N-Doped Carbon Nanotubes Nucleated through Cobalt Nanoparticles as Bifunctional Catalysts for Zinc–Air Batteries

We introduce an environmentally sustainable approach to create uniformly nitrogen-incapacitated carbon nanotubes nucleated through cobalt nanoparticles. A unique architecture involving carbon shells on Co nanoparticles exists along with the surface morphology prompted by the existence of various nitrogen moieties. The Co nanoparticles are covered by graphitic carbon shells and confined within a defective porous carbon framework, enhancing the surface area and porosity and exposing large active centers for catalytic activities. Our approach uses a single-step in situ synthesis process, which yields these exceptionally good bifunctional electrocatalysts for oxygen evolution reaction, oxygen reduction reaction, and zinc–air battery applications. These massive active centers and pores provide the advantage of exceptional oxygen reduction reaction (ORR) performance. Our samples with Co-embedded carbon nanotubes with optimal N-doping exhibit a higher half-wave potential (E1/2) of ∼0.882 V vs a reversible hydrogen electrode (RHE) compared to a standard Pt/C electrode (∼0.874 V vs RHE) in aqueous 0.1 M KOH solution, at the same catalyst-mass loading. For zinc–air batteries, our samples, as air-reducing catalysts, exhibit a high open-circuit voltage of 1.512 V and an impressive peak power density (150.6 mW cm–2), which surpasses the commercial Pt/C + RuO2 catalysts (92.4 mW cm–2), as well as many reported bifunctional electrocatalysts. Hence, our samples are potential candidates for the coherent depiction of multifunctional, efficient, and durable electrocatalysts for the straightforward, inexpensive, and scalable fabrication of rechargeable zinc–air batteries.