Synergistic Improvement in Charge Overpotential of Li–O2 Batteries by Oxidized Carbon Nanotubes and Cobalt Nitride Composites

Bifunctional electrocatalysts are important to optimize the overpotential in Li-O-2 battery cycles. Catalysts with a size distribution in the nanometer range perform efficiently because of the availability of numerous active sites. Carbonaceous composites of materials derived from transition metal series are exploited as bifunctional catalysts for oxygen reactions in the Li-O-2 batteries. Cobalt nitride (Co4N) as predicted by density functional theory is believed to possess metallic properties. In this study, we have examined the viability of Co4N nanoparticles to oxygen reactions in Li-O-2 batteries. Oxidized multiwall carbon nanotubes are further added to Co4N nanoparticles to form a composite. Structural characterizations reveal that nanoparticles arranged conformally around the nanotubes, creating active centers for both oxygen evolution and reduction through the nanotube as a charge-transport channel. Electrochemical measurements for Li-O-2 characteristics are performed on both pristine and composite catalysts. The composite catalyst shows a very high specific capacity of 3312 mAh/g after adding the oxidized nanotube. The charge-transfer resistance obtained from the impedance spectra reveal a lower resistance of the composite than the pristine sample, retaining the former's specific capacity until 80 continuous cycles.