Proposal of a Facile Method to Fabricate a Multi-Dope Multiwall Carbon Nanotube as a Metal-Free Electrocatalyst for the Oxygen Reduction Reaction

Abstract

In this study, a one-pot, low-temperature synthesis method is considered for the fabrication of heteroatom dope multiwall carbon nanotubes (MWCNT). Doped MWCNT is utilized as an effective electrocatalyst for oxygen reduction reaction (ORR). Single, double, and triple doping of boron, nitrogen and sulfur elements are utilized as the dopants. A reflux system with temperature of 180 °C is implemented in the doping procedure. Actually, unlike the previous studies in which doping on the carbon structures was performed using a furnace at temperatures above 700 °C, in this green and sustainable method, the triple doping on MWCNT is conducted at atmospheric pressure and low temperature. The morphology and structure of the fabricated catalysts were evaluated by Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and Raman spectroscopy. According to the results, the nanoparticles were encapsulated in the carbon nanotubes. Aggregated clusters of the sulfur in the case of S-MWCNT are considerable. Cyclic voltammetry (CV), rotating disk electrode, linear sweep voltammetry (LSV), and chronoamperometry electrochemical tests are employed for assessing the oxygen reduction activity of the catalysts. The results illustrate that by using this doping method, the onset potential shifts to positive values towards the oxidized MWCNT. It can be deduced that by doping the N, B, and S atoms on MWCNTs, the defects in the CNT structure, which serve as active sites for ORR application, increase. The N/S/B-doped graphitic layers have a more rapid electron transfer rate at the electrode/electrolyte interface. Thus, this can improve the electrochemistry performance and electron transfer of the MWCNTs. The best performance and electrochemical activity belonged to the NB-MWCNT catalyst (−0.122 V vs. Ag/AgCl). Also, based on the results gained from the Koutecky–Levich (KL) plot, it can be said that the ORR takes place through the 4 e− pathway.

Progress of Nonmetallic Electrocatalysts for Oxygen Reduction Reactions

“…Carbon nanotubes are one-dimensional materials with a special structure (nanoscale radial dimensions, micrometer-scale axial dimensions and sealed ends at both ends of the tube). They are well known for their excellent mechanical strength, stability and conductivity and large specific surface areas, making them highly favored in the field of electrochemistry as electrode materials [ 28 ]. The tube ends and defects of carbon nanotubes have a certain catalytic activity and can directly catalyze oxygen reduction.…”

A Review of One‐Dimensional Nanomaterials as Electrode Materials for Oxygen Reduction Reaction Electrocatalysis

“…All of these merits will bring more advantages for electrocatalysis. Recently, Bakhtavar et al [71] . developed a one‐pot low‐temperature synthesis method to prepare heteroatom‐doped MWCNTs (Figure 5e).…”

Revolutionizing Fuel Cell Efficiency with Non-Metallic Catalysts for Oxygen Reduction Reactions

“…It can be seen that both electron-deficient B-doping and electron-rich N-doping can activate π-electrons in sp 2hybridized carbon to give it good catalytic properties [19]. In addition to the two elements N and B, S and P doped carbon materials can exhibit good electrocatalytic properties.…”