Efficient nano-size ZnM/rGO (M = Ni, Cu, and Fe) electrocatalysts for oxygen electrode reactions in alkaline media

Abstract

Herein, zinc with nickel, copper, and iron was deposited on reduced graphene oxide (rGO) (ZnM/rGO, M = Cu, Ni, Fe) and examined as novel bifunctional electrocatalysts for oxygen evolution (OER) and oxygen reduction (ORR) reaction in alkaline media. Fourier-transform infrared and X-ray photoelectron spectroscopy, X-ray powder diffraction analysis, transmission, and scanning electron microscopy with energy-dispersive X-ray spectroscopy were used for the examination of structural and morphological properties of ZnM/rGO. ZnFe/rGO showed the lowest OER overpotential and Tafel slope, the highest OER current density with the lowest charge-transfer resistance. Furthermore, ORR at ZnFe/rGO proceeds by mixed 2e/4e mechanism, and by 2e mechanism at the other materials. Still, ZnCu/rGO showed the most positive onset potential and low Tafel slope during ORR. Hence, ZnFe/rGO presents the best OER activity with further improvements needed in terms of its ORR performance to reach full potential for rechargeable metal-air batteries and unitized regenerative fuel cells.