Simple combination of a protic salt and an iron halide: precursor for a Fe, N and S co-doped catalyst for the oxygen reduction reaction in alkaline and acidic media

Abstract

The major bottleneck for widespread realization of fuel cells has been the usage of precious-metal-based electrocatalysts, such as Pt/C or Pt-alloy/C, at the cathode. Owing to the high cost and limited natural resources of platinum, nonprecious metal catalysts, such as iron-doped carbons, have emerged as promising substitute catalyst materials. Protic salts and protic ionic liquids can provide a simple, quick, and cost-effective approach for fabricating iron-doped carbons without any additives or high-surface-area carbon supports. We demonstrate here the fabrication of an efficient electrocatalyst based on a protic salt, 1,10-phenanthrolinium dihydrogen sulfate ([Phen][2HSO₄]), in combination with iron(III) chloride, FeCl₃, via nanocasting. A predominantly mesoporous architecture with a narrow pore size distribution was achieved owing to the suitability of the precursors and silica template. The material also exhibited in situ formation of Fe–N bonds in the nitrogen and sulfur co-doped carbons. We found that maximizing the content of this motif was beneficial towards efficient conversion of oxygen into water in alkaline media. The prototype catalyst after post treatment (acid leaching and 2^nd carbonization) also exhibited efficient reduction of oxygen in acidic media. The contribution of Fe–N bonds to the observed activity in acidic solution was less than in alkaline solution. The simplicity of the synthesis of the protic salt and the versatility of the ionic liquid platform make this molecular-level carbon precursor a unique candidate for future development of iron doped catalysts for fuel cells.