Carbon nanotube-bridged N-doped mesoporous carbon nanosphere with atomic and nanoscaled M (M = Fe, Co) species for synergistically enhanced oxygen reduction reaction

Rational design of hierarchically structured carbon nanomaterials and also the facile regulation of their metal species decoration for enhanced oxygen reduction reaction (ORR) are urgently required. Herein, N-doped carbon nanospheres (N-MCN) with plentiful pyridinic and graphitized N-induced active sites were closely bridged with carbon nanotubes to remedy the conductivity loss of N-doping. The as-obtained N-MCN@CNT exhibited hierarchically porous structure with large surfaces area and good conductivity with small charge transfer resistance, which therefore had a superior ORR activity to the other carbon-base catalysts. Importantly, the metal species (M = Fe or Co) can be loaded in this porous N-MCN@CNT via a simple co-pyrolysis, where their numbers and shapes can be easily regulated. It was found the optimal adsorption of metal ions into the precursors produced both single atom and few carbon-coated nanoparticles in M/N-MCN@CNT, which thus synergistically contributed the enhanced ORR performances, including large current density, low onset and half-wave potentials, as well as superior stability and methanol tolerance than those of commercial 20 wt% Pt/C. Moreover, M/N-MCN@CNT also demonstrated comparable oxygen evolution reaction activity to RuO 2 possibly due to the regulated metal species. This work provided a strategy to regulate the nanostructure and intrinsic active sites of carbon-based electrocatalysts.