Atomic iron coordinated by nitrogen doped carbon nanoparticles synthesized via a synchronous complexation-polymerization strategy as efficient oxygen reduction reaction electrocatalysts for zinc-air battery and fuel cell application

Developing atomic transition metal coordinated by nitrogen doped carbon (M−N−C) eletrocatalysts for oxygen reduction reaction (ORR) is critical to achieve low cost metal-air batteries and fuel cells. Herein, a general method of synthesizing M−N−C was developed via a synchronous complexation-polymerization strategy, in which nitrogen-containing ligand was coordinated with specific transition metal ions and diamino aromatic compound was simultaneously polymerized by the metal ion as initiator; by the following pyrolysis in a molten NaCl bath, M−N−C was finally synthesized. Fe-N-C was synthesized by this strategy using 2, 4, 6-Tri (2-pyridyl)-1, 3, 5-triazine (TPTZ) as ligand for FeCl2, and 1, 8-Diaminonaphthalene (DAN) as monomer of polymerization. Results demonstrate that introducing DAN into TPTZ-Fe2+ significantly affect the derived carbon structure and electrochemical performance of corresponding Fe-N-C. The Fe-N-C prepared by TPTZ and DAN with the molar ratio of 1:1 shows excellent ORR activity and durability, whose initial half-wave potential is 0.90 V in 0.1 M KOH and 0.80 V in 0.5 M H2SO4 respectively, after 10 K cycles, the potential is only 14 mV loss in 0.1 M KOH and 20 mV decay in 0.5 M H2SO4. And the ORR performance as cathode is further proved by a single practical Zn-air battery with a maximum power density of 192 mW cm−2 and a specific capacity of 800 mAh gZn-1, much higher than 137 mW cm−2 and 735 mAh gZn-1 of the same loading of commercial Pt/C catalyst and proton exchange membrane fuel cell with a high power output of 640 mW cm−2. Attributed to the vast kinds of ligands, metal ions and polymerizing monomers, this strategy provides a flexible platform of synthesizing advanced M−N−C catalysts, compared with other reported methods.