Cobalt Nanoparticles Confined in Carbon Cages Derived from Zeolitic Imidazolate Frameworks as Efficient Oxygen Electrocatalysts for Zinc-Air Batteries

Abstract

Rechargeable zinc (Zn)-air batteries are a potential solution to effectively incorporate electricity generated from renewable energy sources into our daily consumption, which requires electrocatalysts to catalyze the oxygen-reduction reaction (ORR) and the oxygen evolution reaction (OER) on the air electrode. Here, we report a high-performance bifunctional oxygen electrocatalyst by confining cobalt (Co) nanoparticles in nitrogen (N)-doped porous carbon cages derived from a metal-organic framework, i. e., ZIF-8. Co precursors were first impregnated into ZIF-8 by a double solvent method. Afterward, carbonization produces highly dispersed Co nanoparticles (with the average diameter of 6.2 nm) confined in N (11.4 at.%) doped porous carbon cages (434.5 m2 g−1). This electrocatalyst exhibits excellent catalytic activity for both ORR and OER with long-term stability. It delivers a half-wave potential of 0.838 V vs. reversible hydrogen electrode, an electron transfer number of 3.9 for ORR, an overpotential of 0.411 V at 10 mA cm−2, and a Tafel slope of 71.2 mV dec−1 for OER. Rechargeable Zn-air batteries assembled using this electrocatalyst demonstrate an open-circuit potential of 1.48 V, a specific capacity of 731.1 mAh g−1, and good rechargeability. The simple and efficient method can confine metal nanoparticles in porous carbon cages, which can be further explored to synthesize novel electrocatalysts for various energy conversion applications.