Dual-metal single-atom CoNi–NCs encapsulated CoNi bimetallic nanoparticles as durable oxygen-reduction catalysts for zinc-air batteries

Dual-metal single-atom catalysts (DACs) can break the electronic and structural symmetries of the M–N₄ unit and have attracted intensive attention. In this work, CoNi@CoNi–NCs were prepared via an impregnation-reduction method, which possess coexisting CoNi–NC DACs and encapsulated CoNi dilute alloy nanoparticles (NPs). After optimizing the Co/Ni atomic ratio, Co 10 Ni 1 @CoNi–NC exhibited superior oxygen reduction reaction (ORR) durability. After 30,000 accelerated durability test (ADT) cycles, the half-wave potential of CoNi@CoNi–NCs only decreased by 15 mV, which is significantly better than commercial Pt/C (72 mV). Zinc–air battery (ZAB) tests demonstrated that the Co 10 Ni 1 @CoNi–NC ZAB achieved the peak power density of 149.91 mW cm −2 , which is much higher than that of commercial Pt/C (122.65 mW cm −2 ). After 240 h of charge-discharge cycling, the Co 10 Ni 1 @CoNi–NC ZAB maintained stable voltage efficiency with only a 14.9% decay, which is much better than that of commercial Pt/C. Based on the advanced and comprehensive experimental and theoretical analyses, the enhanced ORR performance of Co 10 Ni 1 @CoNi–NC in alkaline conditions can be attributed to the following reasons. (1) The influence of trace amounts of nickel on the Co 2+ and Co N electronic structures. (2) The regular morphological structure increases the number of pores and enhances the utilization rate of active sites. (3) The unique carbon coated structure. (4) The synergistic effect between CoNi NPs and CoNi–NCs. This work helps to understand the interplay between NPs and DACs and provides guidance for the further development of non-noble metal ORR catalysts.