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.
Highlights
Concerns regarding the immediate depletion of fossil fuel resources and, more significantly, environmental issues associated with their extensive utilization have pushed interests to seek clean energy conversion systems such as storage units and fuel cells [1,2]
For all of the electrocatalysts, the peak related to the oxygen reduction reaction is not seen for the N2 saturated solution
multiwall carbon nanotubes (MWCNT) doped with the abovesaid elements can be employed as the electrocatalyst of oxygen reduction reaction (ORR)
Summary
Concerns regarding the immediate depletion of fossil fuel resources and, more significantly, environmental issues associated with their extensive utilization have pushed interests to seek clean energy conversion systems such as storage units and fuel cells [1,2].The oxygen reduction reaction (ORR) has secured a unique place in various renewable energy systems mentioned above [3,4,5]. The widespread use of platinum catalyst in the ORR has led to a series of challenges such as exorbitant price, resource insufficiency, and simple poisoning [6,7]. These problems severely limit the commercialization of platinum catalyst for use in renewable energy systems [6,7]. Such intrinsic shortcomings have spurred interest in completely replacing this catalyst with
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