Kinetics of the initial stages of platinum oxidation

Date

2020-08-31

Authors

Stubb, Natalie

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Abstract

The kinetics of the oxidation of platinum metal have long been a topic of interest in the field of electrochemistry. Using a combination of cyclic voltammetry, potential step experiments, and sweep-hold experiments, this research studies the kinetics of the initial stages of oxide growth on Pt(100), Pt(111), and Pt(110) surfaces. By comparing the electrochemical results with surface X-ray diffraction (SXRD) experiments conducted at synchrotron facilities, it was found that the charge of the oxide peak is within 15 μC cm⁻² or about 0.1 ML for all three surfaces. This means that the amount of oxide formed on each surface is similar. It was also determined that the oxide formed on Pt(111) is a Pt(II) species, consistent with an oxide like PtO. From calculations from the potential step experiments, it was determined that on Pt(100) there are two distinct regions of current decay, but that double layer charging is not one of the two seen. Instead, it was determined that the oxidation is likely a two step process with the first step being an adsorption step and the second being a place exchange oxide formation step. It was also found that more charge is passed when conducting potential step experiments to the oxide region from potentials in the hydrogen underpotential deposition (HUPD) region than from potentials in the double layer region. Finally, the results of a sweep-hold experiment on Pt(100) show that the values for charge are similar when calculated via the data from a sweep-hold and potential step experiment from a potential in the double layer region. The results of this research help further the kinetic understanding of the platinum surface during its oxidation and reduction.

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Keywords

platinum, kinetics, oxidation, place exchange, SXRD

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