Nitrogen/Phosphorus Co-Doped Side-Hole-Rich Carbon Nanotubes As Efficient Metal-Free Catalysts for Oxygen Reduction Reaction

Abstract

Nitrogen/phosphorus co-doped side-hole-rich carbon nanotubes (N,P-HCNT) were fabricated as metal-free electrocatalysts toward oxygen reduction reaction. The multi-walled carbon nanotubes (MWCNT) were simply reacted with hydrogen peroxide, and numerous of holes were formed at the MWCNT surface during the reaction. The resulting side-hole-rich carbon nanotubes (HCNT) were mixed with urea and triphenyl phosphine to incorporate nitrogen and phosphorus into the HCNT. The formation of N,P-HCNT was characterized by some analyses including X-ray photoelectron spectroscopy, field emission scanning electron microscopy and high resolution transmission electron microscopy. The Brunauer-Emmett-Teller analyses were also conducted to confirm the changes in surface properties of the N,P-HCNTs. Rotating ring disk electrode (RRDE) results indicated that the N,P-HCNTs exhibits excellent ORR activity in both acidic and alkaline conditions. In addition, the N,P-HCNT showed good long-term stability and resistance to methanol crossover effect than commercial platinum-based catalysts. Thus, the N,P-HCNT can be a new promising catalysts for oxygen reduction reaction.