Highly active Fe centered FeM-N-doped carbon (M = Co/Ni/Mn): A general strategy for efficient oxygen conversion in Zn–air battery

In great demand of clean energy conversion devices, ideal electrode materials are expected to have low cost, high efficiency, and long durability in contrast with the benchmarked catalysts (e.g. Pt- and RuO2-based materials) for reversible oxygen electrocatalysis. Herein, a convenient and general strategy is presented for preparation of high-yield FeCo-nitrogen-carbon nanotubes with porous and hollow structure (FeCo-NCNTs), in which the chlorinated metals were initially chelated with 2,4,6-tris(2-pyridyl)-s-triazine (TPTZ), followed by ultimate pyrolysis and acid treatment. The resulting FeCo-NCNTs exhibited outstanding catalytic property for oxygen reduction reaction (ORR, E1/2 = 0.90 V) and oxygen evolution reaction (OER, 320 mV of overpotential at 10 mA cm−2) in alkaline surroundings. Besides, the density functional theory (DFT) calculations revealed that the porous structure created abundant active sites and active Fe-centered FeCo sites greatly reduced the OOH* energy barrier to promote the ORR. Moreover, the FeCo-NCNTs based rechargeable Zn–air battery exhibited high open circuit voltage (1.55 V), large output power density (148 mW cm−2), and robust stability (115 h, 345 cycles), surpassing the mixed Pt/C + RuO2 derived battery. Furthermore, the alternative FeNi-NCNTs and FeMn-NCNFs systems also displayed superior performances in the same environment. This strategy offers a new avenue for rational design of advanced metal-nitrogen-carbon materials with high electrocatalytic performances.