Influence of the Synthesis Parameters in Carbon Nanotubes Doped with Nitrogen for Oxygen Electroreduction

Abstract

Nitrogen doped carbon nanotubes (N-CNTs) were synthesized by modified chemical vapor deposition method using a novel two steps thermal technique. Pyridine was used as carbon and nitrogen source and ferrocene as catalyst for nanotubes growth. The effects of reactor temperature and carrier gas flow were investigated using scanning electron microscopy, transmission electron microscopy, Raman spectroscopy, X-ray photoelectron spectroscopy and linear scan voltammetry. Results show that the synthesis temperature and gas flow rate have influence on the physical, chemical and electrochemical properties of the nanostructures. Microscopy studies exhibit that synthesis temperature modify the length, yield and diameter of the N-CNTs. Transmission microscopy electron images show multiwalled carbon nanotubes with the typical bamboo like structures. High temperature and low flow rate generate more defects, as revealed by Raman analyses. N-CNTs synthesized at the highest temperature and flow rate show better electrocatalytic activity toward oxygen reduction reaction with promising lower onset potential and current densities up to 80% when compared to traditional Pt/C. The favorable performance is attributed to the higher nitrogen content and the type of nitrogen species, mainly pyrrolic and pyridinic incorporated in the carbon lattice. For the last decades, platinum (pure and Pt alloys) has been the best and well known electrocatalyst for the oxidation and reduction reactions in fuel cells. However, scarcity, high price and degradation of platinum as catalyst in fuel cell represent a challenge for commercial proposes.1,2 In recent years, there have been efforts to reduce the platinum loading, or even to eliminate it from the electrodes. It is therefore necessary to develop non-Pt catalytic materials available, cheap and electroactive to replace the precious metal. Carbon nanotubes doped with nitrogen (N-CNTs) have reached the point to become an alternative catalyst for oxygen reduction reaction (ORR) in fuel cells cathode. 3 There have been many studies concerning the synthesis of carbon nanotubes doped with nitrogen atoms using different carbon-nitrogen precursors using chemical vapor deposition (CVD) method and having a good electrocatalytic activity for oxygen reduction. Alexeyeva 4 synthesized N-CNTs using acetonitrile as carbon and nitrogen sources. They studied the electrocatalytic reduction of oxygen with and without doped nanotubes in 0.5M H 2 SO 4 solution where the N-CNTs show significantly more activity for ORR than the free-doping nanotubes. Wong 2 obtained N-CNTs through CVD technique using three different chemical precursors as nitrogen sources: aniline (A), diethylamine (DEA) and ethylenediamine. The analysis revealed that the N-CNTs obtained from EDA with 6.5 at. % N was more active for ORR in acidic medium than nanotubes from A and DEA with 5.9 at. % N and 4.3 at. % N, respectively. Other studies 1,[5][6][7][8] have also showed the important role of nitrogen precursors on the N-CNTs structure. Nevertheless, few...

Successful Manufacturing Protocols of N-Rich Carbon Electrodes Ensuring High ORR Activity: A Review

“…The electrochemical properties of the best test sample also stemmed from the surface structure, due to corrugation, and the extensive distribution of defects, which can act as active sites or cause better access to the edge functional groups. Other researchers, Gonzalez et al [145], used melamine as a source of nitrogen and carbon and ferrocene as a catalyst for the growth of N-doped nanotubes to investigate the electrochemical properties in an acidic environment. As expected, the materials produced at 900 • C exhibited higher ORR activity relative to 800 • C synthesis.…”

Investigation of the surface properties of different highly aligned N-MWCNT carpets

“…They defined this peak as gaseous nitrogen, being intercalated between the CNT shells in the vicinity of an internal cavity of the CNT. In contrast, this peak can also be identified as chemisorbed -NOx species, like a nitro group -NO2 or in form of nitrogen oxides of pyridinic nitrogen [33][34][35][36]. For the proof of nitrogen oxides, we measured the N1s and O1s spectra of freshly synthesized N-MWCNT carpets, which were exposed to air for 1 h. We again obtained the peak at around 405.0 eV, but no clear traces of oxygen (~0.1 at.-%, as shown in supplementary data).…”

Synthesis of few-wall carbon nanotubes using methanol/ propanol mixture by chemical vapour deposition

“…Kure et al [18] reported modified commercial microwave ovens with quartz tubes to synthesized CNTs from Polyethylene. Gonzalez et al [19] doping carbon nanotubes with Nitrogen from Pyridine/ ferrocene as sources of carbon and catalyst respectively, by modified chemical vapor deposition method using a novel two steps thermal technique. Many literatures such mentions previously, include modified strategy for preparation of complicating causing to increase the cost of preparing in addition to pre-treatment for sources of carbon before use.…”