A Facile Synthesis of C‐N Hollow Nanotubes as High Electroactivity Catalysts of Oxygen Reduction Reaction Derived from Dicyandiamide

Development of N‐doped carbon nanotubes (CNTs) with a hollow structure is extremely important for its application to electrochemical catalysis and energy storage. Here we demonstrate a facile synthesis of N‐doped CNTs from direct pyrolysis of a mixture of nickel salt (or nickel / cobalt salts), glucose and dicyandiamide, in which both the N‐doping process and the synthesis of carbon nanotubes are completed. The resulting hybrid N−C composites with high N doping contents show an emblematic tubular morphological structure revealing a hollow interior. Nickel salt is found to be an essential growth catalyst of these N‐doped CNTs and the as‐obtained tubular structure is about 27 nm in diameter in the presence of nickel and cobalt salts. All the as‐prepared catalysts display a comparable onset potential and high current density for ORR compared to Pt/C both in acidic and in alkaline media. Ni−Co/C−N‐HT catalyst even displays an extremely high ORR limiting current density of 7.17 mA cm ‐2@1600 rpm in acidic media, which is more than 1.3 times larger than the Pt/C. ORR in acidic solution takes place via a four‐electron mechanism. And for most of the catalysts a four‐electron mechanism of ORR in alkaline medium also prevails over a two‐electron mechanism.