Electro-oxidation of ethanol at Pt electrodes with the use of a Dynamic Electrochemical Impedance Spectroscopy (DEIS) technique
Electro-oxidation of ethanol on smooth platinum surfaces was studied in the
temperature range 21C to 140C for 0.2 M ethanol in 0.5 M sulphuric acid.
This was done by use of cyclic voltammetry and electrochemical impedance
spectroscopy. In addition cyclic voltammetry with different ethanol concentrations
from 0.1 M to 1 M, in 0.5 M sulphuric acid was done at room temperature.
Cyclic voltammetry with different ethanol concentrations showed a shift to more
positive potentials for the first oxidation peak in positive going scan as the ethanol
concentration increased. A shift to more positive potentials was also observed for
the oxidation peak in the negative scan as the concentration increased from 0.1
M to 1 M. This indicates that the optimum surface condition is reached at higher
potentials for higher ethanol concentrations. This can be because ethanol and
adsorbed ethanol derivatives take up more active sites at the surface, thus leaving
less active sites available for adsorbed water derivatives which is necessary for the
oxidation of ethanol to acetic acid and CO2.
Cyclic voltammetry was done for increasing temperatures from 21C up to 140C
for 0.2 M ethanol in 0.5 M sulphuric acid. These results showed an increase
in oxidation current for all oxidation peaks as the temperature increased. A
decrease in peak potential for the first oxidation peak was observed for increasing
temperatures. This indicates that the optimum surface condition for ethanol
oxidation is reached at lower potentials at higher temperatures. There was also
seen an decrease in the apparent onset potential of the first oxidation peak as the
temperature increases. These effects can come from increased thermal activity for
water adsorption at higher temperatures. The peak potential for the oxidation
peak in negative going scan increased with increasing temperatures. This can
come from an easier reduction of platinum oxide at higher temperatures.
Dynamic electrochemical impedance spectroscopy measurements was done at
different temperatures from 21C up to 140C for 0.2 M ethanol in 0.5 M
sulphuric acid solution. The results from the measurements at 60C was fitted
to electrochemical equivalent circuits. This gave indications of one kinetically
significant surface adsorbed species in most potential regions with a notable
oxidation current. This in combination with literature suggesting that acetic acid
and acetaldehyde is the major products from ethanol electro-oxidation suggest
that the adsorbed intermediate is something other than CO(ads). Results from
this work together with existing literature on ethanol oxidation was used to give
a suggested simplified reaction mechanism for ethanol electro-oxidation.
Place, publisher, year, edition, pages
Institutt for materialteknologi , 2012. , 83 p.
ntnudaim:7402, MTKJ Industriell kjemi og bioteknologi, Materialkjemi og energiteknologi
IdentifiersURN: urn:nbn:no:ntnu:diva-18864Local ID: ntnudaim:7402OAI: oai:DiVA.org:ntnu-18864DiVA: diva2:566329
Seland, Frode, FørsteamanuensisDahlstrøm, Per KristianSunde, Svein