Mass production of nitrogen and oxygen codoped carbon nanotubes by a delicately-designed Pechini method for supercapacitors and electrocatalysis

Abstract

Heteroatom-doped carbon nanotubes (CNTs) have great potential in various fields owing to their extraordinary electronic, structural, and mechanical properties. However, large-scale production of heteroatom-doped CNTs in a simple, economical, and highly efficient manner still remains challenging. Here, we report a modified Pechini method (MPM) for high-yield synthesis of N- and O-codoped CNTs (N,O-CNTs), by rapid pyrolysis of a NiCo-polymer precursor forming via a simple sol–gel process. The carbon source (i.e., citric acid) is inexpensive, and the NiCo-polymer material is the single precursor for the preparation of N,O-CNTs via a thermolysis process without the introduction of additional catalysts or carrier gas. Appropriate NiCo-organic coordination and controlled pyrolysis (i.e. heating rate, pyrolysis temperature, and holding time) are demonstrated to play vital roles in this MPM, which are critical for quick generation of small NiCo nanocatalysts with high catalytic activity and simultaneous formation of sufficient space inside the material. The growth mechanism is well studied. Benefitting from the hierarchically porous structure and the synergistic effect of N,O-codoping in the CNTs, the as-synthesized N,O-CNTs manifest excellent electrochemical performance in both supercapacitors and electrocatalysis. Density functional theory simulations show that N and O dopants could increase the densities of states of CNTs near the Fermi level and charge densities of adjacent C atoms, thus leading to improved electrochemical activity. We anticipate that this work will open up a new avenue for a high-yield and economical synthesis of heteroatom-doped CNTs for energy-related applications and beyond.