Metal oxides/CNT nano-composite catalysts for oxygen reduction/oxygen evolution in alkaline media

A series of highly active state-of-the-art catalysts have been synthesized by depositing high loadings of transition metal oxides (MnO₂, Co₃O₄, NiO, CuO and Fe_xO_y) onto nitrogen-doped carbon nanotubes (CNTs) for bi-functional catalysis in alkaline media. The metal oxides have been dispersed onto functionalized CNTs by an improved impregnation method. This novel, synthetic approach allows for both the preparation of functionalized nitrogen-doped CNTs as well as the even dispersion of metal oxides onto the walls of the CNTs. The catalysts have been characterized by Brunauer-Emmett-Teller (BET), scanning electron microscopy (SEM), transition electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) methods. Catalytic activity has been measured using a Rotating Disc Electrode (RDE) experiment. The resulting catalysts are stable in alkaline media under experimental conditions and have high bi-functional electrocatalytic activity-both for the oxygen reduction reactions (ORR) and oxygen evolution reactions (OER). From this series of catalysts, the most active catalyst for ORR is the 50wt% MnO₂/CNT catalyst with a half-wave potential of 0.84V at the current density of -2.1mAcm^-2 and an onset at 0.98V versus RHE. The most active for OER is the 50wt% NiO/CNT catalyst with an onset potential at 1.45V versus RHE.