Ultrasonic synthesis of nitrogen-doped carbon nanofibers as platinum catalyst support for oxygen reduction

Oxygen- and nitrogen-containing groups are successfully introduced onto the carbon nanofiber (CNF) surfaces by sonochemical treatment in mixed acids (concentrated sulfuric acid and nitric acid) and ammonia, respectively. Pt electrocatalysts supported on the acid-treated CNF (CNF-O) and ammonia-treated CNF (CNF-ON) are prepared and the effect of CNF surface functional groups on the electrocatalytic activities of supported catalysts for oxygen reduction reaction (ORR) is investigated. High resolution transmission electron microscopy reveals that Pt particles are uniformly dispersed on the two CNF supports and the CNF-ON supported Pt nanoparticles have a smaller average particle size and a more uniform particle size distribution. Cyclic voltammetric analysis shows the Pt/CNF-ON has a larger electrochemically active surface area than Pt/CNF-O. Rotating disk electrode measurements show that the Pt/CNF-ON exhibits a considerably higher electrocatalytic activity toward ORR as compared with Pt/CNF-O. It is believed that the good electrocatalytic activity of Pt/CNF-ON can be attributed to the smaller Pt particle size and more uniform particle size distribution, to the synergistic effect and the enhanced Pt–CNF-ON interaction, and to the unique structural and electronic properties of CNF-ON.

► We developed a simple post-doping method to synthesize nitrogen-doped CNFs using a sonochemical process.
► We studied the effect of oxygen- and nitrogen-containing functional groups on the particle size and deposition of Pt nanoparticles.
► Pt/CNF-ON exhibited smaller Pt average particle size and narrower particle size distribution compared with Pt/CNF-O.
► Pt/CNF-ON/GC electrode exhibited a better electrocatalytic activity toward ORR compared with Pt/CNF-O/GC electrode.