Triggered synergistic effect of Fe single atoms and tiny Co nanoparticles to enhanced oxygen electrocatalysis bifunctionality for zinc-air batteries

Abstract

Developing efficient and stable non-noble metal-based bifunctional electrocatalysts for oxygen reduction and oxygen evolution reactions (ORR and OER) is the key to achieving large-scale commercial application of rechargeable zinc-air batteries (ZABs). Herein, a three-dimensional (3D) porous Fe_SA-Co_NP@NC electrocatalyst featuring well-dispersed Fe-N₄C single-atom and tiny metallic Co nanoparticle sites on N-doped carbon was synthesized through pyrolysis combined with metal macrocyclic compounds coupling methods. The optimized Fe_SA-Co_NP@NC-2 exhibits a desirable bifunctional electrocatalytic activity for ORR (half-wave potential of 0.90 V vs RHE) and OER (potential of 1.53 V vs. RHE at the current density of 10 mA cm⁻²), outperforming the commercial Pt/C + RuO₂ composite catalyst and selected recently reported advanced transition metal-based electrocatalysts. Remarkably, Fe_SA-Co_NP@NC-2-based ZAB displays a high peak power density of 208.38 mW cm⁻², energy density of 847.43 Wh kg_Zn^-1, and promising charge/discharge cycling stability. Experimental and theoretical results collectively corroborate that Fe single atoms and Co nanoparticles are responsible for excellent ORR and OER activity, respectively. Moreover, the adjacent tiny Co nanoparticles effectively optimized the electronic structure of Fe single atoms. They accelerated the desorption of hydroxyl species, thus achieving the synergistically enhanced bifunctional electrocatalytic activity of Fe_SA-Co_NP@NC compared with the isolated Fe single atom and Co nanoparticle electrocatalysts.