Doped, Defect‐Enriched Carbon Nanotubes as an Efficient Oxygen Reduction Catalyst for Anion Exchange Membrane Fuel Cells

Abstract

Bond polarization of doped atoms and carbon and lattice defects are considered important aspects in the catalytic mechanisms of oxygen reduction reaction (ORR) on heteroatom‐doped carbon catalysts. Previous work on metal‐free catalysts has focused either on bond polarization or lattice defects. Here multi‐heteroatom doped defect‐enriched carbon nanotubes (MH‐DCNTs) that combine both effects to enhance ORR activity are designed. Lattice defects in MH‐DCNTs are enriched by unzipping and length‐shortening of carbon nanotubes, and also by creating carbon vacancies via decomposition of doped F atoms. Electrochemical analysis using rotating disc electrode voltammetry shows that the ORR kinetic current density of MH‐DCNT increases with lattice‐defect density, the latter of which is verified by Raman spectroscopy, while the onset potential increases with annealing temperatures. An optimized MH‐DCNT ORR catalyst exhibits a half‐wave potential of 0.81 V versus reversible hydrogen electrode and limiting current density of 5.0 mA cm−2 at an electrode rotation speed of 1600 rpm in 0.1 m KOH. Further, it is demonstrated that MH‐DCNT, as a cathode catalyst layer in an anion exchange membrane fuel cell (AEMFC), delivers a peak power density of 250 mW cm−2, which is ≈70% the performance of an AEMFC using a conventional Pt/C catalyst.

Defect and Doping Co-Engineered Non-Metal Nanocarbon ORR Electrocatalyst

“…Interestingly, it also shows a high ORR activity under universal pH conditions including alkaline, neutral, and acid media. Inspired by this, Pham et al [ 148 ] also synthesized multi-heteroatom-doped defect-enriched CNTs (MH-DCNTs) catalyst by using aggressive oxidation of CNTs and followed high-temperature heteroatom doping. By unzipping and length shortening of CNTs, many lattice defects with carbon vacancies are in the presence of MH-DCNTs.…”

Wall‐ and Hybridisation‐Selective Synthesis of Nitrogen‐Doped Double‐Walled Carbon Nanotubes

“…The voltammetric curves in an argon saturated aqueous 0.1 M KOH solution show no redox processes, but in an oxygen saturated solution, the voltammograms reveal a reduction wave characteristic of the oxygen reduction reaction, [2-4, 6-7, 9, 11, 13-14] in which the presence and bonding of nitrogen atoms are directly linked to the electrode potentials. [19][20][21][22][23][24][25] The glassy carbon (GC) electrodes containing N-SWNT@SWNT show more anodic potentials at 1 mAcm 2 than those containing pristine SWNT (0.564 V vs NHE). Furthermore, the potential at 1 mAcm 2 of the N-SWNT@SWNT (1300 ºC) with 83.8% of graphitic nitrogen (0.580 V vs NHE) is more anodic than that of N-SWNT@SWNT (1400 ºC) with 100.0% of graphitic nitrogen (0.685 V vs NHE).…”

Wall‐ and Hybridisation‐Selective Synthesis of Nitrogen‐Doped Double‐Walled Carbon Nanotubes

“…The electrochemical properties of N‐SWNT@SWNT were investigated by cyclic voltammetry in a rotating disk electrode (Figures a and S5; Table S2). The voltammetric curves in an argon saturated aqueous 0.1 m KOH solution show no redox processes, but in an oxygen saturated solution, the voltammograms reveal a reduction wave characteristic of the oxygen reduction reaction, in which the presence and bonding of nitrogen atoms are directly linked to the electrode potentials . The glassy carbon (GC) electrodes containing N‐SWNT@SWNT show more anodic potentials at 1 mA cm −2 than those containing pristine SWNT (0.564 V vs. NHE).…”