Nitrogen inclusion in carbon nanotubes initiated by boron doping and chlorination: Their use as electrocatalysts for oxygen reduction reaction

Abstract

The use of carbon nanostructures doped with heteroatoms as electrocatalysts for oxygen reduction reaction (ORR) has attracted intense research in recent years because they are highly conductive, have good durability, and are highly electro-active. One of the strategies to modify the characteristics of carbon nanomaterials (CNMs) to render them suitable for certain applications is to dope them with boron (B) and nitrogen (N). The effect of doping CNMs with boron has been a subject of little study, and hence, it is not well understood, as compared to nitrogen doping studies. In this study, nitrogen was unintentionally doped into carbon nanotubes (CNTs) by chlorination and decomposition of triphenylborane in a catalytic vapor deposition (CVD) reactor. N-doping resulted from the use of nitrogen as a carrier gas. Microscopic and spectroscopic techniques revealed that N bonding of carbon nanostructures together with the presence of defects played pivotal roles in determining the extent of ORR performance of produced CNMs. The introduction of N in the carbon matrix during B molecule decomposition resulted in the reduction in the amount of B doped into the matrix, due to competitive incorporation of N which inhibited B introduction. The presence of pyridinic N species was responsible for a 2e− ORR performance.

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“…The surface wettability towards the electrolyte, afforded by the presence of surface functional groups, was claimed to be crucial for the supercapacitive performance of the materials developed in that study. Maboya et al (2022) prepared N-doped carbon nanotubes using their boron-doped carbon counterparts as the starting materials. It was observed that the introduction of nitrogen functional groups during the decomposition of the Bcontaining molecule led to a reduction in B content, which was attributed to the competitive incorporation of both heteroatoms.…”

“…Doping CNTs with B or N is also important for different applications. In this case, Maboya et al (2022) designed the synthesis of CNT doped with N and B via a chlorination method using triphenylborane as the B source, whereas the N 2 used for the bubbling provides the nitrogen source. The catalyst for the CNT was FeCo/CaCO 3 catalyst, which was later removed by refluxing the material in 3M KOH.…”

“…Thus, it is important to develop materials for ORR. In this sense, Maboya et al (2022) reported the synthesis of CNTs doped with N and B which proceeded the ORR via a 2-electron pathway ascribed to the presence of pyridinic N species. Meanwhile, Gouda et al (2020) synthesized rGO and rGO with magnetic iron oxide materials for preparing the anode and the cathode of a membrane electrode assembly (MEA).…”