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

• We synthesized MOx/CNT nano-composite catalysts by depositing metal oxides onto functionalized CNTs.
• We evaluated the electrochemical activity of the catalysts in alkaline media using Rotating Disc Electrode experiments.
• The catalysts were characterized by XRD, SEM, TEM, XPS and BET techniques.
• The catalysts are bifunctionally active and have the potential to replace PGM-based catalysts.
• Usage of such catalysts can assist in decreasing the dependence on petroleum-derived fuels.

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 FexOy) 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 50 wt% MnO2/CNT catalyst with a half-wave potential of 0.84 V at the current density of −2.1 mA cm−2 and an onset at 0.98 V versus RHE. The most active for OER is the 50 wt% NiO/CNT catalyst with an onset potential at 1.45 V versus RHE.

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