Combined Effect of Porosity and Surface Chemistry on the Electrochemical Reduction of Oxygen on Cellular Vitreous Carbon Foam Catalyst

A new mechanism of O2 reduction, which follows principles different from those generally accepted for describing ORR reduction on heteroatom-doped carbons, is suggested. It is based on the ability of oxygen to strongly adsorb in narrow hydrophobic pores. In this respect, a cellular vitreous carbon foam–graphene oxide composite was synthesized. The materials were doped with sulfur and nitrogen and/or heat-treated at 950 °C in order to modify their surface chemistry. The resultant samples presented a macro-/microporous nature and were tested as ORR catalysts. To understand the reduction process, their surfaces were extensively characterized from texture and chemistry points of view. The treatment applied markedly changed the volumes of small micropores and the surface hydrophilicity/polarity character. The results showed that the electron transfer number was between 3.87 and 3.96 and the onset potential reached 0.879 V for the best-performing sample. It is noteworthy that the best-performing sample has the ...