Nitrogen Doping Effects on Carbon Nanotubes and the Origin of the Enhanced Electrocatalytic Activity of Supported Pt for Proton-Exchange Membrane Fuel Cells

Abstract

Carbon nanotubes (CNTs) and nitrogen-doped carbon nanotubes (CNx) were synthesized by the floating catalyst chemical vapor deposition (FCCVD) method. Pt nanoparticles were deposited onto the two catalyst supports with the ethylene glycol reduction method. Different from CNTs that contain straight hollow tubes, CNx contain a bamboolike structure with kinks along the tubes and more surface defects. X-ray photoelectron spectroscopy (XPS) confirms the nitrogen atoms in the graphite matrix and reveals the chemical natures of the doped nitrogen atoms. Carbon K-edge near-edge X-ray absorption fine structure (NEXAFS) and Raman characterizations reveal higher defectiveness in CNx than CNTs. The unique structure and surface property of CNx leads to a better dispersion of Pt nanoparticles on CNx than on CNTs, as revealed by TEM images. Pt supported on CNx (Pt/CNx) exhibited a higher electrochemical surface area (ECSA) and higher catalytic activity toward oxygen reduction reaction (ORR), in comparison to Pt supported on CNTs (Pt/CNTs). Better performance of Pt/CNx than Pt/CNTs has been confirmed by single-cell fuel cell tests.

Understanding Heteroatom-Mediated Metal–Support Interactions in Functionalized Carbons: A Perspective Review

“…A shift toward higher values was produced also in N 1s BE in species interacting with Pt. In addition, the appearance of new components in the N 1s spectra was assigned alternatively to chemisorbed nitrogen oxide (405.2 eV) [84] deriving from the conversion of graphitic nitrogen, or to a nitride (398.1 eV) resulting from the presence of a metal-nitrogen bond. Similar results were obtained in the case of Pt-N and Au-N [81] interactions.…”

CNx-modified Fe3O4 as Pt nanoparticle support for the oxygen reduction reaction

“…Figure 3 also shows that the peaks of Fe 3 O 4 -PPy disappeared after the carbonization step. Here, the positions and intensities of the peaks can provide information about the structure changes occurring on the surface of the catalysts, namely graphite layer defectiveness, resulting from nitrogen doping [26]. In the curves of G-band).…”

Pt and Pt/Ni "Needle" Eletrocatalysts on Carbon Nanotubes with High Activity for the ORR

“…This ultimately eliminates the performance advantage and results in similar electrochemical stability problems that are seen with carbon black supports [13]. Nitrogen doping is another method for increasing Pt coverage on CNTs while avoiding the detrimental functionalization process using strong acids [14]. Nitrogen doping has been shown to increase the durability of Pt catalyst by providing structural defects as anchoring sites and therefore preventing metal nanoparticle agglomeration [3,15,16].…”