General synthesis of carbon-guarded cobalt-based nanospheres for oxygen reduction electrocatalysis

Abstract

Constructing efficient nanocatalysts for the oxygen reduction reaction (ORR) is crucial for the widespread application of metal–air batteries. Herein, we construct carbon-guarded cobalt-based nanospheres composed of metal nanoparticles encased in a nitrogen doped carbon shell (M@NC NPs, where M stands for metal or alloy) through a bifunctional gas phase heat treatment technique. Compared to monometallic and polymetallic nanospheres, bimetallic nanospheres of Ni/Co@NC NPs exhibit enhanced ORR activity, even comparable to that of the commercial Pt/C catalyst, and have robust catalytic stability. In situ Raman spectra analysis during the ORR electrocatalysis reveals a strong interaction between the carbon shell of Ni/Co@NC NPs and the ORR intermediates. Moreover, Ni/Co@NC NPs show superior catalytic capability compared to Pt/C in a battery system, resulting in improved discharging performance in a home-made zinc–air battery, this includes higher peak power density (185.5 mW cm⁻²), better rate performance, and larger discharging capacity (817 mA h g_Zn⁻¹). These impressive catalytic performances are attributed to the three-dimensional structure that contains carbon-guarded Ni/Co alloy nanoparticles, the partially graphitized nitrogen-doped carbon shell that is dispersed with Ni/Co active moieties, and the electronic effect of the Ni/Co alloy on the carbon shell. This work provides a general strategy for synthesizing durable carbon-guarded and metal-diversified nanosphere electrocatalysts for efficient energy conversion.