Poisoning of platinum catalyst due to adsorption of carbon monoxide (CO) severely hinders the hydrogen oxidation-evolution reactions due to loss of electrochemically active surface area and changes to the reaction kinetics on the electrodes.^[1,2] This paper presents electrochemical impedance spectroscopy (EIS) data for hydrogen oxidation and evolution in presence of . The system consists of two isolated 10mil diameter platinum electrodes coated with a thin layer of Nafion electrolyte for ionic conduction. Both electrodes are exposed to the same environment. EIS measurements are taken both before and after 6 hours of CO exposure. At the beginning of testing, two distinct semicircles are visible in the Nyquist plots at both low and high potentials ( and ). Following CO poisoning, EIS measurements show a significant increase in the diameters of both semicircles. While the data obtained at high potential () shows an amplification of the original Nyquist plot, the measurements taken at the lower current () have an intermediary curve between the original two semicircles.

In this work, we will look to understand the mechanisms that are at work when CO is present during the hydrogen oxidation/evolution reaction. The impedance spectra will be reproduced using an equivalent electrical circuit (EEC) model to examine what circuit elements replicate the measured EIS data and what can be the cause the introduction of the third curve in the spectrum.

References

1. N.R. Elezovic, Lj. Gajic-Krstajic, V. Radmilovic, Lj. Vracar and N.V. Krstajic, Electrochim. Acta, 54, 1375 (2009).
2. G.A. Camara, E.A. Ticianelli, S. Mukerjee, S.J. Lee and J. McBreen, 149(6), A748 (2002).