1 research outputs found
Combined Effect of Porosity and Surface Chemistry on the Electrochemical Reduction of Oxygen on Cellular Vitreous Carbon Foam Catalyst
A new
mechanism of O<sub>2</sub> 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 highest
volume of pores smaller than 0.7 nm while there was no heteroatom
doping. The hydrophobicity and the strong adsorption forces provided
by these pores to pull oxygen inside are the possible reasons for
the observed excellent performance. A decrease in the volume of these
pores resulted in a decrease in the catalytic performance. When the
surface was modified with heteroatoms, the performances worsened further
because of the induced hydrophilicity