Oxygen reduction on chemically heterogeneous iron-containing nanoporous carbon: the effects of specific surface functionalities

Synthetic activated carbon containing iron and sulfur heteroatoms, obtained from polystyrene sulfonic acid-based organic salt, and commercial wood-based carbon containing phosphorous were tested as catalysts for oxygen reduction reactions. The carbons were characterized using adsorption of nitrogen, TA-MS, FTIR, XRD, XPS, potentiometric titration, SEM/EDX, and HR-TEM microscopy. The introduction of iron to the carbon resulted a marked electrocatalytic activity for oxygen reduction reaction (ORR) in alkaline medium. A current density was higher than that on commonly used platinum modified carbon and number of electron transfer (~4e-) indicated a high ORR efficiency. This was accompanied by a high tolerance to methanol oxidation and a good long-term stability after 1500 potential cycles. The extensive surface characterization indicated the fast O2 adsorption and charge transfer was owed to the surface hydrophobicity, small pores and conductivity. The synergistic effect of porosity and specific iron species containing sulfur lead to high ORR activity and high kinetic current densities.