Co single atoms and Co nanoparticle relay electrocatalyst for rechargeable zinc air batteries

The commercialization of rechargeable zinc air batteries (ZABs) requires the discovery of high-performance, low-cost and durable bifunctional oxygen electrocatalysts. In this work, we report nitrogen doped carbon nano/microtubes confined metallic cobalt nanoparticles and single atoms (Co@NCNT/Co-SA@NCMT) as robust oxygen electrocatalyst for rechargeable ZABs. Co@NCNT/Co-SA@NCMT exhibits 18 times better ORR performance than Co@NCNT ascribed to the relay catalysis by Co-SAs and Co-NPs via O2→H2O2→H2O pathway. Experimental and theoretical investigations reveal that Co-SAs are capable of efficient oxygen reduction to H2O2, which is further reduced to H2O by Co-NPs due to its higher oxophilicity. Besides, due to the formed microtubes, the overpotential at 100 mA cm−2 in OER catalysis is lowered by 130 mV for Co@NCNT/Co-SA@NCMT than Co@NCNT. The power density of the assembled rechargeable ZAB is 155 mW cm−2 for Co@NCNT/Co-SA@NCMT outperforming the noble-metal counterpart (Pt/CB-IrO2: 71 mW cm−2). Furthermore, a superior stability with inappreciable increment in voltage gap for 300 h is achieved. Co@NCNT/Co-SA@NCMT also performs its high potential in the practical application with a maximum battery performance of 120 mW cm−2 sustained for 17 h in all-solid-state ZABs test. [Display omitted] •Co nanoparticles and single atoms confined by nitrogen doped nano/microtubes are formed.•Co@NCNT/Co-SA@NCMT requires lower overpotential at 100 mA cm−2 in OER than Co@NCNT.•ORR activity of Co@NCNT/Co-SA@NCMT is 18 times better than Co@NCNT.•Co@NCNT/Co-SA@NCMT exhibits 2.2-fold higher power density than Co@NCNT.