A Comparative Study of Plasma-Treated Oxygen-Doped Single-Walled and Multiwalled Carbon Nanotubes as Electrocatalyst for Efficient Oxygen Reduction Reaction

The oxygen reduction reaction (ORR) is pivotal in renewable energy technologies, such as in fuel cells and metal-air batteries. Precious-metal-free electrochemical ORR is a critical component in designing cost-effective electrochemical energy conversion devices. We show here the surface modification of carbon nanotubes (CNT) through one-step oxygen plasma irradiation, which induces doping and charge redistribution around the doped heteroatom oxygen to promote ORR activity. The generation of defect sites owing to oxygen dopant in CNTs was confirmed by Raman spectra, X-ray photoelectron spectroscopy surface composition, and CHNO elemental analysis. The O-doped CNTs were thoroughly characterized by Fourier transform infrared spectroscopy, scanning electron microscopy, and high-resolution transmission electron microscopy measurements. Our research shows that plasma-treated single-walled carbon nanotubes (SWCNT) are a more effective ORR catalyst compared to multiwalled carbon nanotubes (MWCNT) due to the inherent structure of SWCNT, that can access more defects and surface functional groups than MWCNT. Importantly, for the first time a comparison of doping-induced catalytic activity in ORR is shown here between SWCNT and MWCNT.