Abstract
Iron and nitrogen doping of carbon materials is one of the promising pathways towards replacing Pt/C in polymer electrolyte fuel cell cathodes. Here, we show a synthesis method to produce highly active non-precious metal catalysts and study the effect of synthesis parameters on the oxygen reduction reaction (ORR) activity in high-pH conditions. The electrocatalysts are prepared by functionalizing silicon carbide-derived carbon (SiCDC) with 1,10-phenanthroline, iron(II)acetate and, optionally polyvinylpyrrolidone, by ball-milling with ZrO2 in dry or wet conditions, followed by pyrolysis at 800 °C. The catalysts are characterized by scanning and transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray absorption spectroscopy, N2 physisorption and inductively coupled plasma mass spectrometry. By optimizing the ball-milling conditions, we achieved a reduction in the size of SiCDC grains from >1 μm to 200 nm without negatively affecting the high BET area of catalysts derived from SiCDC. This resulted in increased ORR activity in both rotating disk electrode and anion exchange membrane fuel cell (AEMFC) environments, and improved mass-transport properties of the cathode layer in fuel cell. The ORR activity at 0.9 V in AEMFC of the optimized iron and nitrogen-doped SiCDC reaches 52 mA cm−2, exceeding that of a Pt/C cathode at 36.5 mA cm−2.