Nitrogen and Sulfur Co-doped Mesoporous Carbon Materials as Highly Efficient Electrocatalysts for Oxygen Reduction Reaction

Nitrogen and sulfur co-doped mesoporous carbon materials are synthesized by pyrolyzing FeSO4 + poly(ethyleneimine) + template SiO2 mixture at a high temperature without additional dopant precursors. For post-treatment, acid leaching is used to remove the metal, and the heat-treatment is tailored to optimize the catalytic activity of the catalysts toward the oxygen reduction reaction (ORR) in acidic solution. Scanning electron microscopy, X-ray diffraction, low-temperature N2 adsorption, X-ray photoelectron spectroscopy and inductively coupled plasma are used to characterize the catalysts' morphologies, structures, and compositions. Rotating disk electrode and rotating ring-disk electrode techniques are employed to quantitatively obtain the ORR kinetic constants and determine the reaction mechanisms. The ORR activity is highly improved by reheating the catalyst after H2SO4 leaching with improved half-wave potential of 0.68 V vs. RHE, and ORR electron number larger than 3.76. Moreover, increasing the catalyst loading of 800 μg cm−2 exhibits only ∼36 mV deviation from Pt/C. It is believed that the synergetic effect between the Fe-, N- and S-containing active sites and the modified carbon matrix structure due to H2SO4 leaching and reheating should make contribution to the high ORR activity.