Carbon dioxide activated carbon nanofibers with hierarchical micro-/mesoporosity towards electrocatalytic oxygen reduction

Abstract

Polyacrylonitrile (PAN)-based carbon nanofibers prepared by electrospinning were physically activated using carbon dioxide as the oxidizing agent. The activation procedure was performed at 800 °C for different periods of time ranging from 15 to 60 min. The activated materials have a hierarchical structure with two sets of pore systems in the micropore range centered at ∼0.8 nm and small mesopore range centered at ∼2.8 nm. The activation not only increased the specific surface area and pore volume to 1123 m² g⁻¹ and 0.64 cm³ g⁻¹, respectively, but also resulted in the evident loss of doped N atoms. The pyridinic and graphitic nitrogen groups are dominant among various N functional groups in the activated samples. CACNF-60, prepared by activating the carbon nanofibers (CNFs) for 60 min, showed excellent electrocatalytic activity for the oxygen reduction reaction (ORR) as well as superior long-term stability and methanol tolerance compared to commercial Pt/C in alkaline media. The excellent electrocatalytic activity of the activated sample is mainly due to its high N content (6.9 at%), unique hierarchical micro-/mesoporosity, and large specific surface area.