potential of the Co 8 Ni 1 @CoNC-600(Co 8 Ni 1 Co/Ni atomic ratio 8:1 in the precursor; 600 = heat treatment temperature 600 °C) only decreased by 35 mV. According to advanced and comprehensive experimental and theoretical analyses, the reasons for the improvement toward acidic ORR activity and stability of the CoNi@CoNC can be attributed to the following several reasons.(1) the Co 2+ and Co–N electron structures influenced by the trace Ni amount.(2) The unique CoNC-coated structure. (3) The synergistic effect between CoNi NPs and Co single atoms. This work helps to expound the specific role of NPs in SACs, providing theoretical guidance for the further development of non-noble metal NPs and single-atom co-component catalysts.