4 research outputs found
Supplementary document for Non-reciprocal electromagnetic metasurface based on the nonlinearity of a liquid metamaterial - 6585161.pdf
Optimization descriptio
Electrochemical Reduction of Oxygen on Hydrophobic Ultramicroporous PolyHIPE Carbon
A new kind of polyHIPE (polymerized
high internal phase emulsion)-based
carbon derived from coreacted furfuryl alcohol and tannin was tested
as an ORR catalyst. To understand the reduction process, the surface
was extensively characterized from the point of view of texture and
chemistry. The prepared materials show subtle differences in the chemistry
but marked differences in the porosity. The best-performing sample
had a very high volume of ultramicropores and the highest degree of
defects on the surface. The oxygen was present on the surface mainly
in epoxy and ether configurations. Those oxygen groups located in
large pores promoted transfer of O<sub>2</sub> dissolved in water/electrolyte
to small pores of the hydrophobic surface. There, a strong adsorption
of oxygen was energetically favorable. This led to weakening of OâO
bonds, subsequent dissociation of oxygen, and its reduction/protonation.
The presented polyHIPE carbons show high electrochemical stability
and better tolerance to methanol than Pt/C. High kinetic current density
was measured on them
Conversion of Natural Tannin to Hydrothermal and Graphene-Like Carbons Studied by Wide-Angle Xâray Scattering
The atomic structure of carbon materials
prepared from natural
tannin by two different techniques, high-temperature pyrolysis and
low-temperature hydrothermal carbonization, was studied by wide-angle
X-ray scattering. The obtained diffraction data were converted to
the real space representation in the form of pair distribution functions.
The X-ray photoelectron spectroscopy measurements provided information
about the chemical state of carbon in tannin-based materials that
was used to construct final structural models of the investigated
samples. The results of the experimental data in both reciprocal and
real spaces were compared with computer simulations based on the PM7
semiempirical quantum chemical method. Using the collected detailed
information, structural models of the tannin-based carbons were proposed.
The characteristics of the investigated materials at the atomic level
were discussed in relation to their preparation method. The rearrangement
of the tannin molecular structure and its transformation to graphene-like
structure was described. The structure of tannin-based carbons pyrolyzed
at 900 °C exhibited coherently scattering domains about 20 Ă
in size, consisting of two defected atomic layers and resembling a
graphene-like arrangement
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 foamâgraphene 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