M. Eikerling (Simon Fraser University)
The formation and reduction of surface oxide species determine both the electrocatalytic activity of Pt towards the oxygen reduction reaction as well as the rate of corrosive Pt dissolution [1]. We perform theory and modeling work to rationalize the various stages of oxide formation and reduction at Pt and, subsequently, use it to explore mechanisms of Pt dissolution. Mechanistic models developed through this work strive to establish relations between metal phase potential and surface oxidation state that govern the transient current response of the electrode. The first part focuses on a recently developed kinetic model for oxide formation and reduction at Pt in the voltage range of 0.65–1.15 V [2]. The model is evaluated against electrochemical [3], spectroscopic [4] and computational studies [5]. The second part presents a kinetic model of oxide growth on platinum in the high voltage regime, above 1.15 V. The governing equations of the oxide growth model account for mass and charge conservation, species migration, and electric field effects. The model is expected to provide insights into different oxide growth mechanisms and to rationalize various growth laws that have been found experimentally. Results will be compared to experimental cyclic voltammetry data to extract rates of kinetic and transport processes. In an ensuing step, platinum dissolution kinetics will be incorporated and linked dynamically to oxide growth and reduction. It is thus expected that the model will be able to explain the dramatically enhanced rate of Pt dissolution that was found in recent experimental studies, when the electrode voltage was cycled through the high voltage regime [6,7,8]. The detailed mechanistic understanding of oxide growth and reduction on platinum will thus complete our theory of platinum dissolution in catalyst layers for polymer electrolyte fuel cells [9].
References
[1] A. Seyeux, V. Maurice, and P. Marcus, J. Electrochem. Soc. 160, C189 (2013).
[2] S. G. Rinaldo, W. Lee, J. Stumper, and M. Eikerling, Electrocatalysis 5, 262 (2014).
[3] A.M. Gómez-Marín, J. Clavilier, J.M. Feliu, J. Electroanal. Chem. 688, 360 (2013)
[4] M. Wakisaka, H. Suzuki, S. Mitsui, H. Uchida, M. Watanabe, Langmuir 25, 1897 (2009)
[5] L. Wang, A. Roudgar, M. Eikerling, J. Phys. Chem. C 113, 17989 (2009)
[6] S. G. Rinaldo, P. Urchaga, J. Hu, W. Lee, J. Stumper, C. Rice, and M. Eikerling, Phys. Chem. Chem. Phys., in press.
[7] A. A. Topalov, S. Cherevko, A. R. Zeradjanin, J. C. Meier, I. Katsounaros, and K. J. J. Mayrhofer, Chemical Science 5, 631 (2014).
[8] L. Xing, M. A. Hossain, M. Tian, D. Beauchemin, K. T. Adjemian, and G. Jerkiewicz, Electrocatalysis 5, 96 (2014).
[9] S. G. Rinaldo, W. Lee, J. Stumper, and M. Eikerling, Physical Review E 86, 041601 (2012).
