(Fe,Co)/N-Doped Multi-Walled Carbon Nanotubes as Efficient Bifunctional Electrocatalysts for Rechargeable Zinc-Air Batteries

Graphical Peak Power ! Novel hybrid materials composed of N-doped carbon nanotubes (CNTs) with several embedded Fe−Co alloy nanoparticles (CNTs@(Fe,Co)PP) that can serve as highly efficient bifunctional oxygen electrocatalysts are derived from bimetallic Fe/Co-coordinated polyporphyrin-CNTs self-assemblies via pyrolysis. The optimal electrocatalyst is used at air electrode in zinc-air battery (ZAB) delivering a higher peak power density and showing a better long-term cycling stability than a ZAB containing the noble metal electrocatalysts Pt/C+RuO 2 . The design and fabrication of efficient, less costly, and stable bifunctional oxygen electrode electrocatalysts is crucial for large-scale production of rechargeable zinc-air batteries. Herein, electrocatalytically active, hybrid materials composed of Fe−Co alloy nanoparticles-embedded N-doped carbon nanotubes (CNTs) are synthesized from Fe/Co-polyporphyrin-CNTs via pyrolysis. The materials serve as highly effective bifunctional oxygen electrode catalysts for zinc-air batteries. In particular, the one synthesized at 700 °C, named CNTs@(Fe,Co)PP-700, shows a very good activity for both the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) in an alkaline solution. This material catalyzes ORR with a limiting current density of 5.11 mA cm −2 and a half-wave potential of 0.86 V vs RHE. It also catalyzes OER with 10 mA cm −2 at a small overpotential of 360 mV. Besides, it operates well as an air cathode in a home-made rechargeable zinc-air battery, with a small voltage gap of 0.71 V at 2 mA cm −2 , while remaining stable in hundreds of charge-discharge cycles for >83 h. Its performance in a zinc-air battery is better than that of a benchmark air-electrode containing noble metals, Pt/C+RuO 2 .