Synthesis of mesoporous Fe/N/C oxygen reduction catalysts through NaCl crystallite-confined pyrolysis of polyvinylpyrrolidone

Abstract

Ternary Fe/N/C catalysts are regarded as the most promising candidates for low-cost alternatives to Pt for catalyzing the oxygen reduction reaction (ORR). High-temperature pyrolysis of N-containing carbon precursors in the presence of Fe salts has been a common and efficient route to prepare Fe/N/C catalysts. However, simple pyrolysis usually leads to a large weight loss of N-containing precursors, which not only increases the overall cost of the catalysts, but also results in the catalysts having a low density of active sites. We show herein that this problem can be effectively overcome by dispersing a highly hydrosoluble polymer precursor, namely, polyvinylpyrrolidone (PVP), in NaCl crystallites. The use of the hydrosoluble polymer precursor enables efficient dispersion and confinement of the precursor in NaCl crystallites in a simple solvent evaporation process. The subsequent pyrolysis process not only shows little weight loss, but also produces a mesoporous Fe/N/C ORR catalyst with a remarkably higher specific surface area (414.5 m² g⁻¹) and ORR activity (half-wave potentials, E_1/2 = 0.793 V and 0.878 V vs. RHE, respectively, in acidic and alkaline media) than those of the material prepared without using NaCl confinement (72.9 m² g⁻¹, E_1/2 = 0.634 V and 0.785 V, respectively, in acidic and alkaline media).