Insights into the electrocatalytic behavior of nitrogen and sulfur co-doped carbon nanotubes toward oxygen reduction reaction in alkaline media

Abstract

This study examines the effect of pretreatment and doping to enhance the ORR activity of multiwalled carbon nanotubes (MWCNTs). Melamine and thio-urea are chosen as precursors for mono and co-doping, respectively. A series of samples with pristine and pretreated CNTs are prepared and characterized physicochemically by Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (TEM) and electrochemically by cyclic voltammetry (CV) and linear sweep voltammetry (LSV). The obtained results show that co-doping is an effective way for improving ORR activity, due to the synergistic effect of N and S for changing the charge and spin density, respectively. Moreover, thio-urea favors the proportion of pyridinic and graphitic nitrogen configurations within doped samples. As a consequence, our synthesis method gives samples with superior ORR activity. The maximum ORR activity is obtained for NS-OX-CNTs which shows an over potential of 0.95 V vs RHE at 0.1 mA/cm2, which is comparable to Pt/C (0.98 V vs RHE). The electron transfer number (n) is calculated as 3.9 at 0.4 V which suggests that the ORR proceeds through a dominant 4 e− path. These comparable half-cell results to that of Pt/C pave the way for further testing as cathode materials for anion exchange membrane fuel cells (AEMFC). Graphical abstract

Recent Progress on Carbon‐Based Electrocatalysts for Oxygen Reduction Reaction: Insights on the Type of Synthesis Protocols, Performances and Outlook Mechanisms

“…[89] As reported by Rambabu et al, acid pretreatment can be an efficient step used to remove unwanted impurities on the pristine-MWCNTs and also to induce oxygen-containing functional groups which are essential for doping as shown in Figure 13(e). [87] Defects are introduced on MWCNTs by covalent functionalization and grafting of oxygen functional groups by oxidation and doping as shown by the TEM images in Figure 13(f).…”

“…This shows that the electrochemical response of the prepared NSÀ Ox-MWCNT was close to the commercial Pt/C which is promising. [87] Theophylline (THP) which is used to treat asthma and obstructive chronic pulmonary diseases has abundant nitrogen atoms which provide multiple coordination sites for metal ions, therefore, can act as an ideal candidate to modulate the coordination of metal ions on a carbon framework. [91] With the assistance of THP, Zhang et al, synthesized FeCo/NCNTs-800 by embedding FeCo alloy on nitrogen-doped carbon nanotubes by a one-step pyrolysis method of a mixture of the metal precursors, g-C 3 N 4 and THP as shown in Figure 13(h).…”

“…[88] As shown in Figure 13(i), FeCo/NCNTs-800 outperformed the commercial Pt/C in terms of the onset potential, half wave potential, and current density limit due to the synergistic effect of iron, cobalt, and N-doped carbon. The intern increased the [85] Copyright (2020), with permission from Elsevier, (e) Schematic representation for the oxidation and subsequent heteroatom doping methods to result in NSÀ Ox-CNT, (f) High-resolution TEM images for NÀ Ox-CNTs and NSÀ Ox-CNT, (g) Polarization curves for various catalysts in O 2 saturated 1 M NaOH electrolyte solution at 1600 rpm [87] Copyright © 2023, Springer Nature, (h) Schematic representation for the synthesis of FeCo/NCNTs-800, (i) Polarization curves and chronoamperometric stability test for FeCo/ NCNTs-800 and Pt/C in O 2 saturated 0.1 M KOH solution at 1600 rpm, 10 mV/s, and 0.6 V respectively. Reproduced from [88] Copyright (2022), with permission from Elsevier.…”

Applications of Nanomaterials in Microbial Fuel Cells: A Review

“…Electrons transfer from the anode to the cathode through an external circuit, while the protons transfer through the PEM to the cathode [ 2 ]. There are many factors that affect the performance and efficiency of MFC, such as the organic material used, bacteria (biocatalyst), internal resistance, properties of the electrode material, the membrane, and the concentration of ions [ 3 , 4 , 5 ].…”

“…The electrode materials (anode and cathode) are important in the performance and efficiency of MFC in terms of the type of electrode material, electrical conductivity, biocompatibility, surface area, and non-toxicity to bacteria, which affects the efficiency of the oxidation and reduction processes of organic matter, electron transfer, and electric power generation. In addition, the PEM is an important component in the efficient operation of the MFC in terms of the type of membrane material and the size of the membrane pores, which affects the process of transferring protons and reducing the transfer of oxygen to the cathode [ 5 ]. In MFC systems, anode performance is a critical component that can influence the level of power output that can be reached.…”