Multifunctional carbon armor: Synchronously improving oxygen reaction kinetics, mass transfer dynamics, and robustness of transition metal alloy based hybrid catalyst

Abstract

Construction of robust protective cover on delicate active sites is a frequently-used scheme to enhance the durability of air-cathode catalyst working in harsh environment, thus the lifespan of rechargeable Zinc-air batteries (ZABs). Paradoxically, this would degrade the activity due to the constricted accessibility of active sites to reactants. Herein, carbon nanotubes with abundant mesoporous defects and Fe-N4 species were elaborately designed to be multifunctional protective armor to encapsulate Ni3Fe nano-alloys (Ni3Fe@CNTs/Fe-N4) for bifunctional oxygen electrocatalyst. In/ex-situ spectroscopy analysis and theoretical calculations reveal that the constructed mesoporous carbon defects effectively facilitate the multiphase mass transfer and the oxygen evolution reaction kinetics via strong electrons coupling with packaged Ni3Fe nano-alloys. Meanwhile, the synchronously introduced Fe-N4 moieties could serve as oxygen reduction active sites. Thus, the obtained Ni3Fe@CNTs/Fe-N4 hybrid electrocatalyst simultaneously exhibits remarkable bifunctional catalytic activity (E1/2=0.86/Ej=10=1.59 V vs RHE) and durability over 450 h in the chronoamperometric test at 1.59 V, endowing the assembled Zn-air batteries (ZABs) with a high power density (150 mW cm−2) and lifespan (307 h), much better than that employing benchmark Pt/C+RuO2 mixed catalyst. This work demonstrates an innovative design route for the multifunctional armor to concurrently enhance the durability, activity and robustness of air-cathode-catalyst for ZABs.