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 Delta E 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.