A CoOx/FeOx heterojunction on carbon nanotubes prepared by plasma-enhanced atomic layer deposition for the highly efficient electrocatalysis of oxygen evolution reactions

Abstract

In this study, FeO_x and CoO_x thin films were successively and uniformly coated on high-surface-area carbon nanotubes by plasma-enhanced atomic layer deposition, which formed a heterojunction of the two oxides. As an electrocatalyst in the oxygen evolution reaction (OER), CoO_x/FeO_x/CNTs showed excellent electrocatalytic performance in terms of catalytic activity and stability. The overpotential of CoO_x/FeO_x/CNTs in OER was only 308 mV at 10 mA cm⁻², which was lower than those of the pure oxides: CoO_x/CNTs (392 mV) and FeO_x/CNTs (406 mV). The as-prepared electrocatalyst also displayed better stability than the reference RuO₂ material, with almost no attenuation of current density in contrast to the 10% loss seen with RuO₂. The OER performance of CoO_x/FeO_x/CNTs was superior to those of its oxide components due to the formation of heterojunction, which led to a smoother reaction path and a lower overpotential for OER compared to pure oxides, as supported by the density-functional theory (DFT) calculations. These results provide a new direction for the preparation of electrocatalysts for metal–air batteries and water splitting reactions.