A NH4Cl–NaCl mixed salts assisted pyrolysis route for preparation of a high performance Fe/N/C oxygen reduction reaction catalyst

Abstract

The pyrolysis procedure plays a key role in fabricating Fe–N-doped carbon (Fe/N/C) electrocatalysts for the oxygen reduction reaction. In this paper, a new method is presented for preparation of an efficient Fe/N/C oxygen reduction catalyst by employing NH₄Cl–NaCl mixed salts to assist the pyrolysis of a poly-m-phenylenediamine (P-mPDA) precursor. In this approach, the NH₄Cl salt functions as a secondary precursor to increase the nitrogen doping and surface area of the catalyst. The NaCl works as template to construct a continuous 3-dimensional (3D) framework and as a salt sealed reactor for high-temperature pyrolysis. As a result of increased nitrogen doping, and pore engineering, an optimized Fe/N/C ORR catalyst with high surface area, hierarchical pore structure and a high density active sites is obtained. Consequently, the catalytic activities of the resultant Fe/N/C catalyst, represented by the half-wave potentials (E_1/2), are boosted from 0.760 to 0.929 V in 0.1 M KOH basic solution and from 0.66 to 0.79 V in 0.1 M HClO₄ acidic solution, when compared to the Fe/N/C catalyst directly pyrolyzed from the same precursor. The outstanding performance of the catalyst under practical conditions was also assessed with a homemade Zn–air battery.