FeCoN Co-doped Hollow Carbon Nanocage Grafted with Carbon Nanotubes as an Electrocatalyst for Enhanced Oxygen Reduction Reaction

Significantly maximizing the density of active sites while increasing the mass transfer rate of the catalyst is critical to increasing the activity toward oxygen reduction reaction (ORR). Herein, a Fe, Co, and N co-doped carbon catalyst in the form of hollow carbon nanocage grafted with carbon nanotubes (FeCo-HNC/CNT) was synthesized using a seed-mediated growth method with in situ doping strategy followed by one-step high-temperature pyrolysis without additional acid-etching or re-pyrolysis. Benefiting from the in situ doping of Fe3+ ions, the FeCo-HNC/CNT catalyst exhibited a relatively high content of active sites (M-N), unique concave hollow structure, hierarchical pore structure, and in situ growth of carbon nanotubes. The utilization of active sites and mass transport within the carbon matrix are promoted. Remarkably, the FeCo-HNC/CNT catalyst exhibits significantly high activity with the onset potential (Eonset) of 1.060 V vs RHE and half-wave potential (E1/2) of 0.902 V vs RHE in 0.1 M KOH solution. The stability is also enhanced with only 2.7 mV loss after 10,000 cycles of CV test. The ORR activity of the FeCo-HNC/CNT catalyst (Eonset = 0.926 V vs RHE and E1/2 = 0.817 V vs RHE) is comparable to that of commercial Pt/C catalysts in 0.5 M H2SO4 solution. This work provides a facile and effective method to prepare an efficient bimetal-doped M-N-C carbon-based ORR electrocatalyst with a proper hierarchical porous structure.