Engineering Two-Phase Bifunctional Oxygen Electrocatalysts with Tunable and Synergetic Components for Flexible Zn-Air Batteries

HighlightsA novel heterostructured bimetallic Co/CoFe nanomaterial supported on nanoflower-like N-doped graphitic carbon (NC) is prepared through a strategy of coordination construction-cation exchange-pyrolysis.The Co/CoFe@NC exhibits high bifunctional activities with a remarkably small potential gap of 0.70 V between oxygen evolution reaction (OER) and oxygen reduction reaction (ORR), which can be used in liquid and flexible quasi-solid-state rechargeable Zn-air batteries.The density functional theory calculations reveal optimized adsorption energies for intermediates of ORR and OER on heterostructured Co/CoFe@NC. AbstractMetal-air batteries, like Zn-air batteries (ZABs) are usually suffered from low energy conversion efficiency and poor cyclability caused by the sluggish OER and ORR at the air cathode. Herein, a novel bimetallic Co/CoFe nanomaterial supported on nanoflower-like N-doped graphitic carbon (NC) was prepared through a strategy of coordination construction-cation exchange-pyrolysis and used as a highly efficient bifunctional oxygen electrocatalyst. Experimental characterizations and density functional theory calculations reveal the formation of Co/CoFe heterostructure and synergistic effect between metal layer and NC support, leading to improved electric conductivity, accelerated reaction kinetics, and optimized adsorption energy for intermediates of ORR and OER. The Co/CoFe@NC exhibits high bifunctional activities with a remarkably small potential gap of 0.70 V between the half-wave potential (E-1/2) of ORR and the potential at 10 mA cm(2) (E-j=10) of OER. The aqueous ZAB constructed using this air electrode exhibits a slight voltage loss of only 60 mV after 550-cycle test (360 h, 15 days). A sodium polyacrylate (PANa)-based hydrogel electrolyte was synthesized with strong water-retention capability and high ionic conductivity. The quasi-solid-state ZAB by integrating the Co/CoFe@NC air electrode and PANa hydrogel electrolyte demonstrates excellent mechanical stability and cyclability under different bending states.

Automated summary

A novel bimetallic Co/CoFe nanomaterial supported on nanoflower-like N-doped graphitic carbon was prepared as an efficient bifunctional oxygen electrocatalyst. The material exhibited high activities for oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) with optimized adsorption energies. Experimental characterizations and density functional theory calculations revealed the formation of a Co/CoFe heterostructure and synergistic effects between the metal layer and NC support, enhancing electric conductivity and reaction kinetics.