In Situ-Grown Nitrogen-Doped Carbon-Nanotube-Embedded Two Phases of Bimetal CoFe Alloy and CoFe2O4 Spinel Oxide as Highly Efficient Bifunctional Catalyst for Oxygen Reduction and Evolution Reactions in Rechargeable Zinc–Air Batteries

Abstract

The pedestal of the rechargeable zinc–air battery (ZAB) is based on high-performance bifunctional oxygen reduction/evolution reactions (ORR/OER) electrocatalysts. Herein, without any template or surfactant, in situ grown nitrogen-doped carbon-nanotube (NCNT)-embedded with two phases of bimetal CoFe alloys and CoFe2O4 spinel oxide are constructed, using inexpensive materials of glucose, urea, and cobalt/iron acetates by programing the pyrolysis temperature. The obtained catalyst with optimal cobalt/iron acetates mass ratio (1:1) denoted as CoFe–CoFe2O4–NCNT not only exceeds Pt–Ru/C in terms of ORR half-wave potentials [(0.88 vs 0.84 V versus reversible hydrogen electrode (RHE)] and limiting current densities (6.40 vs 5.40 mA cm−2), but also manifests superior OER activity with the potentials of (1.58 vs 1.67 V versus RHE) at 10 mA cm−2. Therefore, CoFe–CoFe2O4–NCNT exhibits a smaller (Formula presented.) value of (0.70 V versus RHE), surpassing that of Pt–Ru/C (0.85 V versus RHE) and shows excellent stability as well as outstanding methanol tolerance compared with the Pt–Ru/C commercial catalyst. In addition, CoFe–CoFe2O4–NCNT applied as a bifunctional air electrode in rechargeable ZAB displays a promising rechargeability performance with high-discharge and low-charge potentials and a relatively stable potential gap under 550 cycles, outperforming those of Pt–Ru/C.