Keywords

Catalysis, Electrochemistry, Electrodes, Electrolytic reduction, Fuel cells, Gold, Platinum, Voltammetry, Oxygen reduction reaction

Abstract

Platinum-gold and nanoceria-modified platinum-gold electrodes were prepared on a platinum surface via electrochemical reduction of solutions of platinum and gold salts in the dispersion of nanoceria. The molar ratios of Pt and Au were varied in both PtAu and PtAu/CeO₂ electrodes while the total concentration of the metals was maintained at 2 x 10⁻³M and the concentration of nanoceria was maintained constant at 5 x 10⁻³M. The electrodes were characterized by their cyclic voltammetry curves in 0.5M sulfuric acid solution. The electrochemically active area of the electrodes was determined using the copper underpotential deposition method. The linear sweep voltammograms of the PtAu and PtAu/CeO₂ electrodes were plotted from -1V to 0V vs. Ag/AgCl, 3M KCl reference electrode using the rotating disk electrodes for the rotation speeds from 200 to 3600rpm in an oxygen saturated 0.1M sodium hydroxide solution. The values of the kinetic controlled current density were determined from the rotating disk voltammetry. The values of the limiting current density for each rotation speed were used to plot the Koutecky-Levich plots for the electrodes. The rate constants were obtained from the Koutecky-Levich plots for each composition of the electrode. The values of kinetic current density and the rate constants indicated that the addition of Au enhances the ORR rates in both the PtAu and the PtAu/CeO₂ electrodes. The values of the kinetic current densities of the PtAu/CeO₂ were lower than that of the PtAu electrodes owing to the poor electrical conductivity of ceria. The Koutecky-Levich plots for the PtAu and the PtAu/CeO₂ electrodes are linear for the four-electron reduction of oxygen in the alkaline media, which indicates that the overall reaction follows the first order kinetics. The electron transfer rate constants obtained from the Koutecky-Levich plots for the PtAu and the PtAu/CeO₂ electrodes both were found to increase in values with the addition of Au. The Tafel plots were plotted for the PtAu and PtAu/CeO₂ electrodes and the values of Tafel slopes were found to be in a small range for lower amounts of Au which indicated that the ORR rates were enhanced in lower amounts of Au. The values of Tafel slopes were found to be much higher for the ceria-modified PtAu electrodes as compared to the PtAu electrodes, which indicate the lower rates of ORR after the modification with ceria. Also, the ORR rates for the electrodes with smaller amounts of Au in PtAu/CeO₂ were higher than those in the larger amounts of Au.

Notes

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Graduation Date

2011

Semester

Spring

Advisor

Diaz, Diego J.

Degree

Master of Science (M.S.)

College

College of Sciences

Department

Chemistry

Format

application/pdf

Identifier

CFE0003639

URL

http://purl.fcla.edu/fcla/etd/CFE0003639

Language

English

Release Date

May 2011

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

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