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

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 approximate to 70% the performance of an AEMFC using a conventional Pt/C catalyst.