Glucose‐hexamethylenetetramine‐derived Co, N co‐doped carbon nanoflowers with encapsulated Co@Co3O4 as efficient bifunctional oxygen electrocatalyst for zinc‐air batteries

Developing low-cost, eco-friendly, and efficient bifunctional electrocatalysts for both oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) is an important issue for zinc-air batteries. In this study, HMT-Co/G-700 catalyst with nanoflower structure and Co, N co-doped carbon encapsulated Co@Co3O4 nanoparticles are synthesized from D-glucose, hexamethylenetetramine (HMT), and Co(NO3)2. HMT is presented as the complex to uniformly disperse Co@Co3O4 nanoparticles, dope nitrogen, and create the nanoflower structure. The nanoflower structure enhances high surface area to expose the active sites. The formation of Co3O4 via mild oxidation of Co surface provides oxygen vacancies to adsorb O2. HMT-Co/G-700 catalyst exhibits excellent ORR electrocatalytic property, i.e. high onset potential (1.03 V), high half-wave potential (0.83 V), low Tafel slope (85.9 mV dec-1), and superior OER activity. Especially, the HMT-Co/G-700 catalyst assembled rechargeable zinc-air battery present high-power density (111.0 mW cm-2) and long cycle life at 10 mA cm-2 (576 cycles).