Facile regulation of porous N-doped carbon-based catalysts from covalent organic frameworks nanospheres for highly-efficient oxygen reduction reaction

Abstract

Exploiting inexpensive, highly active and durable electrocatalysts for highly-efficient oxygen reduction reaction (ORR) remains an urgent need. Herein, uniformed covalent organic frameworks (COFs) nanospheres were prepared as the precursors of N-doped porous carbon-based electrocatalyst for ORR reaction. Investigations into the COF-derived N-doped carbon nanospheres (N–CNS) demonstrated that the porous and crystalline frameworks with precise N positions in COF precursors facilitated the regulation of surface area, conductivity, active sites (defects) and their accessibility (pores) in N–CNS via optimizing the pyrolysis temperature. As a result, an excellent ORR catalyst with the activity mostly approximating to that of the commercial 20 wt% Pt/C catalyst among the reported metal-free N-doped carbon-based catalysts to our best knowledge, was obtained, which also exhibited good durability and excellent methanol tolerance. Moreover, Fe3+ was facilely coordinated into COF nanospheres, which therefore derived an ultra-small Fe nanoparticles-decorated N–CNS (Fe–N–CNS) by the simple one-step pyrolysis. This Fe–N–CNS can further enhance its ORR activities (onset potentials, half-wave potentials and limit current density) to be comparable with those of 20 wt% Pt/C catalyst via the synergistic Fe–N active sites. Also, it exhibited good durability and methanol tolerance. All these paved a way to derive COF into the carbon-based electrocatalysts for highly-efficient ORR.